Forward Sweep and Balance

Forward Sweep and Balance
Application Note
Using JDSU‘s Family of SDA Sweep for Forward and Balance
Step-by-Step Headend Set-up
Set-up of forward sweep (see diagram below)
A diplex filter is used to combine reverse signals into the rack mount unit instead of a splitter or DC-12 because of isolation issues, and the return fiber receiver is more than likely 5-200 MHz. This could cause jitter on the forward sweep if not
set-up properly. Because the Stealth transmitter must see itself, be careful with what is in this “loop”, such as launch amps,
filters, etc; it could cause problems.
Note: Be sure input levels are between 4 and 12 dBmV. The recommended is 6 dBmV ± 2. If levels are too high, channels
may be enabled that aren’t even there. Levels too low will leave channels disabled that otherwise should be there.
The Stealth Headend Transmitter (Tx) and Multiple User Reverse Receiver (Rx) recommended input for reverse RF is
0 dBmV ± 2. It may work between ± 10 dBmV, but it depends on the aggregate noise floor.
WEBSITE: www.jdsu.com
Application Note: Using the SDA Forward Sweep and Balance
Build channel plan (configure; channel plan)
The Tip Box
It’s faster to build a
channel plan using
StealthWare. Version 6 is
the latest.
The Tip Box
When making labels, the
up and down diamond
keys can be used to
access special symbols
(i.e., “@”, “$”, etc.).
To get to a certain
channel quicker than
scrolling, go to the
“Level” mode, type in the
channel number, than
go back to “Edit Channel
Plan” or press func. 4.
If a channel plan has already been made, choose it from the
list under “Select Channel Plan”.
Note: The newest Stealth field meter replaced many of
the menus with icons. The “Set-up” button has been
replaced with a “Configure” mode, which can be
accessed through the “Navigator” mode, or by pressing “func” (green key) and the number 3 key. Channel
plans and files names are limited to 15 characters.
1.
“Video Signal Type”
NTSC for North America, PAL or SECAM for Europe
2.
“Build Channel Plan”
The forward channel plan should be set-up on the Tx
or StealthWare.
a. “Enter Plan Name”
b. “Type of Plan” (NCTA is common in North America,
but could be HRC or IRC)
c. “Stop Frequency” (be sure to press “enter” then “ok”)
3.
“Edit Channel Parameters”
• Enable or disable channels appropriately
• Enter tilt channels, sweep channels and/or scrambled channels
• Enter the type of channel
(Single, TV, Dual, Digital, QAM Digital Stream, Sweep
Insertion Point)
Note: “TV” is for regular, analog television signals; “Single”
designation is used for continuous wave (CW)
carriers; “Dual” is for NICAM not Secondary Audio
Programming (SAP); “QAM Digital Stream” is for 64
or 256-QAM carrier designation for the new QAM
option; and “Digital” is for regular digital ‘haystacks’,
regardless of modualtion type. Do not delete unused
channels until sweep points are made. If all disabled
channels are deleted, there will be no sweep points
made.
Build sweep points (configure; channel plan;
build sweep points)
This is an option on the Tx only. Sweep insertion points are
for vacant bandwidth and channels which are disabled to
allow sweeping of the entire spectrum. The default is ch. 2 to
1 GHz for the sweep, but sweep points can be inserted anywhere between 5 MHz and 1 GHz. Sweep insertion points
are not automatically inserted in the FM band. You must do
this manually if required.
Build insertion points for disabled channels; 2 is the default,
3 is the max, 1 is sufficient in most cases. Sweep points are
approximately 2.8 ms in duration and approximately 100
kHz wide.
2
Note: Ensure that no sweep insertion points are built within
6 MHz of either side of the ALC frequency. This could
cause problems with the ALC circuitry in certain
amplifiers.
Sweep transmitter (configure; sweep
transmitter)
“Sweep Mode” must be in the appropriate mode to allow
proper operation. The “transmit” mode is the older Stealth
Sweep, whereas the new “transmit (SDA compatible)”
mode is for the faster sweep refresh with digital and scrambled carriers present. The wrong mode selection will create
erroneous readings.
“Forward Telemetry Frequency” must be in the vacant spectrum and at least 500 kHz from any other carrier; it must
also be within the bandwidth of the downstream spectrum.
This is an FSK carrier and approximately 500 kHz wide. The
factory default is 51 MHz on the Tx, 52 MHz on the Rx, and
53 MHz on the PathTrak HSM.
Note: If diplex filters in the actives have a sharp roll-off, it
may be wise to move the telemetry to a frequency
that is more reliable. The location and level of the
telemetry can cause its second harmonic to interfere
with existing channels if not taken into account.
“Forward Telemetry Level” determines the level of the
telemetry signal. This should be set 10 dB below the video
reference level. The telemetry level is adjustable from 20-50
dBmV in 2 dB increments. The max is 50 dBmV, however
some older units may have a max of only 40 dBmV.
“Forward Sweep Insertion Level” is the level at which sweep
insertion points will be inserted; 40 or 50 dBmV is the max.
Sweep points should be 14-16 dB below the video reference
level. Sweep points fall on the video and/or audio frequency
of unused channels by default, but can be moved.
Note: Initially, set the Telemetry and Sweep Insertion levels
to the minimum of 20 dBmV each. Change the sweep
insertion level until the sweep insertion points are 1416 dB below the closest visual carrier.
This can be seden on the diplay when the sweep is
activated. Once the sweep is set correctly, change
the Telemetry level to 4 dB above the Sweep Insertion
level.
“Include Audio Carriers” means that the sweep display will
include all audio carriers; if you chose no, the sweep will be
faster but will display less resolution.
“Enable Reverse Sweep” allows reverse sweep to operate. If
disabled, the forward sweep will be faster.
“Enable Live Headend Ingress View” allows reverse noise
to be transmitted on the forward telemetry. If disabled, the
forward sweep will be faster.
Application Note: Using the SDA Forward Sweep and Balance
The Tip Box
The “Tilt” mode is simple and makes selecting
EQs very easy.
The Tip Box
The “Tilt Compensation” mode of the field
unit makes it easy to get
a true peak-to-valley no
matter what the tilt of the
reference.
The highest tilt channel
programmed in your
channel plan is the most
affected point, and the
lower tilt channel would
be the pivot point. If no
tilt channels have been
enabled, tilt compensation won’t work.
“Reverse Telemetry Frequency” is not applicable for forward sweeping.
“Reverse Sweep Plans” is not applicable for forward sweeping.
Copying channel plans
Ensure the sweep receiver is connected to the Tx by means
of the 9 pin, RS-232 connector on the back of the receiver
and the front of the Tx. This cable is supplied by JDSU and
has a specific pin configure (refer to manual for cable pin
configuration). Also be sure that the baud is identical on
both pieces of equipment.
Note: The headend unit’s channel plan does not have to be
downloaded to the field unit to achieve sweep. Only
the telemetry has to be the same. The channel plan in
the field unit doesn’t affect the sweep, only the other
measurement modes like “level”, “tilt”, “scan”, etc.
Note: If a channel plan is made on an older field meter and
copied to the Tx, the Tx will freeze up and must be
shut off to reset. One way around this is to transfer the
channel plan to Stealthware then from a computer to
the Tx. You can copy channel plans from field unit to
field unit or from the Tx to a field unit.
On the receiver, select (Configure; Channel Plan; Copy
Remote Plan) and enter the forward plan for the system you
are working on. The Tx then downloads the plan you have
built, but “sweep points” don’t show up in the hand-held
channel plan unless it has the portable transmitter option
installed.
Field unit settings
Select (Configure; Measurement) and insert all the required
information (Temperature Units, Signal Level Units, Fundamental Hum Frequency, Scan Rate, etc.).
Note: Select “func” and “7” to enter the Test Point compensation. You can also access the Test Point
compensation through the Navigator screen on the
newest unit. There is a toggle button to select forward
or reverse Test Point compensation.
On the receiver, select (Configure; Sweep Receiver) and set
the forward sweep telemetry frequency to be the same as the
Tx. Set for the sweep mode intended to be used. Depending
on the options installed in the field unit, these modes are as
follows:
“Sweepless”, “Stealth”, “SDA Compatible”, “Loopback
Sweep”, “Transmit”, and “Transmit (SDA compatible)”. Normally we would select “Stealth” or “SDA Compatible”.
3
Before you leave the headend
Be sure the Tx is in the sweep mode.
When at the headend, ensure that your forward tilt channels are working correctly by pressing the “Tilt” key. Then
check the sweep. The sweep direction can be changed on the
receiver by using the left and right diamond keys or selecting the following sequence: (Configure; Sweep Receiver;
Sweep Direction).
A forward sweep reference can also be taken at this time.
Press “func” and “6” and enter a name for your reference.
Some systems may want to use this reference for tap output
responses.
Note: Be careful with forward fiber optic transmitters in the
headend. The test point may be aligned for the input
to the “box” or the actual input to the laser diode. This
could give a faulty reference.
Forward balancing and sweeping
First, balance the signal levels at the node using your “Tilt”
and “Level” modes at the bandedge frequencies. Press
“Sweep” and verify all is well. Press the right diamond key
for forward sweeping.
Build your reference using the same procedures you used to
build the reference at the headend. Store a reference for each
leg of the node that has actives attached.
Note: It’s good to compare “apples” to “apples”. Don’t
change things like in-line pads and test leads once a
reference has been stored. Store a new reference otherwise.
Proceed to the next active in line. Use a directional test point
on the active for forward balancing and sweeping. Most forward balancing is based on unity gain at the output. If the
design slope is different than the node design slope, use tilt
compensation.
Note: The “max/min” displays the peak-to-valley between
the markers. The delta displays the difference in level
and frequency at the markers.
In forward sweep, the field unit has a max input of
approximately 20 dBmV/ch for a fully loaded system. This is usually not a problem on the high loss
test points, but could be an issue when connecting
directly to a seizure screw.
The default option is to dwell on all carriers (Stealth
unit must have digital option installed to monitor
digital levels), which could slow down the sweep
update time depending on the total number of digital
and scrambled channels. The newest unit with the
SDA Compatible mode utilizes a different algorithm
to speed this up by 5 times.
Application Note: Using the SDA Forward Sweep and Balance
Common forward sweep problems
Standing waves
• Use a directional test point if available. Standing waves
could still occur if a mismatch is severe and close
enough.
• Read from a tap. Some lower value taps may still give
reflections depending on port-to-port isolation and
portto- output isolation.
• Use a plug-in test point not a probe. Probes will always
be bi-directional unless they are in series with the
circuit and a directional coupler is used.
• Install a terminating tap (4 port 8 or 8 port 11) if you
have the luxury (make sure you terminate the spigots).
It’s an easy way to isolate the system.
• Verify for good test leads, connectors, F-81 barrels, etc.
• Use an in-line pad on your test lead to see if the standing wave goes away. If so, there is a reflection being
created between the field unit and test point.
Spikes
• Keep the resolution to approximately 6 MHz for forward sweep. This lowers the probability of inadvertent,
overlapping sweep points and transients. A sweep
point every 6 MHz is sufficient in most situations for
forward sweeping.
It also creates a faster sweep update and less memory
required for each stored trace.
• Verify proper set-up, levels, channel types, no overlapping sweep and actual channels, etc.
• Avoid common problem areas such as strong off-air
broadcasts (analog and digital) and certain FM channels.
No communication
• Verify the appropriate telemetry; keep it high and
located in the passband. Watch out for sharp diplex
filter roll-off and old 550 MHz passives in a 750 MHz
system. The minimum level for telemetry is approximately -15 dBmV and the max is approximately +12
dBmV. We sometimes lose communication on input
test points because of the lack of gain from the active
and the test point loss. Use the spectrum mode with
“max hold” on to verify the existence of the telemetry
and the level. Make sure test point compensation is 0.
• Verify test equipment connections, amplifier continuity, active gain, and that no terminators are installed.
Just use the “level” mode to see if actual channels are
present. If so, then there must be continuity.
• Verify the instrument is sweeping in the correct direction. Press the right diamond key and look in the
upper right corner of the field unit display.
• Press “Sweep” on the Tx. (Sometimes it’s the little
things that kill.)
4
Bad response
• Verify accessories are operating correctly such as cable,
push-ons, older summation networks (DDC-20),
pads, etc.
• Low sweep points may get confused with the noise
floor, especially after going through more actives with
their associated noise figures. This could cause the
“grassy” effect on the sweep display. Increase the sweep
insertion level on the Tx to verify.
• Use the correct sweep mode. The wrong mode could
lead to problems.
• If input levels are too high, this could cause extreme
intermodulation distortions, which could affect the
associated sweep points.
• Firmware versions must be the same on the transmitters and receivers. Older Stealth units with firmware
versions 8.5 and 9.3 are not compatible and will yield
inaccurate sweep measurement results. Version 9.3
will work with the new SDA units, but not in the SDA
Compatible mode.
Faster forward sweep
Note: These are only suggestions and discretion must be
used.
• Disable the Reverse Sweep and Live Headend Ingress
View if present (Configure; Sweep Transmitter.)
• Don’t sweep the video frequency of a scrambled channel. Leave it enabled, but don’t use it as a sweep point.
Insert another channel at the audio frequency, change
the type to “single channel” instead of “scramble”,
and use it as a sweep point. This assumes the audio is
stable.
• Disable all audio readings; only use single insertion
points (Configure; Sweep Transmitter.)
• Place sweep points in the lower sideband of analog
channels, especially sync suppressed scrambled channels, and in the guardband of digital channels. 1 or
1.1 MHz below the analog channels seems to be the
“sweet spot”. Dwell times are set at 4 ms for a standard
channel, 2.8 ms for a sweep point, and 158 ms for a
scrambled or digital channel.
Note: This new plan doesn’t have to be loaded or enabled in
the field unit for sweep to be achieved.
• Use the new SDA Compatible mode to speed up the
dwell time on digital and scrambled channels and still
remain non-intrusive.
Application Note: Using the SDA Forward Sweep and Balance
Frequency response identification
• Low End Roll-Off or Instability
° Usually caused by loose seizure screws, bad EQs/CSs,
diplex filters, or dirty fiber connections.
• Standing Waves
° Created from reflections from impedance mismatches. This is seen when viewing a sweep display
from a resistive/bi-directional test point. Directional
test points have enough isolation to block the reflected
wave (depending on the severity) from adding in and
out of phase with the main wave, which creates the
standing wave appearance. They can even be created
between the test point and test equipment. If you use
the formula 492*Vp/f, it will tell you the “ballpark”
distance in feet to the fault. Vp is the velocity of propagation of the cable and is typically .87 for most foam
dielectric, hard-line cable. Using this formula, “f” is the
separation in MHz between two peaks on the sweep
display; 492 is derived by the speed of light, which is
984 Mft/s and the fact that the reflection is 180 degrees
out of phase for 984/2 = 492. This also could be a
reflection between the test point and test equipment,
especially on 20 dB testpoints.
• Suck-Outs
° Caused by grounding issues or multiple impedance
mismatches at perfect intervals. Sometime this also
manifests itself as spikes because of signals adding
in-phase. Spikes are also caused by oscillations and
ingress.
• High End Roll-Off
° Associated with bad accessories, water, cracked
sheath, or amplifier bandedge roll-off.
Other applications
Using the portable receiver transmitter for
forward activation.
JDSU’s portable Stealth Sweep transmitter and receiver can
be utilized to perform the following:
• Balancing inactive plant; One could insert the receiver
transmitter into the node where the optical receiver
usually inserts. Store a reference at the Node output.
Proceed to the next active in cascade and balance back
to the same reference line and telemetry level, which
was achieved at the node. This is assuming that the
next amplifier will be running the same tilt and output
levels as the node. Otherwise, offset accordingly.
• Single amp bench alignment; When in the Loopback
Sweep mode, the portable sweep transmitter/receiver
reads its own signals. One could use it to see the frequency response and gain of a single amplifier. Set-up
a channel plan with sweep points every 2 MHz for
good resolution. The total number of points is limited
to around 500. Be sure to store a reference of your test
leads before sweeping the device.
5
Tips & Hints
1. Because the Stealth default set-up uses the actual channels for sweep, and inserts sweep points where there
are no active carriers, there is no interference to the
TV picture.
2. The field unit is capable of a frequency agile, CW
carrier at 50 dBmV (40 dBmV for the older version).
Select (Configure; Diagnostics; Transmitter Diagnostics) and set the Tx frequency, attenuation, and turn
the Tx on.
Note: You must leave the field unit in this mode for the Tx to
stay active. The cable must be attached to the “OPT”
port on the field unit.
3. If headend channel levels change, a new reference will
NOT be required because the Tx will automatically
compensate. It can’t compensate for continuously
fluctuating levels though.
4. The sweep file overlay is a nice feature to view an existing stored file and see the actual sweep trace overlaid.
Select (Configure; Sweep Receiver, Sweep File Overlay) and turn it on. You can even upload an old file
from Stealthware into the field unit to do an overlay.
5. Select “Func” & “i” for instrument information such as
calibration date, serial number, options installed, etc.
6. The field unit is dc blocking to 200V peak-to-peak.
This equates to approximately 100 Vac.
7. Once a trace is stored, you can alter the dB/div, start &
stop freq., tilt compensation, etc. To print this altered
trace, hit “Func” & “Print”. (Use the printer serial cable
supplied by JDSU.)
8. The de-facto standard is 2 dB/div for sweeping and 5
or 10 dB/div for spectrum analyzer viewing.
9. The new SDA unit has added a CW Loopback mode
that is accessed through the Navigator screen. Consult
JDSU for a list of other new features.
10. You can change the start and stop frequencies in the
sweep mode of the field unit, which makes it easier to
move your markers around.
11. Type in the frequency and hit “enter” to make a marker jump to that frequency.
12. Use “Zoom” to zoom in between the markers.
13. If you don’t know the frequency of a certain channel,
use the level mode. Type in the channel number, hit
the “Channel” key, then hit the “Freq” key.
14. The Tx will transmit/broadcast the ingress from all
the return amplifiers connected to it back to the field
unit.
This will be transmitted on the forward telemetry
with 280 kHz of resolution. Return continuity is not
needed for this reception. The noise mode on the Rx
transmits the total noise in the headend also, but with
a resolution based off the return channel plan resolution.
6
Application Note: Using the SDA Forward Sweep and Balance
15. You can sweep without downloading the channel plan, but other measurement modes won’t operate correctly, such
as the “Tilt” mode. You must assure the same telemetry frequency.
16. The unit sweeps 4 times before a reference can be taken.
17. The number of sweep points is limited to 500, but inserting too many will make the refresh of the sweep display
slower and take up more memory for storage of files. The sweep update time is dependent on the set-up.
18. “Show Horizontal Markers” (Configure, Sweep Receiver) is a nice feature to view the maximum peak and lowest
valley between the vertical markers.
All statements, technical information and recommendations related to the products herein are based upon information believed to be reliable or accurate. However, the accuracy or completeness thereof is not guaranteed, and no
responsibility is assumed for any inaccuracies. The user assumes all risks and liability whatsoever in connection with
the use of a product or its applications. JDSU reserves the right to change at any time without notice the design,
specifications, function, fit or form of its products described herein, including withdrawal at any time of a product
offered for sale herein. JDSU makes no representations that the products herein are free from any intellectual property
claims of others. Please contact JDSU for more information. JDSU and the JDSU logo are trademarks of JDS Uniphase
Corporation. Other trademarks are the property of their respective holders.
© 2006 JDS Uniphase Corporation. All rights reserved. 30137255 500 0806 SDAFWDSWEP.AN.CAB.TM.AE
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