Simoco SRM9000-Based Radio Rebroadcast & Repeater Devices.

MRMap -
MRMap-GPS-Tracking-Communications-Safety-Mountain Rescue-Mapping-Downloads-Free Software
Rebroadcast Manual
Simoco SRM9000-Based Radio Rebroadcast
& Repeater Devices.
Collated By The LDSAMRA Communications Sub Committee
On behalf of the contributing teams of the North West of
England and Southern Scotland.
Rev C 14 January 2009
MRMap Development Team 14/01/2009
As a result of a meeting held at Keswick MRT HQ on 6th September 2005, this document has
been produced in order that information presented at the meeting but considered too detailed
for inclusion in the minutes, might be passed on to all interested parties. It is not pitched at
any presumed level of understanding and some things are explained even though
they may be obvious to all. Conversely, anything that’s not obvious can be explained in greater detail, by one or more of the contributors.
The sections included have come from the team responsible for developing the device or concept and the author is responsible only for graphics and writing up or collation of the various
All re-broadcast devices are based upon current Simoco radio equipment and thanks are due
to Team Simoco Ltd in Derby and Huntingdon, and TMC Radio Pty Ltd in Australia for their
help in resolving issues that arose during the construction of these devices.
In the majority of cases, the wiring associated with power supply, speakers and aerial connections are not shown in order to help with clarity. In the case of speakers, this is a local decision as to whether they are used. They are not strictly necessary to the functioning of a rebroadcast or repeater device but one will be required if the ‘Standard’ variation is adopted as
one of the radios forms the normal comms set for the vehicle when it’s not in re-broadcast
With thanks to :Bowland Pennine MRT
Coniston MRT
Duddon & Furness MRT
Kendal MRT
Keswick MRT
Moffatt MRT
Penrith MRT
Roger Taylor, Tower Communications
Team Simoco Ltd
TMC Radio Pty Ltd
Tom Taylor ARCC Kinloss
MRMap Development Team 14/01/2009
The concept of re-broadcasting:The devices to be described are intended to act as two-way signal enhancement units to enable
radio communications into difficult-to-reach areas. To this end, a system using two simplex
transmissions on different frequencies has been adopted where the Base or Incident Command
Post (ICP) transmits and receives on one channel and the Hill-Parties do likewise on their Team
Working Channel (TWC). From this it can be seen that operation at the Hill-Party end remains
simplex for normal comms on the hill. Hand-portables can still speak to each other whilst taking
advantage of the increased area or distance coverage provided by the re-broadcast device.
The device itself is nominally mounted in a vehicle that is dynamically positioned to allow for the
translation of the Base transmission onto the frequency used by the Hill-Party and vice versa.
When using the re-broadcast unit, Base cannot speak directly to the Hill-Party radios. It must go
via the re-broadcast device hence the positioning of this vehicle is critical to operation of the
system as a whole. Having said that, it is strongly recommended that Bases / ICPs do monitor
the TWC as it is then often possible to make direct contact with a party that is not in the coverage area of the rebroadcast unit.
As originally agreed in negotiations with OfCom for permission to use such a device, it must be
clearly stated from the outset that permanent operation of re-broadcast transmitters was not
agreed by the authorities. Re-broadcast should be used to alleviate individual communications
problems on a case-by-case basis. When normal methods of communications fail. That is, when
direct communications between the Base/ICP and the deployed Hill-Party hand-portable radios is
not directly possible due to the nature of the immediate terrain and not the terrain in general.
More rebroadcast channels have been requested so that if the topography of any Team’s area
forces continuous use of a re-transmission system then they may deploy a unit on a more permanent basis. At the time of update August 2008, no additional link channels have been authorised.
We are, however, now authorised for operation of re-broadcast devices from permanent locations.
It is important that this is fully understood by any Team wishing to use re-broadcast as there are
almost certainly going to be incidences of mutual interference between different Teams during
the initial testing phase and, indeed, in their normal operational usage. Any team operating outside the conditions of use of re-broadcast devices has no redress if it receives an unacceptable
level of interference. Conversely, any team causing interference to others may well find OfCom
on their doorstep. Always bear in mind that the new ‘MR’ channels are subject to the same level
of official monitoring that is applied to the rest of the marine band.
Rob Brookes/Tom Taylor 14 January 2009
MRMap Development Team 14/01/2009
The General Principles of Rebroadcasting
As you will see in the following pages, re-broadcast is not a lot different in effect, from
manual relay. The same vehicle in the same position could handle both methods. The only
real difference is that there is now no need for the vehicle driver to relay massages to base.
The argument that manual relay takes a team member off the hill is not really valid as most if
not all teams have people who’s hill-going days are a memory rather than a fact. These people
do, however, have a wealth of understanding as to what the rest are doing when dashing up
the hill. They are to be found in the manual relay vehicles of a number of teams already.
Radio re-broadcast does not make them redundant, in fact it may well make their lives a little
more interesting occasionally. For automatic
re-broadcast to work, the vehicle must be correctly positioned. The driver of the manual relay
vehicle may well, during the course of a search for example, have to move the vehicle in order
to maintain good comms between him or herself and base whilst still being able to contact the
moving hill-party. This doesn’t change in re-broadcast and if there is any possibility of the hillparty shifting it’s position then an un-manned re-bro vehicle may become unusable. Intelligent
autonomy is required from your rebro vehicle driver, they must re-locate to a new position,
sometimes without any instruction from base. They become a very important element of your
communications system as a whole.
The job of the rebro vehicle driver, is to find the best position to establish good comms between base and the vehicle and the hill-party and the vehicle. Once this has been done, the rebroadcast device can be switched on and comms is then automatically handled by the vehicle.
However, the driver still needs to monitor the comms to ensure that the vehicle is still in the
optimum position. If not then he or she will have to advise both parties of an intention to relocate and this must be done as quickly as possible.
Re-broadcast isn’t magic, it won’t always work. All teams have places where comms are particularly bad and base will expect to loose the hill-party in such locations. If they’re just passing
through this location, it probably doesn’t matter. If the casualty has managed to crawl to the
most difficult location possible before collapsing then most of your work will occur out of reach
of comms with base. Whether this is important or not depends on a lot of factors but it probably will be.
This is what the re-broadcast system was designed for as against wide area repeaters designed to provide saturation coverage of a team area. Most Lakes and Lancs teams already
have reasonable coverage of their areas by radio, usually from existing fixed sites. We have all
had radios for over fifteen years so they aught to work by now! They don’t cover everywhere,
indeed, the laws of physics prevent this anyway. However, the positioning of remote aerials or
careful positioning of bases has resulted in generally good coverage. In effect, most teams
unknowingly have a simplex version of ‘Wide-area-coverage’ already.
MRMap Development Team 14/01/2009
What re-broadcast does is to fill in the gaps on those occasions when the main system
struggles to cope. You wheel it out in just the same way you would your manual relay vehicle.
Under some circumstances, it doesn’t even have to be a full-blown team vehicle anyway.
These devices can be fitted to virtually anything that can provide them with power as Penrith
and Bowland Pennine have both shown. Now we have it where the re-bro vehicle is not taking
out an active hill-going member of the team, nor is it necessarily tying up a team vehicle. If
the private vehicle doesn’t have a pump-up mast fitted, and how many do? Arrange with a
local farmer who lives at a well-used relay location, to put a mast on his barn and plug your
radios into it when you need them. There are always ways.
The job of the vehicle driver now becomes more critical as base can quite easily tell when a hill
-party are moving out of comms range but they will find it hard to predict just where the relay
vehicle needs to move to. That’s a job best left to the man on the ground, the driver. Relay
vehicle driver is a job probably not best left to the newest team member.
If the driver uses a handset that has been arranged to scan between the team working
channel and the rebro channel, then he or she will be able to hear both sides of the
conversation, provided by the rebro they’re operating. By the same token, the driver can also
speak to either side of the rebro by using the opposite channel on the handset. They can
become either base or hill-party depending on which it is they need to speak to.
Indeed, program the two channels to say who it is you will be speaking to and it’s even easier.
Program the radio’s display to read ‘Hill-Party’ and program the frequency as 147.350 MHz and
the driver will become base for the time being. The transmissions will be boosted by the rebro. If this is used then the handset’s power need only be a watt or less and the battery will
last forever.
By the same token, program the display to say ‘Base’ and the channel as your TWC and the
driver becomes another hill-party radio and will be heard by base via the re-bro. In neither
case does the driver’s radio need to be able to transmit back to either side un-aided. It uses
the re-bro in just the same way all others do.
The driver can now leave the vehicle temporarily without being out of comms with either hill or
Sometimes the urgency of a message can be lost when it’s passed by another’s voice. Using re
-broadcast, the margin for translation errors when passing messages is dramatically reduced
as no intermediary has to repeat them with all the inherent dangers of accidental
interpretation or inflection changes.
The intention isn’t that they are used routinely to provide base to hill communications although
the position of your team base has a lot to do with this and, for example, Duddon & Furness
have a base location not well suited to covering their whole area. Their deployment of
re-broadcast vehicles will be more than most. It’s not in the interests of avoiding interference
for us all to operate in this way but one or two aren’t going to cause too many problems if
those who don’t need to deploy them regularly, keep to that principle.
MRMap Development Team 14/01/2009
General Principles - The Old Way—Manual Relay from a vehicle
Direct communications from the base, May not be
possible with the party on the opposite side of the
hill. The signal from base will just pass over their
heads or be absorbed by the intervening hills.
In the same way, the hillparty cannot make contact
with the base.
Manual Relay Vehicle
Base could transmit to the vehicle and ask it to relay out to the
hill-party as we have always done in the past. The vehicle needs
to be manned and in the right place!
General Principles - Not in the spirit of the thing!
You could park a vehicle as high as you can get it but this is bad for relations with the neighbours and bad for the level of interference you will receive yourselves from teams in other regions who are probably operating correctly so you have no re-dress. At least one police force, Derbyshire, is actually still using
the re-bro channel so you will definitely attract some attention by using the illustrated approach!
General Principles - The New Way—Automatic re-broadcast from a vehicle
For re-broadcast to work successfully, it isn’t necessary
to take the vehicle to the top of any hills. It only needs to
be in a position where both the base and the hill-party
can be satisfactorily contacted from the vehicle.
Using the re-broadcast device, the base changes to
channel 96 (147.350 MHz). It both transmits and
receives on this channel.
Simplex comms between handsets
on the hill
Team Working
Channel both ways
147.350 MHz
both ways
Re-Broadcast Vehicle
At the vehicle, the signal received from the base is converted to the Team Working Channel.
It is then re-broadcast out to the hill-party. The positioning of this vehicle is critical to correct operation of the system. The vehicle must be able to ‘see’
both stations trying to communicate with each other however, it doesn’t always need to be manned.
Optimum Position Planning.
It’s possible with a little work, to pre-plan suitable locations for known radio black-spots. The free, on-line coverage calculator provided by
ATDI can give a coarse prediction of coverage for a given location. In the example below, a location at a view-point on the A684 Garsdale
Road gives an indication that it would permit re-broadcast from the Kendal remote site at Singleton Park, out to the Cautley Spout area where
comms are otherwise impossible.
Although this hasn’t been checked, it
does give some indication (for free) of
where we might want to begin looking
for a suitable location when working in
the Cautley area.
By using the FreeWare ‘RadioMobile’ application, much greater accuracy can be achieved when plotting optimum coverage of fixed or mobile sites.
Radio Mobile software is a copyright of Roger Coudé VE2DBE. Radio Mobile is dedicated to amateur radio and humanitarian use. Although commercial use is not prohibited, the author cannot be
held responsible for its usage. The outputs resulting from the program are under the entire responsibility of the user, and the user should conform to restrictions from external data sources.
The official Radio Mobile web page is
Radio Mobile software is free but you can help...
First Steps - The Simple Approach to Rebroadcasting.
The following information is based upon documentation published on the TMC Radio website and
research carried out by various teams.
It represents variations on broadly similar systems that increase in complexity as they go on.
Ideally a team radio officer would select the version he or she feels is most appropriate for their
own team. All the following examples work but there are explained reasons why some of the
very simple versions would not be completely practical.
“Cross-Band” Re-Broadcast.
Defined as :- Each radio operates in a different part of the radio spectrum, here, high band and low band. They therefore don’t interfere with each other.
All re-broadcast units require two radios.
One on the team working channel (TWC) and another
On the re-broadcast channel shown here as a
hypothetical Low Band (68 to 88 MHz) channel
Low Band
The various radio configurations used to form
rebroadcast devices are taken from information
provided by TMC Radio Pty Ltd in Australia.
They are the manufacturers of the ‘Simoco
SRM9000’ series radios. Rebroadcast can be
achieved using other manufacturers hardware
but the extremely simple way in which this is
achieved with SRM9000’s, and the number of
variations available for experimentation, means
they are hard to beat under these circumstances.
The two SRM9005’s require only a special cross-linking cable connected between the front-mounted RJ45 jack sockets, in order to become a rebroadcast device. The rebroadcast mode is automatically selected once the cable is fitted and both radios are switched on. See
the next page for details of the cable.
This is fundamentally the same for all variations on the system. Two radios connected by a crossover cable.
Using the configuration shown, the Team Working Channel (156.175 to 161.875 MHz) is converted and simultaneously re-transmitted on a suitable low band
frequency. 86.3125 MHz for example as is used in Scotland. Whatever the frequencies used, the system adopted is called ‘Two-Frequency-Simplex’ . That
is, two separate frequencies are used in the system, one in the primary radio and another in the secondary radio. Each radio both receives and transmits on
it’s programmed frequency hence is simplex in operation. All persons listening to either of the two radios will hear both sides of the conversation and each
other. The rebroadcast device converts one frequency to the other and re-transmits it.
The above circuit is the simplest form of this device and requires no other hardware apart from power and aerials. The operating channel of the TWC radio
can be changed but this requires that a 9025 telephone handset or a similar control head, is plugged into the socket occupied by the cross-over cable so is
obviously not a permanent feature. Basically, this device is meant to operate on one TWC only.
The Simoco 9025 telephone handset control head
and magnetic mounting plate
Very Basic Rebroadcast
There are no UKSAR low band channels available but a number of teams have now purchased their own frequencies from Ofcom for this purpose and under these circumstances, this is a viable solution to the problem.
Cross-Linked Cable
(Part Number : 9503-000-00018)
The cross-linked cable simply swaps the Tx/Rx Data lines (enabling the two Transceivers to communicate), and cross-connects the Receive and
Mic Audio lines so that the audio signals can pass between the Transceivers. You can easily make one up by splitting a short CAT5 patch cable
and re-jigging the connections.
Editor’s note:- Pin 5 on both RJ45’s is left un-connected. I believe this is not the case on the crossover lead supplied to LDSAMRA.
This diagram shows the pin-out and part number of the Crossover lead. It can be made up to virtually any length using standard CAT5 components.
From Simoco, the cost is about £12. All SRM9000-based versions of the re-broadcast device require this cable to be fitted.
Note that the two radios are placed into rebroadcast mode as soon as the crossover cable is connected.
Information taken from TMC publication - A9k-501 “Simple Repeater” available from the TMC Radio website at
Where no control head is used, as in the ‘Simple’ repeater…….
The Standard Power and
Speaker Connector (Facility connector)
Back of the power plug
The current sinking capacity of pin 8 is
around 130mA so the combined current required to switch any external devices, should
not exceed this. This can be increased using
transistor switching if necessary.
Four pins linked for negative supply lines
NO7BB 12 volt LED Green
NO5BB 12 volt LED Red
Maplin Electronics
Four pins linked for the positive supply
Simple System
On/Off Indication
Pin 8 - the programmable output
connection. (Programmed to be
Low on Tx)
Speaker connections - pins 6 and 13
Pin 3 - the Ignition sense connection. Pin 3 should be linked
to the adjacent positive supply pins to ensure switch-on.
The SRM9000 power and facility connector.
The TMC Radio ‘Simple’ Repeater
This is the simplest form of rebroadcast/repeater possible using Simoco SRM9005 radios.
Normally no speakers would be connected and there is no control head.
Because both radios operate on frequencies that are not too far apart, some interference
between the two is to be expected. Adequate vertical separation of the antenna can help here.
Horizontal aerial separation is unlikely to prove effective unless your base is in the grounds of a
medium size castle.
You are recommended to visit the TMC Radio website and to download the file A9k-501 ‘Simple Repeater’.
The High Band Rebroadcast Channels
and Vertical Aerial Separation.
This aerial significantly higher
than the other.
“In-Band” Rebroadcast.
Defined as :- Both radios are in the same radio frequency band.
In this case, both are high band.
147.350 MHz
Crossover lead
If the currently designated VHF rebroadcast channel of 147.350 MHz is to be used instead of a low band channel, then the risk of mutual interference
between the two radios is high.
This system has been made to work by introducing a degree of vertical separation between the aerials of each radio. Say one on the vehicle roof, and the
other at the top of a suitable mast. Over limited distances it does work and allows all Team Working Channels to be used. Again, channel changing is
effected by temporarily replacing the crossover lead with a control head in the TWC radio.
This is still not a fully practical solution but it does work. Being in the same band, the radios will tend to interfere with each other.
Very roughly the Diplexer works as follows;
In order that the in-band radios can operate side by side without de-sensing each other, a device called a diplexer (or duplexer) can be used. This is basically two independent filters. One is tuned to the frequency of one radio and the other to the frequency of the second radio. Diplexers are not required when
cross-band re-broadcast is used.
In the present case, one side is always tuned to 147.350 MHz as this is the common uplink channel used by all of us at this time. This is the ‘Low’ side
of the diplexer. The other radio would be programmed with your Team Working Channel, the ‘High’ side. In practice, this works a little like the left and right
channels on a stereo amplifier. The two radio frequencies are kept apart and not allowed to interfere with each other. The price you pay for this is that the
tuning of the diplexer is both precise and narrow. If it were not then they wouldn’t work!
On the 147.350 MHz side, this isn’t a problem as only this channel is required, but on the TWC side, ideally we would like to be able to use the rebroadcast
on all TWC’s. Sadly, due to the narrow tuning, this isn’t possible and the best we can achieve is that if your TWC is an ‘A’ channel as in 63a or 156.175 MHz,
then you can use your re-broadcast device on any other ‘A’ channel. The same goes for the ‘B’ channels as in 85b or 161.875 MHz. These teams can have
their rebro operate on any ‘B’ channel. When operated away from the channel for which it’s been tuned, the diplexer will degrade the performance of the
The only channel available to both types of rebro is 158.650 MHz or 53a. This is approximately mid-way between both sets of channels and would be available as a common channel should this ever be needed. It’s still not ideal and the performance of your system will inevitably be degraded.
Simultaneous receive and
transmit From a single
aerial. The Diplexer
effectively ‘steers’ each
frequency to the correct
Filter tuned to
the TWC
Aerial socket of
the TWC radio
Electrical screening between the
two sets of coils
Filter tuned to
147.350 MHz
Aerial socket of
the 147.350 MHz
A simple rebroadcast device capable of operating on your own Team Working Channel and a few others near to you would be built like this.
This is the ‘Simple Repeater’ as described in the TMC Radio publication A9k-501. The only difference is the addition of the diplexer allowing use of frequencies, in both radios, that are close to each other.
De-sensing is reduced to a very low level and only a single aerial is required. However, changing channels is no easier with this device than with any others so far
described. A control head is still required. For single channel working, ie on a team
TWC only, this configuration is all you will need.
The radio frequency signals
are ‘steered’ to the correct
radio by the tuning coils.
Crossover cable
147.350 MHz
The ‘Simple’ In-vehicle, Re-broadcast Device.
A practical, if basic, solution. In a vehicle, a separate radio would be used for normal voice comms. The above
device is only switched on when rebroadcast is needed as shown in the next section.
The TMC Radio ‘Simplest’ Repeater
This is probably the method that most teams initially looked at and the one several teams now
use. It works fine with a little training and it’s only real fault is the need for three radios and two
aerials for each vehicle. Having said that, it’s a very flexible and reliable method of setting up a
vehicle rebroadcast system and some teams may need to go no further than this.
To run the system efficiently, you do need to have the facility to switch off the pair of radios
making up the rebroadcast section. They really only need to be powered up when the
rebroadcast is in use.
The TMC Radio “Simple Repeater” The full, in-vehicle, configuration.
The ‘Practical “Simple” Repeater’ is probably the easiest to set up and get going. It can’t however, manage the normal vehicle communications task
because it has no control head. This has to be carried out using a third radio dedicated to providing normal comms. This radio is fitted with a control head
and would be at the front of the vehicle. When using this radio, the rebroadcast radios should be switched off and when using the re-broadcast, the main
vehicle radio should be switched off.
This approach is only partially successful for a number of reasons, the main one being
that it requires three SRM9000’s to make up the complete communications system for a
rebroadcast vehicle. Some teams may accept this in view of the ease with which the
system can be set up. It will certainly work as a rebroadcast device.
Two independent aerials are required.
Using a dash-mounted rocker switch to provide power to either
system but not both.
Power to the Main Vehicle radio
Positive battery supply
Power to the Rebroadcast radios
Control of rebroadcast
depends on which radios
are switched on.
Crossover cable
Secondary Rebroadcast
Independent Vehicle
Communications Radio
Primary Rebroadcast
Using the above switch
suggestion, only one
setup can be on at any
time. Either the main
radio or the Rebro can
be on, never both.
Test Rig Rebroadcast Device
This is the practical application of the circuit shown on page 17.
Possibly one of the easiest ways of setting up a rebroadcast unit for testing, is
to mount the component parts onto a
suitable board.
This cuts down the trailing wires and
allows you to fit the device into various
locations for the purpose of testing.
With a big enough vehicle, it’s even
possible to leave it assembled in this
The aerial connects to the diplexer
output here.
The black cable shown top left of the
picture is the cross-over cable. The one
supplied by Simoco is red in colour but
this one was made up for the job.
Notice that the speaker leads have been
left un-connected. Speakers can be fitted if the vehicle is to be manned and
the system monitored.
The ‘chocolate-block’ connector bottom
left is used to allow a single power supply lead to be split to two radios.
The small black box at the bottom of
the diplexer
carries two indicator lights which illuminate when the radio they are connected
to, is receiving a signal. This is a quick
way of telling that the system is operating. They are powered by the pin 8 connection on the facility connector for
each radio.
The simplest form of On/Off indication is a single LED across pins 4 and 8 on the 147 MHz radio programmed to have pin 8
go low on transmit. If the TWC radio receives a signal then the 147 radio will transmit and the LED will light. Both radios are
thus tested as ‘On’ by a single LED.
A Transportable Rebroadcast Device.
The board-mounted version shown on the previous page can be
more securely mounted and used in exactly this format as
demonstrated here by Kaz Brush of Penrith MRT. Looking like it
might take the blast from a small nuclear device, you can see it
still isn’t much bigger than the component parts used to make it
up. The case doesn’t add much to the overall volume of the
device and it can easily be moved from vehicle to vehicle.
Generally speaking, the applications are limited by
your own imagination as the basic radio system is the
same for all versions. There will doubtless be others
we haven’t covered here but hopefully the ingenuity of
teams in the North West have provided some ideas for
you to have a go at.
The TMC Radio ‘Standard’ Repeater
This is where things get a little more complicated
As already mentioned, the problem with the previous version is the need for a separate radio to
handle normal voice comms to and from the vehicle when the rebroadcast device isn’t in use.
It’s possible to have only two radios handle the job of both normal comms and rebroadcast but
you are now into the realms of additional accessory boards. With the next few suggested configurations, the level of technical complexity increases.
You are recommended to visit the TMC Radio website and to download the files A9k-821` ‘Dual transceivers using a
common control’ and the ‘MA-DMAP Option Board Technical Manual v2’
The TMC Radio “Standard” Repeater.
The ‘Practical “Standard” Repeater’ is designed to provide the missing socket needed for the fitting of a control head to the two
SRM9000’s that make up the rebroadcast section. This allows us to do away with the third SRM. It also requires some programming to be
carried out on both SRM’s in order that we can control whether the radio is operating normally or in rebroadcast mode. The DMAP board provides this additional socket, in fact it provides two additional sockets. It also provides an enhanced level of audio processing and takes care of
the repeater logic switching.
Refer to TMC Radio publications A9k-821, and the ‘MA-DMAP Option Board Technical Manual’ which gives details of programming
When switched to rebroadcast
mode, the aerial changeover
relay reconnects the TWC radio
to this aerial. Normally this
would be a pump up mast aerial
or similar.
This is the default aerial used when rebroadcast has not
been switched on.
If the primary radio has a button programmed to send the DB-15 pin 8, low
when pressed (Auxiliary) then the aerial change-over relay will operate and
switch in the diplexer. When ‘Off’, the diplexer is not in circuit and all channels can be used
The aerial change-over relay
SRM9030 internally fitted with DMAP board
Control of re-broadcast is via
the programming in both
Pin 8
Pin 4
Secondary rebroadcast
only Radio
Primary vehicle or TWC rebroadcast Radio
It isn’t necessary to program
a ‘Radio Select’ option as the
secondary radio performs
only one function. You need
only program a ‘Repeater’
Programming the ‘Standard’ DMAP Repeater
For all versions of the rebroadcast device, the ‘Minimum
Speech’ setting must be 15. Leaving it at ‘0’ will result in no
transmitted audio from your repeater.
Program one button (F3) for “Repeater Mode”.
Program F4 for “Auxiliary”. Label the button
screen displays as shown - ‘REPEAT’ and
Pressing F3 sets the rebroadcast mode.
Pressing F4 will send the power connector pin 8
high and switches the diplexer into circuit.
Again, ‘Radio Select’ has not been programmed as
normal comms are not required from the Secondary radio.
Ensure your output on Pin 8 is programmed to go
high in order to operate the transistor switch in
the diplexer box.
For portable, out-door use, Bowland Pennine MRT have encased the whole rebroadcast unit in a Peli-box.
Shown here with the internal
top-plate removed, the device
has everything self-contained
with the exception of the aerial and power supply.
This device has been deployed
on a number of occasions and
Iain at Bowland Pennine has
accumulated a considerable
amount of information as to
what you can and can’t do
with these devices.
Even though it’s a working
unit, development on this device hasn’t completed and
switched speakers are the
next move.
The current best option for display capabilities and easy of
reading, is the 9030 control head.
Also a control head option, the 9022. This incorporates
all the functions of the 9030 but in a completely handheld device. For use in Bowland’s Peli-box system, it
may have advantages when it comes to mounting and
In case you hadn’t already guessed, this is your fist mic
A recommended improvement providing a more elegant solution
to the problem.
Here, the suggestions again get a little more complex and the ability to
follow an electrical diagram is a great help.
We have to stress here that any additional assistance needed with these
configurations can be got from either myself or the contributing team.
The Modified TMC Radio “Standard” Repeater.
From work carried out by Alan Prescott at Keswick MRT, it’s been discovered that the repeater function provided by the DMAP board, is not strictly
necessary. If the crossover cable is connected to the existing front RJ45 sockets on each SRM9000, then rebroadcast mode is entered as soon as power is
applied to both radios in much the same way as it is in the ‘Simple Repeater’. It’s the ‘Both radios’ that is critical here. If the secondary radio has it’s power
provided by a switch or relay that is operated at the same time as the aerial change-over relay, then rebroadcast mode is automatic and operational at a
single button press.
If the button is pressed again, then the aerial change-over relay drops out and connects the primary radio to a straight-through aerial and removes
power to the secondary radio at the same time, switching you back to normal comms. This is an elegant solution that has a lot to commend it. The ‘default’
condition, should the relay fail to operate, is normal, all channel, comms. The DMAP board is needed only for the additional sockets it provides and the
cheaper MA-ASIG board can also be used.
If required, a second control head can be connected to the remaining DMAP RJ45 so giving the two heads required by some teams, plus rebro.
Connection to the vehicle power supply
Power is switched to the secondary
radio, only if rebroadcast is required
Power Relay
Permanent power connection to the primary radio
If the primary radio has a button programmed to send the DB-15 pin 8, low
when pressed (Auxiliary) then the aerial change-over relay will operate and
switch in the diplexer. When ‘Off’, the diplexer is not in circuit
SRM9030 fitted with DMAP board
Pin 8
Pin 4
Secondary Radio
Crossover cable
Primary Radio
A second control head
(of the same type!) may
be fitted elsewhere in
the vehicle if needed.
Programming for the Modified TMC
Radio Repeater
The output pin DB15-8 is programmed to go
High when button ‘F3’ is pressed. Alongside this
button, the screen display will read “REPEAT”.
When Rebro is active, this will be preceded by a
The remaining programming options
need no alteration as the DMAP board is here
being used only for it’s available RJ45 connections, it doesn’t handle the repeater functions
at all.
Manually Switched Rebroadcast Mode
Probably the easiest and most efficient method of implementing
vehicle comms and rebroadcast from a pair of SRM9000 radios.
This configuration doesn’t rely on programming of the radios in order to achieve
switch-over from standard vehicle comms to rebroadcast. Instead it uses a basic
change-over switch which, when operated, powers both the secondary radio and the
aerial change-over relay. It requires only a switch on the dash of your vehicle which is
labelled ‘Normal Comms / Rebroadcast’ or however you want to phrase it.
For it’s ease of implementation and use, this method has a lot to commend it.
The Modified TMC Radio “Standard” Repeater , alternative suggestions.
The MA-ASIG Board
As the repeater function is now being provided by the crossover cable and not by the DMAP board as in the previous example, it is possible to dispense with this board in favour of the very much cheaper MA-ASIG board. This, again provides the necessary additional socket required in order to fit a control head. All other connections remain the same. The standard configuration for the MA-ASIG board does not support this facility and anyone wishing to use these boards must order the MA-ASIG board for use in a ‘Dual-Control-Head’ configuration.
There is a very significant price saving to be made in the use of these boards over a DMAP although in the configuration shown, a DMAP
board can be used without any changes if you wish or already have one.
The specification for the MA-ASIG board is contained in TMC publication A9k-465
Power is switched to the secondary radio, only if rebroadcast
is required. The aerial change-over relay is powered at the
same time switching the diplexer in.
Using this method, no programming of the radios for repeat
mode is required. Everything is handled by the crossover
cable and the On/Off switch.
Normal Comms Aerial
(Vehicle Roof)
Re-Bro Aerial (Mast etc)
Dash-Mounted On/Off Switch
Connection to the vehicle power supply
Permanent power connection to the primary radio
SRM9030 fitted with MA-ASIG board
Co-Ax Changeover relay
No additional programming
of the radios is required and
both radios enter rebroadcast mode if the dash switch
is operated. Normal operation is returned to the main
radio if the switch is Off. All
team working channels are
then available.
Indication of the rebro
being active can be by
using an illuminated
Secondary rebroadcast Radio
Crossover cable
Primary vehicle or rebroadcast Radio
Although a much easier solution, the previous example was still
complicated by the fact that the diplexer needs to be present to
keep the frequencies in each radio, apart.
If a cross band system is used where the rebroadcast link from the vehicle to the base
is on a different band, the old low band channels being the most obvious for experimentation, then no diplexer is needed and the system is very much simpler to setup.
In the example shown on the next page, a button on the control head has been programmed for and Auxiliary output on Pin 8 of the power connector. This method can
easily be replaced by the dash-mounted switch shown in the previous example but as
there is no diplexer relay to also be operated, only one button needs to be programmed to switch the system on and off so this is probably the more elegant solution
The Modified TMC Radio “Standard” Repeater, alternative suggestions.
The Low Band Uplink
It’s clear how much simpler the low-band uplink channel would make life. The need for a diplexer and aerial switching is completely removed although the vehicle will still require two aerials, one low band and one high band.
This is the option chosen by some of our colleagues in Scotland and there is a lot to be said for it’s use by English and Welsh MRT’s. At the
time this document was produced, no such low band uplink channel is available south of the Border but a number of teams have bought their
own from Ofcom.
Base operates on the low band
channel and the hill-party remain on the TWC
As in the previous circuit, a dash-mounted switch can be used instead of a
relay, no programming is then required.
Connection to the vehicle power supply
Power is switched to the secondary radio,
only if rebroadcast is required
Power Relay
Permanent connection to the primary radio
If the primary radio has a button programmed to send the DB-15 pin 8, low
when pressed (Auxiliary) then power is supplied to the secondary radio
placing the system, automatically, into rebroadcast mode
Two aerials are again required in this
configuration. One Low Band and one
High Band.
SRM9030 fitted with MA-ASIG or DMAP board
Pin 8
Low Band
It isn’t necessary to program
a ‘Radio Select’ option as the
secondary radio performs
only one function. You need
only program an ‘Auxiliary’
button to send pin 8 low.
Pin 4
Secondary Radio
Control of rebroadcast is via
the programming in both
radios unless the switch option is used.
Crossover cable
Primary Radio
Extending the Capabilities of the Standard Repeater.
At this point there are hopefully enough options for you to select one you think will suit
the needs of your team. Most of those requiring buttons to be programmed on the
control head can also be used with simple dash-mounted switches. It’s perfectly possible to mix and match the methods used in each of these examples. This is already a
large document, there wasn’t room to include all the variations!
If you’re happy with one of the suggested solutions then I’d strongly recommend you
get it up and running before going any further. The next section includes some additional suggestions for enhancing what you now have, hopefully, a working, vehicle
mounted, rebroadcast system.
Additional Variations Applicable to Most of the Devices shown so far. -
Selcall Control
Setting up selcall (Selective Calling) is a topic in
it’s own right and anyone who wants more detail
is advised to contact the teams where work has
been successfully carried out with this system.
Contact details are at the end of this document
If the programmed relay option is used to provide
power to the secondary radio so setting rebroadcast mode to ‘On’, then this can be arranged
via selcall as shown here. The facility connector
pin 8 will now go low switching the system to rebro, on receipt of a selcall sequence “12345”.
A second selcall sequence provides the
‘Repeater Off’ function
Note that the system
replies to you using the
Encode sequence programmed under
‘Encodes - Encode 1’.
This can be anything
from a simple beep to a
sequence which triggers
a message on your
handset telling you the
system is on. The variations are endless but the
time taken in setting
them up needs to be
considered before you
embark on this.
Dave Binks at Duddon & Furness has designed and adopted a system where both radios can be independently used on all channels and a significant level of
control via selcall is available. Individual rebro vehicles may be remotely activated and the user is advised as to which rebro he or she has just switched on.
Operation of the system is best left to his own words and the following section has been supplied by Dave.
His diplexer requires modification beyond that already undertaken, on our behalf, by Roger Taylor and a picture of the finished article with the lid removed,
is shown below.
Dave’s modifications involve the fitting and control of an additional relay but the functioning of the device is still based upon the TMC DMAP repeater that
has been enhanced by both software and hardware mods. This is the most sophisticated system we currently have available to us and the needs of each
team as assessed by the radio officer will fall somewhere between the very simple and the version shown here. It all depends on what you think your team
can handle successfully as someone’s life might really depend on the proper functioning of these devices! Build what you think your team can cope with.
Rebroadcasting to most radios officers was a challenge, but to the average team members it meant absolutely nothing. After a little education, most then
realised the benefits, although that was as far as many wanted to go. They were not interested in how it worked as long as it did. With this in mind, and
the fact that we have large parts of our area that are not in radio range of the base without rebroadcasting, my aim was to make the system as easy to use
and as idiot proof as possible thereby gaining the widest acceptance and subsequent usage by all team members. There are signs that I have achieved this
aim, as a good number of members are now confident with their use.
There follows a section detailing what each group of team members needs to know (Hill party, vehicle and base groups).
Note: I use “repeater” and “rebroadcast” interchangeably in this document, although I am told it should always be “rebroadcast”!
Hill Party
The hill party does not need to know anything. This is common to all the repeater setups providing the rebroadcast channel is used for the “base to the repeater” jump and the TWC from the rebroadcast unit to the hill parties.
Although it will usually be the base that controls the repeater, to allow flexibility, I have programmed one of the buttons on the side of the radio to enable a
hill party to switch on/off one or other of our repeaters. This is all done through a single “control button” which is explained later.
To ensure that the repeaters can be remotely controlled, when leaving a vehicle the radio (single control head) must be left on, and the right hand radio
(see later for explanation of this) must be on the TWC. This is the usual operating mode. If a team member is unsure if this is the case, then switching the
radio off then back on will bring it into the required state. There is no requirement to change any aerials over or switch any additional radios on.
When the repeater is on, the control panel in the vehicle displays “Repeater” and all keys are disabled except for the manual repeater control button (the red
one below the on/off switch) and the On/Off switch.
The LED above the On/Off switch also flashes between red and green. I added this during development so I could see if the DMAP board software was run33
ning and decided to leave it in!
(Continued on page 34)
(Continued from page 33)
As described previously it is envisaged that base has overall control over selecting which repeater is required, changing them as required by hill party movements.
Switching a repeater on is achieved by pressing one button on the base radio, once for repeater 1, twice for repeater 2, three times for repeater 3 and four
times to turn them all off, then change the base radio channel to Rebroadcast. When a repeater comes on it sends a number of beeps back to the base on
the TWC, 1 beep for repeater 1, 2 beeps for repeater 2 etc, so that you know that it has come on.
Note: If any repeater is turned on all other repeaters automatically turn themselves off to prevent repeater lockup. i.e. If repeater 1 is on, and repeater 2 is
turned on by pressing the repeater “control button” on the base radio twice, then repeater 1 will automatically go off. When a repeater is switched off, it
sets both radios back to the channels that they were on and the display returns to normal.
The “control button” button I am using on the handsets is one of the buttons on the side of the radio and on the base station it is the “=” button (labelled
on the screen as CntRpt). It can be any button, including the numerical ones.
I have also set the repeater to broadcast its identification (1 beep for repeater 1, 2 beeps for repeater 2 etc) every 5 minutes to remind and reassure the
base operator that the repeater is still on, in range and functioning correctly. This transmission is on the rebroadcast channel so hill members don’t hear it,
and is inhibited if there is radio traffic at that time.
Both radios and/or the repeater can be used on the move.
Using the diplexer gives the repeater a range as good as a standard base set (as there is no desensitisation from the transmitting radio), so in theory the
distance from the base to hill party can be twice the normal radio range and go around a corner.
This configuration does not suffer from the power on problems
(Continued on page 35)
(Continued from page 34)
Technical Details
Two independent radios
When not in repeater mode you have 2 independent radios that can be used on all the SAR frequencies via the single control head. The head can be
switched from radio to radio by pressing the top button on the radio – it’s labelled on the screen with an arrow pointing to the radio that it is currently controlling (“left” or “right” hand radio).
Why 2 radios?
1) When the radios are turned on (single switch on the control head) the default state is the right hand radio on the TWC and the left hand one on the ECC
channel thus complying with the requirement to monitor this channel (Although I believe this requirement is to be relaxed?).
2) When working with other teams (and coastguard) you can keep general chitchat on your own TWC while still monitoring and operating on the other
team’s (or coastguard) channel.
3) When attending an incident, if expecting a helicopter (or even if you’re not), you can monitor CH53 as well as the TWC.
4) We don’t always man base during an incident because we can’t always get radio contact, even with repeaters, back to base from all areas. So we use
one of the vehicles as a mobile base giving us 2 radios to control an incident.
5) If you get bored during a callout you can put one radio on scan and the other on the TWC.
The setup makes best use of the 2 radios that you need to have installed to make a repeater.
How it works – The DMAP board
The main function of the DMAP board is to supply a mechanism to enable a user to supply addition code for installation in the radio. The code is written in
“C” and compiled into a single file that you upload to the DMAP board using the now familiar radio programming software. You go to menu Options, then
Upgrade Software, select the new file and hit download. It does not change the DMAP or radio software, just adds a bit of your own.
When the additional code is installed, it gets called every 2 milliseconds. During each call you then have complete control over both radios and the head for
as long as you need, usually no longer than a few milliseconds is required to send commands and check the status of each radio and the control head. This
is when I am able to intercept selcall control sequences, intercept key presses, change the radio channels, write text to the control head display, switch the
digital output used to switch the RF relays in the diplexer box, set the volume, enable the repeater mode and send out additional “beeps”. Simoco were
very helpful (after I had finished what I wanted to do) and have sent me source code for the repeaters mode.
Further work
1) Add a "This is going through the repeater beep" to all transmissions that go through the repeater.
2) While in repeater mode, monitor another channel (eg Helicopter), and send out a beep on the TWC if any thing is heard on this channel. The base can
then switch to that channel. I could get the repeater to rebroadcast on this channel but I am not sure this is a good idea!
3) Get it to change channel remotely, i.e. use CH53 or indeed any channel in the correct range instead of TWC.
4) There are many other things that can be done, I just have not thought of them yet.
A Remote Channel-Changing Fixed Repeater System designed To
Remove The Need For Leased Telephone Land-Lines.
A number of teams in the Lakes use remote radio sites that are controlled over a
leased telephone line. These have been found to be both expensive and prone to failure from all manner of events from lightning strikes to a not so gentle shove with an
earth-mover. Because of this I looked at methods of using a radio link rather than a
land-line. Microwave links are expensive and so are not covered here although if any
team has any documented information on their use, I’d be happy to include it for you.
The chosen method was a closed, simplex link channel which can be anything you
have a license for that is not in the same band as the UKSAR channels, here I mostly
use the low band channels between 71 and 86 MHz although I have used UHF
channels with equal success but not over the distance afforded by low band.
As in the system developed by Dave Binks, this uses modified radio software not normally available but it can be arranged by contacting Rob Brookes.
The primary radio setup for the team Base
It’s important to understand that
the radio used at your base is on
a single low band channel. It
can’t be used for direct comms to
your portables on the hill. You
should always have a ‘local’ high
band radio on the UKSAR
channels, nominally this is used
to monitor channel 62a.
All normal communications with
your team are via the link
channel up to your remote site,
they, however, operate entirely
on the UKSAR team working
channel allocated to your team.
Using special firmware, the low
band radio at your base is able to
effect channel changes to any
channel programmed into the
high band UKSAR radio at your
remote site. Effectively your base
operator is sitting at a control
head connected directly to the
remote site radio. The selcall
sequence sent by the base radio
is received by the low band hill
link and the new firmware
converts it to a MAP27 channelchange instruction. As far as the
remote high band radio is
concerned it’s directly connected
to a control head that has just
told it to change channel.
The base operator’s 9030 control head. This would be
mounted in the control/radio room as required
A low band SRM9030 programmed for multiple instances of 86.3125 MHz
and Selcall
The radio complete with power supply and
speaker as it would appear in your base.
Low Band
The Main Programming Configuration.
This configuration will only work if the correct firmware files have been loaded into the SRM9005 radios.
These are non-standard upgrade files and are available from Team Simoco Ltd
Under the heading ‘Mask’ the last three digits are the channel associated
with that selcall sequence. When the Base radio is set to ‘Kendal’ then
the sequence 123C101 is sent, that is, Channel 101. To change to Langdale’s channel. Select ‘Langdale’ on the Base radio display and press the
green button on the control head. The selcall sequence 123C103 will be
sent on exactly the same frequency as before. The remote HB radio will
change to channel 103. (103) Voice is sent up the radio link with no other
signals present and should be close to the normal audio quality.
A single frequency (here 86.3125MHz) is programmed repeatedly into the
Base radio. Each occurrence of the frequency is given a different name.
That name being either a team or other use of the channel, G2A , ECC etc.
Each ‘channel’ has a different selcall sequence attached to it and although
every channel is on the same frequency, each one sends a different
selcall. This is the manner in which the channel-change instructions are
sent to the remote site
Options that could be used at Base
A second control head that offers
full control of the remote radio
from a location other than the
control room. Extension leads are
available to give up to 100 metres
A desk top ‘goose-neck’ microphone is available for the SRM9030
to replace the standard fist microphone
Fitted inside the base
for example:A DMap board would allow external devices to
be added to the base radio.
GPS Automatic vehicle location.
The Equipment At The Remote Radio Site. Two Simoco SRM9005 Radios, No Control Head
High band SRM9005.
Programmed with all
UKSAR channels
required. The
programming order
must be the same as is
in the Base radio.
High band
Low band SRM9005,
no control head.
This radio receives
the selcall sequences
from base. It serves
only to pass them on
the high band radio.
Low band aerial
This set doesn’t
change channel.
Standard Simoco Cross-link cable
plugged into the existing control
head socket on each radio
Because a cross-band system is used where one radio is on a low band channel
and the other on high band, no diplexer is required. This means all UKSAR
channels are available to be used and there is no mutual interference between
the two radios.
The selcall sequence
received from the low
band radio is used by
this radio to change
the high band channel.
The low band radios
serve only as a link to
carry the channel
change selcall sequences and the Rx
and Tx audio for the
high band radio. Anything transmitted on
the Base low band set
will be rebroadcast by
the remote high band
Moffatt MRT’s Suggested Rebro System:
The following suggestion came from James Coles of Moffatt MRT and has considerable merit for it’s stated purpose. Eventually a significant
number of teams will be using these devices and the chances of mutual interference goes up accordingly. Any means by which we can reduce
this risk will increase the usefulness of the re-broadcast devices and allow more than one team to operate simultaneously with others with the
minimum of interaction.
James’ objective is to try and eliminate the possibility of 147.350 opening other team’s repeaters.
His system requires that you program the repeater as a duplex unit with one radio only receiving on the TWC whilst the other would only
transmit on 147.350.
The base would monitor both the TWC and 147.350 but would only transmit on the Team Working Channel. Care would need to be taken to
avoid acoustic feed-back here.
The hill teams would work on the TWC and if they chose could have 147.350 as a receive only channel to listen to the repeater output in their
scan group. Teams would only Tx on the TWC.
This way if another team was deployed using their repeater the only interference would only be from the repeater and this would only open
up the base radio monitoring 147.350 and anyone on the hill monitoring 147.350. With correct placement two repeaters could be deployed
using different TWC with no fear of inference.
147.350 could be easily dropped from the scan group and revert to simplex communications on the TWC without any coordination required.
The advantage of the system shown on the next page:
If the Rebro unit fails back to back will continue function back to back where there is coverage.
Hill parties can take advantage of the repeater to talk to teams non line of sight via TWC.
Nobody needs to leave the TWC to transmit on another channel this is simple and safe.
As the only device Transmitting on 147.350 is the repeater then other re-bro units in the same locality could use the channel too with correct repeater positioning and thought.
The Schematic for Moffatt MRT’s suggested system.
Any signals received by the rebro vehicle on the TWC are re-transmitted back to the base. Both the hill-party AND the base operate on the TWC. Although
the 147.350MHz frequency can be monitored by the hill-party, it isn’t necessary for them to use it. Control of the audio output levels on both base radios
would need to be good to avoid howl-round and a head-set would probably be better suited than loud-speakers. Each ear-piece of the head-set would provide audio from only one of the receivers. PTT is only required by the TWC radio.
The hill-party transmit and receive on the
TWC but have 147.350MHz Rx only in a
scan group.
Base transmits on the TWC but
monitors 147.350MHz on Receive
only either by scanning or by using
a second receiver
Radio A
Rx Only on
Radio B
Tx Only on
James’ system is interesting from the point of view that in Scotland, they’ve not used low band and never did have as many channels as we in
the Lakes ended up with. As he points out in the accompanying emails, getting his colleagues to change channels is not as easy as we will find
it as it has no historical precedent. As such, his system is very much geared to no one having to change channel but the method operation is
not something we’re used to. Having now had it explained to me, it’s a perfectly viable system. Just one that we don’t happen to use down
This works in the Borders but might be strange to us just as our system(s) would take some explaining to James’ colleagues. It goes to show
just how much of a difference can exist but then again, having worked for many years with Lakes MRT’s, I already know that!
James’ system is no less workable than any we’ve come up with, the critical factor for them all is that there has to be an access point for an
‘outside’ team or agency. We’re none of us quite at that stage just yet and in practice, probably only time will tell whether we are all going to
be compatible on a major incident.
What will be more critical before then but wasn’t intended to be a topic covered by this document, is that we at least all understand the differences in teams who have adopted the new systems in slightly differing ways.
This is one of the reasons that Tom considers monitoring of the ECC so important and it has to be said that having now seen examples of
communications methods from teams spread over a not insignificant portion of the UK, I think he may well be right! My own team, Kendal,
has a repeater that works but is not available to Langdale team whom we regularly support due to technical problems not easy to get round.
We will got over all the hurdles and any team’s major priority is it’s own area and casualties. No one is about to dictate how you go about that
because you’ve all been doing it for enough time now to know if you’re doing it right!
All we can ask is that an open mind is kept on the ideas of all and that these ideas are not kept from others who might benefit from them.
Now that IS the purpose of this document!!
An alternative approach to rebroadcast systems in team vehicles
This method uses the additional facility terminals available on the main power
connector instead of the standard crossover lead. This leaves the radio RJ45 port
available for other tasks if required.
This group of 4 connections
are used to provide the facility
connector rebroadcast
The pin 3, ignition sense contact
Normally associated with power and loudspeaker connections, the 15 pin D connector
can also provide audio in and out plus two programmable pins, one, an input and the
other an output. These can be programmed to go either logic high or low when certain
conditions arise. These two pins can be programmed to facilitate a cross-connected
PTT arrangement where one radio receiving a signal forces the other to go to transmit
and with cross-connected audio lines, anything received on one radio is re-transmitted
via the second.
The circuit on the following page shows how this can be achieved.
An Alternative Approach To Rebroadcast
Rebro Channel Radio
Normal Vehicle
Pin 3 to Pin 4
Ignition Sense
Pin 3 to Pin 4
Ignition Sense
TWC Radio
Rebro On/Off
The connections between Pins 14 and 15 on both D-15 connectors should
be made using screened cable. The screen is then connected to the negative
supply pins.
The ignition sense connection between pins 3 and 4 is sometimes necessary
To ensure that the radio switches on when power is applied. When used in a
repeater or rebroadcast configuration there is no control head which would
otherwise indicate this.
No connections are required to the radio RJ45 ports and the red, cross over
cable is not used in this configuration. If required, GPS tracking at the
repeater vehicle is handled by plugging the computer into the RJ45
connector on the TWC radio.
If required, a control head can be fitted to the TWC radio via the
RJ45 port. If the power supply to the rebro channel radio is
switched, then the system only enters repeater mode if this switch
is on. If not then the primary radio functions as normal. The
operator must take care that the TWC radio is actually on the
team working channel before rebroadcast is switched on
If both a control head and forward control GPS tracking of team
members is required then an MA-ASIG accessory board configured
for dual control heads should be fitted. The control head is plugged
into the MA-ASIG board and the tracking computer is connected
via the radio RJ45 port.
The picture on the left shows the whole rebroadcast setup with the lid off. The radios are
standard SRM9005s but are fitted into a TSF2000, 1U, case and not in their normal
individual aluminium boxes. The necessary heatsink is on the bottom of each radio. The
RJ45 port on the left-hand (TWC) radio is connected to MRMap running on my Eee PC
and the device to the left of the computer, is the diplexer.
The image above is a close-up of the power/facility connectors. The heavier black lead
between the two D-connectors carries the cross-over connections that duplicate the job
normally handled by the red, RJ45 crossover lead. Both RJ45 connectors are available
for use with either a computer or a control head.
The completed demonstration repeater/rebroadcast unit. This is a multiple use version of the device and is unlikely to actually be
built like this for real use. However, for demonstration purposes:Fitted with a telephone handset (9025) controller the TWC radio can be used as a normal voice channel set in a vehicle. A direct
contact from the radio to the antenna is needed in this instance and this would be provided by an antenna change-over relay.
In some cases, it may be advantageous to fit a
controller to a fixed, remote site as it allows local
control of the radio should this ever be necessary. A
telephone handset is used as this is the easiest way to
provide receive audio in the absence of a loudspeaker.
This is only possible because the cross-over functions
have been provided by the facility/power connector
and not the Simoco cable that normally fits in the RJ45
sockets. These remain available for use with
controllers etc. Here they have been extended to the
outside of the case to make things easier
The switch marked ‘Rebroadcast On’ supplies power to the secondary radio so turning the device into a rebroadcast unit or
repeater if a suitable config file has been loaded into the radios. If this switch is in the ‘Off’ position then power is only supplied to
the team working channel radio. No control head or speaker is connected to the rebroadcast channel (147.350MHz) radio.
The LED marked ‘High’ is indicating that the TWC radio is receiving a signal. Because the Rebroadcast switch is on, this signal is
being re-transmitted on the rebroadcast channel. When base replies, the other light (Low) will be on. The red LED in the centre
indicates that power is on to the TWC radio.
The rebroadcast switch would also be used to provide power to the antenna change-over relay to switch the diplexer in and out of
circuit. The switch itself would ideally be mounted on the dash-board of the vehicle but could be left on the case of the unit if
required. Simple in operation. If the big green light is on then you’re in rebroadcast mode. If it’s not then you have an ordinary
team working channel radio that is controlled by the telephone handset. This is more likely to be a 9030 control head if the device
was part of a vehicle system.
If the normal style of case is used then accessory boards can be fitted. As the repeater/rebroadcast function is now handled by the facility connector and not
the RJ45 sockets, these remain available for anything else you might want to fit. If a dual control head MA-ASIG board is fitted then both a control head and
a computer can be connected. If a Dmap board is used then you have three RJ45 ports available which gives you the ability to fit a computer and two control
heads if you need to, in a forward control vehicle for example.
To work properly, the second, 147.350 MHz radio, should be fitted with an independent power switch to enable it to be switched off when rebroadcast isn’t
required. This leaves the normal TWC radio available for standard comms. If the diplexer is fitted with an antenna changeover relay then any of the usual
rebroadcast configurations can be used to switch antenna between roof or mast . Using this method, a contact pin on the power connector isn’t needed to
achieve the antenna switching. The antenna relay can be powered up by the same switch that switches the secondary radio on so that as soon as the
rebroadcast system is powered up, the antenna is switched across to the one on your pump up mast etc.
If a cross-band rebroadcast device is used and is connected up in this manner then a diplexer isn’t required and any channel on the TWC radio can be
selected and used for both normal comms and rebroadcast. The low band link radio is only switched on when rebroadcast is needed.
The same antenna changeover relay can, incidentally, still be used without the diplexer if you need to transfer the antenna to a mast-mounted one when the
rebroadcast device is switched on.
There is a small amount of programming needed to use the SRMs in this way. Both TWC and the 147 or low band link radios are programmed in this way.
Here I’ve used ‘Carrier Detect’ but if you use CTCSS or Selcall muting then you should select ‘Valid Signal’. The methods described here have been tested
and proven to work but not every possible configuration of hardware and software has been tried. I’ll continue with this and update the post as new things
are tried.
The rebroadcast version of this setup has been tested using CTCSS on both receive and transmit for all radios. Voice and GPS data both passed through the
system at range without any apparent difficulty. The current operating frequencies are 147.350 MHz for the rebro link channel and Langdale’s team working
channel of 156.175 MHz. These channels are not as far apart as some others are and the level of channel separation afforded by the diplexer allows a
significant range to be achieved even when both radios are running at 25 watts transmit power. The significant advantage of this setup for fixed site use is
that only one high band antenna is required at the remote site. In the Lake District, we are blessed with some very obliging farmers, landowners and residents
all of whom are helping to provide teams with remote antenna sites. However we are eternally mindful of the fact that we live and operate inside a national
park where planning restrictions frequently make their presence felt. The ability to get a radio linked remote site running using only the antenna that’s already
on the mast, is a big advantage.
Half Duplex Operation Using the 155.350 MHz and 147.475 MHz Pair
Base Tx on 155.350
and Rx on 147.475
Hill-Party Tx on 155.350
and Rx on 147.475
Radio A
Programmed Rx
only on 155.350
Radio B
Programmed Tx
only on 147.475
Portable radios would need to switch to a simplex TWC for handset to handset comms. Using this method, portables cannot normally speak directly to each
other. Repeater defeat can also be programmed onto one of the buttons to allow direct comms between portable radios.
That’s basically as far as the current design section goes. We haven’t covered everything that can be
done and we probably never will but hopefully there’s enough information in these pages to help
others gain the best from their systems or even to inspire someone to come up with a better one!
If that happens, I hope that you will send the details along so that we can share out the information
amongst all the teams.
All that remains is a section containing some general information and the contacts you need to speak
to in order to get further information.
Summary and Additional Information
A Swift Summary
A number of the circuits shown in this document are not really practical for reasons explained on that page, however, they would all work as rebroadcast
devices as the fundamentals of operation are adhered to throughout. Two SRM9000 radios and a crossover cable.
The idea is that practical circuits have been provided for those who can follow them and hopefully, enough detail is there to stimulate questions from those
who can’t. The intention isn’t necessarily that anyone slavishly follows the circuit chosen although there’s nothing to stop you doing that if you wish.
You will see from the diagrams that not all possible combinations have been described. Where I describe programming and a controlled relay, a dashmounted switch can often be used instead. In most cases, you can use whichever method you prefer.
As far as I can see, just about any combination of operational usage can be applied to any of the circuits. There are elements of programmed control and
facilities, or selcall control, that can be used alongside a purely mechanical on/off arrangement. You can select the options you would like to use or the ones
you think your team will be happy with, and speak to the person(s) responsible for that version for any details you need, or clarification as to whether something different might work.
There is now a lot of practical expertise available to us, we only have to make use of it.
This document isn’t by any means definitive. It’s primary purpose is to show you what has been done with the equipment that, by and large, we already
have. The level of complexity at which you decide to stop is up to your judgment of how it will be used by your team. None of the variations are necessarily
‘better’ than any other as they all use the same basic principle. In fact if you examine it very carefully, you’ll see that the fundamentally most important component in all the versions, is the cross-over cable consisting of seven wires and two plugs. Without one of these, none of the re-broadcast devices would
Pick whichever one you think your team can operate and, between us all, we have the expertise available to get it going.
Even all of this is only the beginning, Voice over Internet Provider (VoIP) is not only used to make telephone calls. Try looking at and
you will see that even the humble PMR446 radio with a nominal range of about 3 kilometres can be used to talk to anywhere in the world. Radio amateurs
already use the ‘EchoLink’ and D-Star systems to do the same thing. Communications is changing rapidly and the days of the simple analogue radio may well
be numbered. However, that day hasn’t arrived just yet and there’s still a lot that can be achieved if it’s not the rest of the world you want to talk to!
Notes and things to be aware of:1...The alternative front panel supplied with the DMAP board and carrying the 25 pin ‘D’ connector, does not need to be fitted if
the facilities available on the 25-pin connector are not going to be used. Don’t fit the ribbon connection to the DMAP board and
use the existing front panel by knocking out the pre-cut covers over the RJ45 connections. This takes up less space when you’re
trying to sort all the connections out inside your vehicle. It also makes re-assembling the radio a lot easier as you don’t now have
to stuff the 25 way ribbon cable inside.
2...The DMAP board can be fitted with a GPS receiver for those wishing to experiment with automatic vehicle location (AVL). No
additional programming is necessary. The MA-ASIG board can also take a GPS and then becomes known as MA-ASIGF. Unfortunately the control head and the GPS both need the same serial port and the board only has one. However, if anyone intends to
build up a GPS receiving system in their base then an MA-ASIG board without GPS will provide the necessary connection to the
computer. DMAP boards are about four times the cost of an MA-ASIG board. An MA-ASIGF board can also be fitted to a vehicle to
allow GPS tracking with a standard control head fitted.
3...If you are doing any modifications to the box containing the diplexer and aerial change-over relay, note that Roger Taylor who
built them, fitted a drilled, Perspex spacer under the relay. This is because the screws used are slightly too long and without the
spacer, will pass through the mounting plate and straight into the coil winding of the relay. Very bad.
4...If anyone wants to fit the suggested power relay to provide controlled switching of the secondary radio, Alan Prescott at Keswick fitted a small one inside the power plug shell, extremely elegant. You can also fit a larger one into the existing diplexer case
alongside the aerial relay.
5...If the suggested circuit for the modified ‘Standard’ repeater is used, remember that a transistor switch has already been fitted
to the aerial relay. In this configuration, it’s not necessary and can be removed with care. The pins it’s connected to are the ones
you connect to the power plug pins 4 and 8. The relay should be fitted with a back-EMF prevention diode wired as shown in the
diagram following. This stops the voltage generated by the collapsing magnetic field, when the relay is switched off, from blitzing
your radio's sensitive parts. If you use a dash-mounted switch to provide power, you don’t need the diode.
Vehicle Positive Supply
IN4001 Diode
Protection Diode when a relay is used.
Switched supply to the secondary radio
Negative supply via pin 8 on the power connector
6...There is also room in Roger’s box, to fit one of the suggested Maplin or CPC relay ‘cards’. These are usually negative voltage
triggered and their input pin just connects to pin 8 of the radio power plug. They come equipped with suitable relays usually and
would make the job easier. Fitting a long-period timer at this point would allow the rebroadcast to switch itself off after a pre-set
period of time. If this is used, it could be re-activated using a selcall sequence that just needs to provide a trigger pulse to the
timer input line.
7...CTCSS or ‘tone-mute’ is permitted on the rebroadcast channel of 147.350 MHz only. A single tone of 218.1 Hz is also allowed
on the Team Working Channels (TWC). There are conditions under which we might need to use CTCSS but they haven’t yet
8...In the TMC ’Standard repeater’, the original RJ45 socket where the control head is normally connected, is not used when a
DMAP board is fitted. As the radio can’t be programmed via the DMAP sockets but they can do everything else we require, leaving
the original socket empty allows it to be used for programming the radio without first having to unplug something else. Unfortunately this doesn’t work with modified rebros as the original RJ45 sockets are the ones we need.
9...Don’t forget to program your ‘Minimum Speech’ setting to 15 on all radios used in any of the rebro systems or
you will get weak or no audio from the rebroadcast transmitters.
10...If programming radios for rebroadcast, please remember that the Team Working Channels are programmed at a channel
spacing of 25 KHz whereas the Rebro channel 147.350 MHz is spaced at 12.5 KHz.
11...A mast of some sort used to augment the existing roof height of the vehicles does provide a very significant increase in the
performance of these devices. The operationally easiest of these masts is the pneumatic, pump-up, variety although there are
others. A suggestion is that where possible, the aerial is permanently fitted to the top of the mast as this makes life very much
simpler when trying to find a suitable location to park the vehicle when it’s in use. A test transmission can be made from the vehicle using the rebroadcast system without needing to extend the mast. Indeed, if adequate comms exist using the rebro without
the mast extended, then don’t bother extending it. The whip aerials we all use on our vehicles come in a form that allows them to
be fitted to the top of a mast. These are called ‘Ground-Plane’ aerials and usually have a standard vertical whip section and a set
of three horizontal helicals that substitute for the missing ground plane, usually the metal roof of the vehicle.
Left is a standard ground plane aerial manufactured by Panorama and
is only slightly higher than the normal vehicle mounted whips. It’s performance is good and it can be left mounted on the collapsed mast
when the vehicle is returned to base. If you are lucky enough to be
able to drive it into the garage then it can be left fitted permanently.
If you choose this option then it’s a very good idea to use a proprietary
thread fixing agent, Locktite or similar, on the helicals as this will help
to keep them in place. Operating this type of aerial without the ground
plane elements isn’t recommended!
The supplied nylon wing-nuts need backing up with locking nuts for
The BNC is probably the worst type of RF connector you could wish for
on a system that is subject to movement and vibration. Eventually the
central pin will splay out the contacts it sits in and the assembly will become electrically noisy. There’s nothing you can do about this apart
from securely binding the connections in place with self-amalgamating
tape or similar. BNC connectors are NOT water-proof!
12...Although there have been no instances reported of this happening, a problem that can occur with repeaters built along these
lines is that both transmitters lock in transmit mode simultaneously. This causes permanent ‘dead-keying’ on both frequencies and
will badly effect your comms!
A crude but effective way of making sure this doesn’t happen, is to fit a single, 8 to10 Amp, self-resetting fuse in the supply line.
If both transmitters switch to transmit at the same time, the current required will exceed the capacity of the fuse and it will blow
so switching them off. A little while latter, it will reset itself and if the problem has cleared, then all is well and operation will continue as normal.
13...Although the cross-over cable is a standard part available from Team Simoco, it can also be made up by you if required. The
positioning of the two radios may actually dictate this as the cable comes in only one size. The maximum length you can make
them up in is about 3 metres but at this length, screened CAT5 cable should be used along with ferrite EMI filters where possible.
14...The terms ‘Rebroadcast’ and ‘Repeater’ are used almost interchangeably in this document. In fact a UKSAR ‘convention’ is becoming established where ‘Rebroadcast’ refers to the two-frequency-simplex system adopted by the Lake District and it’s near
neighbours. Whereas ‘Repeater’ is now more often used to refer to the wide area duplex system used by some teams. This latter
system is where the radios receive and transmit on different frequencies and normal simplex (back-to-back) operation is not possible. Strictly then, our system as used in the examples in this document, should be called ‘Rebroadcast’.
15...The Simoco radio model immediately before the SRM9000 series was the PRM8010/20 series. A number of teams still have
these radios and they are still good, workhorse sets. It’s possible using a small external circuit, to set up repeaters using these
radios. If anyone wants details, contact Rob Brookes (details at the back) and I’ll send them to you.
16...Due to the fact that the architecture of the SRM9000 vehicle radios is very similar to that of the SRP9100 handsets, I asked
TMC if it would be possible to make repeaters using these handsets. The answer is basically, ‘Yes’, but the handsets are not intended for this use where the vehicle sets are. As such a couple of small differences exist that, in theory, could be overcome externally so making this possible. I will take this one up with TMC and see if we can get some practical instruction as to how this
might be done.
17… If you are setting up two SRM9000 radios for use as a rebroadcast system even if one of them is also going to do service as
your vehicle’s main comms radio, the ‘Mute Speaker During FFSK’ option must NOT be checked. Doing so will prevent the data
getting through the system altogether. It will also, fairly obviously, result in the received data being heard in all it’s glory by the
vehicle radio. That, for the time being, is something we have to live with I’m afraid.
Programming Interface
for the PRM80 and
SRM9000 series
For those who want to wire up
their own
Programming lead for the Simoco SRP8000 and SRP9000 series hand portable radios
Contacts :-
Component suppliers and information
General information regarding this document:‘Simple’ and modified ‘Standard’ repeaters.
PRM80 repeaters (See ‘Notes’)
Remote channel-changing fixed repeater
Rob Brookes
LDSAMRA Comms Projects Officer
01539 728684
Team Simoco Ltd:Andy Gamble
Business Development Manager
Mobile: 07710 738171
DDI: 01332 375591
Fax: 01332 375501
‘Simple’ repeater
Stewart Devlin
Coniston MRT
telephone 015394-37273
TMC Radio Pty
CPC Preston:
‘Simple’ and ‘Standard’ Repeaters
Portable use of the ‘Simple’ repeater
Iain Nicholson
Bowland Pennine MRT
Enhanced software and selcall control of all repeaters
Dave Binks
Duddon & Furness MRT
Panorama Antennas
Operation using aerial separation rather than diplexers
Selcall control of ‘Standard’ repeater
Modified ‘Standard’ Repeater
Alan Prescott
Keswick MRT
ATDI Radio Propagation Plots
Roger Taylor, Tower Communications
Customisation of the Diplexers.
01353 749859
Operational use of the repeaters in the Borders
James Coles
Moffatt MRT
01387 251 083
MRMap -
MRMap-GPS-Tracking-Communications-Safety-Mountain Rescue-Mapping-Downloads-Free Software
Silent GPS Data Reception on a Simplex Voice Channel
Silent GPS Data Reception on a Simplex
Voice Channel.
A Guide for Team Communications and Training Officers.
MRMap Development Team 10/01/2009
Normally associated with power and loudspeaker connections, the 15 pin D connector
can also provide audio in and out plus two programmable pins, one, an input and the
other an output. These can be programmed to go either logic high or low when certain
conditions arise. They can also provide a cross-connected PTT arrangement where one
radio receiving a signal forces the other to go to transmit and with cross-connected
audio lines, anything received on one radio is re-transmitted via the second.
The circuit on the following page shows how this can be achieved.
This group of 4 connections
are used to provide the facility
connector rebroadcast
The pin 3, ignition sense contact used to
ensure the radio switches on when there
is no control head and therefore no other
indication of this having happened.
MRMap Development Team 10/01/2009
An Alternative Approach To Rebroadcast That Doesn’t Use The Standard
Cross-Over Cable.
Rebro Channel Radio
Pin 3 to Pin 4
Ignition Sense
Pin 3 to Pin 4
Ignition Sense
The connections between Pins 14 and 15 on both If required, a control head can be fitted to the TWC
D-15 connectors should be made using screened radio via the RJ45 port. If the power supply to the
cable. The screen is connected to pin 10
rebro channel radio is switched, then the system only
enters repeater mode if this switch is on. If not then
The ignition sense connection between pins 3
the primary radio functions as normal.
and 4 is sometimes necessary to ensure that the
radio switches on when power is applied. When
If both a control head and forward control GPS
used in a repeater or rebroadcast configuration
tracking of team members is required then an MAthere is no control head which would otherwise
ASIG accessory board configured for dual control
indicate this.
heads should or a standard Dmap board be fitted. The
control head is plugged into the accessory board and
No connections are required to the radio RJ45
the tracking computer is connected via the radio RJ45
ports and the red, cross over cable is not used in port.
this configuration. If required, GPS tracking at the
Repeater vehicle is handled by plugging the
Anyone looking for a short length of something
computer into the RJ45 connector on the TWC
suitable to make up the crossover cable? Have a look
to see if you have an old PC mouse lying about. The
cables on these usually contain four cores and a
screened foil sheath having a drain wire fitted that can
take a solder connection.
MRMap Development Team 10/01/2009
The image on the left shows the whole
rebroadcast setup with the lid off. The
radios are standard SRM9005s but are
fitted into a TSF2000, 1U, case and not in
their normal individual aluminium boxes.
The necessary heatsink is on the bottom
of each radio. The RJ45 port on the lefthand (TWC) radio is connected to
MRMap running on my Eee PC and the
device to the left of the computer, is the
The image below is a close-up of the
power/facility connectors. The heavier
black lead between the two
D-connectors carries the cross-over
connections that duplicate the job
normally handled by the red, RJ45
crossover lead. Both radio RJ45
connectors are available for use with
either a computer or a control head.
MRMap Development Team 10/01/2009
Programming the Radios.
The Portable Handset:
Although it’s assumed that a Simoco SRP9100 is going to be used along with a GPS microphone, the principles described here will work with any make of radio capable of using CTCSS.
This would add the benefit of no FFSK noise from Simoco-based GPS to users of other makes.
Just program the necessary channels in your radio with the tone 218.1Hz on both Tx and Rx. In
the case of Simoco radios it’s also a good idea to program one of the function buttons for CTCSS
disable in case you need to knock off the tone mute.
Note:- It’s important to realise that when using a fixed remote or vehicle mounted rebroadcast device set up
as described here that full Rx & Tx CTCSS then becomes an unalterable part of the system as it’s not
easily possible to switch the CTCSS on and off remotely. If the ‘CTCSS/DCS’ button is pressed on a
portable or base radio to prevent a CTCSS tone being used on either Rx or Tx then you won’t now be able
to access the rebroadcast device hence this is a committed method of operation. If used, then it’s really the
only method of operation you can use with your own area’s radio hardware.
Here the radio is programmed with a single instance of channel 53a. Note that CTCSS is programmed into
both the receive and transmit frequencies and that in my case, I’ve already changed to 12.5KHz channel
spacing. It makes no difference to operation if you’re still using 25KHz.
Next you need to make a slight change to the way in which the GPS functions are programmed. Most of
you will already have this section programmed correctly. Users of other makes of radio can ignore the following programming section.
MRMap Development Team 10/01/2009
This is my own radio so as you would expect, the MRMap data addresses are for my own
callsign. Here you would substitute your own information and the correct values for your team.
‘FFSK Data Rate’ is always 1200 baud.
‘ Que on Carrier’ means the radio won’t
send data if the channel is in use (and is
very important!)
As per previously published information, ‘FFSK ANI’
means you will send your callsign (Own Data Address) when you release the PTT and ‘GPS Reporting’ means the GPS position report will be tagged
onto this if you have a GPS mic fitted.
‘Mute speaker during FFSK’ does exactly that and
largely removes the data noise from the radio
‘Immediate Message Display’ is nothing to do with
silent GPS but means text messages are displayed
immediately rather than stored with the little
envelope symbol being shown.
‘Time Interval’ is the new GPS beacon function for
those wishing to use it and here my radio is set to
automatically send it’s position every five minutes
regardless of whatever else happens.
MRMap Development Team 10/01/2009
‘FFSK Lead-in delay’ is the amount of
time in milliseconds that must elapse
after you release the PTT before the
GPS position report is sent. This time
must be greater than the estimated
200ms of hang time for the CTCSS
mute gate of the receiving radio. This
means that the FFSK data is sent after
the mute has closed on the receiving
radio and is therefore not heard in the
‘Data CTCSS’ must say ‘Undefined’
and not ‘Unchanged’
‘Use LID for FFSK ANI’ means that the
lead-in delay will be used after the PTT
is released and was a requested function added by TMC. If you use an older
version of the FPP, then this and other
functions may not be available.
The Base Radio
Programming the base is essentially the same as for the portable radios. The Data Addresses are changed to reflect the fact that this is a base and no GPS data is being sent so no
FFSK ANI or GPS Reporting is necessary. Polling of the portables is handled by MRMap not directly by the radio itself.
Frequency information remains the same for both radios along with the CTCSS programming
When programmed as shown so
far, voice transmission will be as
it normally is but GPS data will be
completely silent. This also extends to text messages or any
other type of FFSK data sent by
either base or the portables.
MRMap Development Team 10/01/2009
Programming the Rebroadcast Radios.
This is where all the work was involved and where all the mistakes were made. A portable
radio working directly back to a base radio where both use full CTCSS has always resulted in silent GPS data. Getting it to work through the rebroadcast device needed a lot more work.
Set the Radio Type to 9005
External Serial
The majority of problems are caused by the fact that when the red cross-over cable (it doesn’t
have a proper name) is used then the CTCSS tone programmed into the individual voice channels is not used on transmit The only way for the rebroadcast to send a tone is for it to be programmed into the ‘Data CTCSS’ option. This results in the FFSK data again being heard by the
receiving radio as it now carries the correct tone to open to mute gate. Not what we want to happen.
Note:- You would think Press to talk, PTT, is just press to talk but not in these radios it’s not. So far I count
six different ways in which the radio either handles PTT or can be programmed to handle it. None are the
same as each other and all have differences in operation that make them unique to a specific type of usage. The PTT button on the microphone itself is not quite the same as ‘PTT Mic’ as can be programmed
into the rear D-15 connector and when using the RJ45 crossover cable which plugs into the same socket
that the control head does, PTT now automatically becomes ‘PTT Data’ which, again, is not the same as
just clicking the microphone PTT. ‘PTT Ext Data’ which once again can be programmed on the D-15 connector pins is different again and testing every programming combination against every possible PTT
method is what takes up the time on jobs like this. In the end, ‘PTT Ext Data’ is the one needed for this
task but it was the one I wasn’t even going to bother with as it didn’t sound like what I wanted. Turned out I
was wrong yet again!
MRMap Development Team 10/01/2009
Of critical importance are the ‘Data Volume’ which must be set at 15 and the selection of
‘Telemetry Output’
‘Data Volume’ sets the audio signal level on pin 15 of the rear facility (power) connector and is
the volume of the signal sent to the transmitting radio. A level of 15 causes no distortion of the
FFSK data whereas larger values can and lower values just reduce the audio volume.
Setting ‘Telemetry Output’ results in flat audio being used by the rebroadcast radios. That is no
pre-emphasis or de-emphasis or other audio processing is applied to the received or transmitted
signals. This runs the least risk of distorting the FFSK as it passes through the rebroadcast radios. Note however that setting this value causes the speakers to be disconnected from the radios and no audio is heard if they are left plugged in. This is as you would expect from a standalone rebroadcast but seriously messes things up if you use the TWC radio for normal comms as
you can’t now hear anything from it. This system is probably best used by teams who have fixedsite rebroadcast setups and teams who use the three-radio configuration in their vehicles. Two for
rebroadcast and the third to handle the normal vehicle comms. .
MRMap Development Team 10/01/2009
Next to be programmed is the Input/Output values which are shown below.
Don’t be tempted to use ‘Valid Signal’ instead of ‘Carrier Detect’ as this means the data, which
doesn’t have a CTCSS tone attached, won’t enter the rebroadcast unit so only the voice signal is
Likewise ‘PTT Ext Data’ must be used rather than ‘PTT Ext’.
A ‘Data Volume’ of 15 as recommended earlier results in good but not ‘punchy’ audio. If you are
using the programming software set at Level 3 then you will also have access to the audio level
controls. None of these other than the ‘Compression Gain’ need to be changed but bringing this
up from 0 to 6 or even 12 will increase the level of transmitted audio without risk of distortion to
the GPS data.
MRMap Development Team 10/01/2009
Programming of the TWC side of the rebroadcast unit is the same for the 147.35MHz radio but for
the actual frequency used. The need to use a diplexer with an in-band rebroadcast device means
that it’s not really much use in programming any other frequencies in but this has the advantage
of there being no danger of popping up on the wrong channel as there’s no control head to tell
you you’ve done this.
On the ‘Channel <> Options’ page the most
important setting is the ‘Repeater Tail’. This is
the amount of time that the repeater remains in
transmit mode after the station calling in has
released it’s PTT. Although this is 600ms, just
over half a minute, this is a life-time in the normal course of events for these radios. Even
shifting the time by 50 milliseconds has a profound effect and 600ms was the time found to
work most reliable. In fact 100% reliably in
tests. It might be possible to shorted it however.
I’ve used ‘Reverse Tone Burst’ as this removes the squelch tail, the shhhssssss on the
end of each transmission as the various mute
gates close. This results in a received signal
that is much cleaner and does far less ear
bashing than it usually does.
I run at 1 watt RF power when testing which is
why the power levels look a bit strange.
MRMap Development Team 10/01/2009
This is the page on which, again, a number of mistakes were made in earlier attempts at this. The
radios are programmed as a base using the values shown in the ‘Data Addresses’ box. These
are also the factory default values that will be found in a new radio. With these values, the TWC
radio can also act as a GPS base radio if connected to a laptop running MRMap. However, as it
doesn’t have a unique callsign, it can’t be used to send position reports back to base.
No values are set in the ‘Options’ box but especially the ‘Mute speaker during FFSK’ should
never be set in a rebroadcast or repeater unit as this prevents FFSK from being passed through
the device. With the ‘FFSK’ values, a discussion with the engineers at Simoco Huntingdon
resolved some logical issues that had been causing difficulties. Again the FFSK Data Rate
remains at 1200 baud.
In the case of rebroadcasters or repeaters, there’s no advantage in getting them to hold off if the
channel is in use as chances are, any other signals will be going through the device anyway.
There’s no need to set a lead-in delay for FFSK in a repeater or rebroadcaster as they aren’t
being required to generate any FFSK data themselves, only to pass through any data that they
receive. Because of this there’s no need for the ‘Use LID for FFSK ANI’.
Again, ‘Data CTCSS’ must be set at ‘Undefined’ which means no CTCSS tone is sent when the
data is transmitted. This is the critical config value that makes it all work.
MRMap Development Team 10/01/2009
The system described here has been run at full power around the Kendal area. I have an antenna
at both ends of the house roof for testing things like this and the 147MHz link was only transmitting down the length of the house. However the TWC radio was required to operate to a moving
vehicle several miles away and no polls or replies were missed. All the types of polling of GPS
equipped radios was tried and several handsets were operated alongside the rebroadcast unit.
Not all of these were SRP9100s or indeed, Simoco radios and in none of them was the FFSK
data audible when CTCSS was enabled on receive and transmit.
All received data, be that at the ‘base’ end or in the vehicle itself, was completely silent but voice
transmissions were received normally although the usual squelch tail was thankfully absent.
The amount of wiring needed in the power/facility connectors is not great and is easily done by
anyone who can wield a soldering iron. This can be taken a stage further if required as LED operation indicators can be wired to the same pin 8 and ground.
Still to do:
Firstly I need to check that the same system also works with a cross band rebroadcast unit.
Next, will it work with an SRM-based, duplex repeater as against a rebroadcaster?
Hopefully finally, I need to re-introduce the ability to change channel in the cross band rebroadcast. This is lost due to the absence of the red crossover lead in this system. However, TMC in
Australia advise me that the rear, facility connector PTT lines take precedence over the RJ45
crossover cable. The audio connections on the RJ45 X-over cable are not required and can be
left out as can all the other connections on this cable except those on pins 1 and 2. These two are
the data connections that handle the remote channel changing instructions in a cross-band rebroadcast.
Unfortunately they are also the connections that handle PTT when this cable is used to facilitate
rebroadcast or repeater operation, however, TMC did say that the rear facility connector takes
PTT precedence. So far I don’t know whether this is correct but as soon as I’ve wired up a quick
two-wire cable (!) I’ll give it a go. (Done)
One last thing, even though the FFSK speaker mute on Simoco radios does satisfactorily remove
90% of the data noise, it’s still very weird to see the plot move or watch ‘GPS Poll’ come up on
the radio display but to hear absolutely, and that really is absolutely, nothing. For ten years now
I’ve been listening to radios beep away at me and now it’s gone, I quite miss it.
MRMap Development Team 10/01/2009
Remote Channel Changing in cross-band rebroadcast systems:
The basic rebroadcast functions are now provided by the crossover connections fitted to the rear
power/facility plug. The standard Simoco crossover lead is not required for plain, single channel
rebroadcast. However if you have a system on which you need to be able to change the operating
channel via your link radio, then the addition of the cable described here will enable that for you.
Only two connections are actually required in the cable but a short test would seem to indicate
that the original, unmodified cable can also be used. Whether this will have any effects on the
transmitted audio is not known. It doesn’t appear to over the short distances of the test.
Leaving this cable out doesn’t affect the basic rebroadcast function and leaving it in if you’re not
using channel changing likewise has no detrimental effect. For basic rebroadcast however, it’s
not necessary.
Operation Indicator Lights:
As pin 8 on the power connector is programmed to go
low, when a signal is received, as part of the normal
operation of the rebroadcast, If you wish, you can add
an indicator light or LED which gives visible indication
that each radio making up the rebro is actually working.
As this configuration doesn’t need or have a control
head fitted, there’s not really any other way of getting
this indication. Fitting an LED here has no effect on
the operation of the Tx/Rx side of things. Some form of
operating indication is to be recommended as when
using the Telemetry Output option, the loudspeakers
are cut off and there’s nothing to hear when either
radio receives.
MRMap Development Team 10/01/2009
What to watch out for and what didn’t work:When programming a rebroadcaster for remote channel changing, the ‘Remote Options’
checkbox needs to be checked as shown below.
Radio Type - SRM9030 Secall options page
However, if you’ve already set the Radio Type on the first page to, ‘9005 External Serial’ as recommended then a number of programming options disappear. With no control head, there is no
need to be able to program functions into the keyboard or microphone keys. ‘The Remote Options’ check box is also hidden. The only way around this is to select a radio type that uses a
control head initially, SRM9030 for example. Check the Remote Options box and then change
the Radio Type back to ‘9005 External Serial’. The Remote Channel Change check box is still
active even though you can no longer see it.
Radio Type - SRM9005 External Serial. Same page
MRMap Development Team 10/01/2009
One where I’ve so far failed miserably is putting a single selcall tone onto the end of the transmission made by the rebroadcast radios so as to act as an indication that you are still within range of
base. This is sometimes called a ‘Comfort Tone’. I couldn’t get a tone at all from either of the
rebro radios using ‘PTT Data Ext’. It would seem from trying all the others that only the actual
microphone PTT button can initiate the sending of the ‘PTT Off’ selcall tone.
As a way around this I tried adding the tone to the end of the base transmission as it’s passed
straight through the rebro and, sure enough, if the microphone PTT was pressed then a tone was
sent. However under these circumstances you would already know that you were still within range
of base as you would then hear them speak. What’s needed is a tone at the end of the otherwise
silent, automatic group poll sent out by MRMap. This I couldn’t achieve but I’ll keep on trying until
I’m sure it can or can’t be done. I did get some odd delay effects under certain circumstances but
not an actual tone so it may be some setting I have wrong (again!) Unfortunately, doing it this
way adds yet more time to the operation cycle of the rebro and there is already a short but noticeable period after a handset transmits, when it can’t open the rebro receiver for a second or two. I
also need to look at this. If anyone wants to help with the selcall tone testing, please feel free!
Still left To Do:Just whether it will work with a duplex wide area repeater really. The rest is just tidying up
and refining the timing values. As so far described it will work and will probably be suitable for
those who just want to mute out the FFSK data noise. As and if I refine any of the config values,
I’ll update this document on the blog page and on the documents download page of the MRMap
MRMap Development Team 10/01/2009