LDG AT-1000 Pro
1000-Watt Automatic
Memory Antenna Tuner
LDG Electronics
1445 Parran Road
St. Leonard MD 20685-2903 USA
Phone: 410-586-2177
Fax: 410-586-8475
[email protected]
Table Of Contents
Tuner Safety Warning
Important Antenna Safety Warning
Jumpstart, or “Real hams don’t read manuals!”
Getting to know your AT-1000 Pro
Front Panel
Rear Panel
Front Panel Button Description
Power / Func Button
Auto / Thresh Button
Ant1 / Scale Button
C Up / Peak Button
C Dn Button
L Up
L Dn Button
Tune/Store Button
Operation - Basic
A Word About Roll-Back Circuits
Fully Automatic Mode
Semi-Automatic Tuning: Request Memory Tune Cycle
Semi-Automatic Tuning: Request Full Tune Cycle
Operation - Fine Tuning
Manually Adjusting Tuning Parameters
Storing Manually Adjusted Tuning Parameters
Operation - LED Blink Codes
Application Hints
MARS/CAP Coverage
Icom Radio Interface
Optional Yaesu Radio Interface
Build-Your-Own Interface
Theory of Operation
Some basic ideas about impedance
Transmitters, transmission lines, antennas, and impedance
Returning Your Product For Service
Product Feedback
The LDG AT-1000 Pro
A Word About Tuning Etiquette
Care and Maintenance
Technical Support
Two-Year Transferrable Warranty
Out Of Warranty Service
LDG pioneered the automatic, wide-range switched-L tuner in 1995. From its laboratories in
St. Leonard, Maryland, LDG continues to define the state of the art in this field with innovative
automatic tuners and related products for every amateur need.
Congratulations on selecting the AT-1000 Pro 1000-watt automatic tuner. The AT-1000 Pro
provides semi-automatic and fully automatic antenna tuning across the entire HF spectrum plus 6
meters, at power levels up to 1000 watts (SSB). It will tune dipoles, verticals, Yagis, or virtually
any coax-fed antenna. It will match an amazing range of antennas and impedances, far greater
than some other tuners you may have considered, including the built-in tuners on many radios.
The AT-1000 Pro is an upgrade from LDG’s previous AT-1000 kilowatt tuner, in that it now
supports fully automatic tuning (Just talk and it tunes!) with frequency-based memories for high
power amplifier applications.
The AT-1000 Pro internally switches a very large amount of radio frequency energy.
Tremendous RF currents flow through the tuner, and sometimes very high RF voltages are
present during operation. The AT-1000 Pro is designed to handle this RF energy safely within its
specifications, with a reasonable margin of safety.
However, be warned that some amateur amplifiers are capable of transmitting RF energy in
excess of the AT-1000 Pro’s maximum specifications. Some are capable of levels far in excess
of these specified maximum levels.
Operation under conditions exceeding the maximum specified ratings of the AT-1000 Pro
will cause damage to or destroy the AT-1000 Pro. Operation in significant excess of the
maximum specified power levels can actually cause explosion of internal components. For this
reason, and because of the lethal RF voltages present during normal operation, never operate
the AT-1000 Pro with the cover removed.
Never install antennas or transmission lines over or near power lines. You can be
seriously injured or killed if any part of the antenna, support or transmission line touches
a power line. Always follow this antenna safety rule: the distance to the nearest power
line should be at least twice the length of the longest antenna, transmission line or
support dimension.
Ok, but at least read this one section before operating the AT-1000 Pro:
SAFETY WARNING: Never operate the AT-1000 Pro with the cover removed. Lethal RF
voltages are present during operation. Also, never exceed the rated specifications.
Turn off power to your radio and amplifier.
Connect the antenna jack on your amplifier to the “Transmitter” jack on the AT-1000 Pro,
using a 50 ohm coax cable jumper. Be sure that the coax jumper can handle the RF power level
from the amplifier. Connect a 50 ohm coax antenna feedline to the “ANT1” jack on the AT-1000
Connect the AT-1000 Pro to a source of 11 to 15 volts DC, 1A, using the supplied coaxial DC
power plug. Press the “Power” button on the front of the AT-1000 Pro to turn on the tuner. The
“Power” LED and meter backlight will come on.
Turn on power to your transceiver and amplifier and select the desired operating frequency and
mode. Place the amplifier in Standby mode so that it does not operate when transmitting.
Press the “Auto” button on the AT-1000 Pro to turn off fully-automatic mode. The Auto LED
will go off.
Transmit a carrier from the exciter of approximately 30 watts CW, FM, or AM.
While transmitting the carrier, momentarily press the “Tune” button on the AT-1000 Pro.
Continue transmitting the carrier until the tuning cycle stops.
Check the meter to see that the SWR is below 2:1 before using the amplifier.
Switch the amplifier to active mode; you are ready to transmit!
Continuous frequency coverage 1.8 to 54 MHz (Including MARS, CAP, etc).
Transmit Power Rating, 1.8 to 30 MHz:
Single Side Band: 1000 watts
CW: 750 Watts
Digital (RTTY/Packet/PSK31, etc): 500 Watts
Transmit Power Rating, 50-54 MHz: 250 watts, all modes.
Minimum power required for tuning: 5 Watts
Maximum power while tuning: 125W
Built-in relay protection will prevent relay operation when:
Greater than 200 watts input power under any load.
Greater than 150 watts input power when load is 3:1 SWR or greater.
Built-in two position antenna switch.
3” cross-needle illuminated Power/SWR meter with dual power scales, 0-100 and 0-1000
watts. Selectable Peak and Average power display.
2000 memories per antenna port for instantaneous band changing.
Microprocessor-controlled Switched L tuning network.
Fine tune controls for manually adjusting capacitance and inductance.
Time required for tuning: 200 ms for memory recall; 10 seconds average full tune; 30
seconds maximum full tune time.
Built-in frequency sensor allows instant recall of previously-tuned frequencies.
Tunes 6 to 1000 ohm loads (About 10:1 SWR), or 16 to 150 ohm loads on 6M (3:1 SWR)
For Dipoles, Verticals, Vees, Beams or any Coax Fed Antenna.
Includes 6 foot DC power cable.
Optional interface cables available.
Power Requirements: 11 to 15 VDC, 1.0A
Dimensions: 9.5”W x 13”L x 3.5”H.
Weight: 5.2 pounds
Your AT-1000 Pro is a quality, precision instrument that will give you many years of
outstanding service; take a few minutes to get to know it.
Front Panel
The front panel of the AT-1000 Pro sports eight pushbutton switches and a 3” illuminated
cross-needle meter.
The front panel pushbuttons are as follows:
Power: Turns the unit on/off. Also serves as the Function button.
ANT1: Toggle antenna selection.
Auto: Turn fully automatic tuning on/off.
C Up: Increase capacitance.
C Dn: Decrease capacitance.
L Up: Increase inductance.
L Dn: Decrease inductance.
Tune: Initiates memory or full tuning cycle. Momentary push toggles bypass.
The Power switch on the AT-1000 Pro toggles between the “Off” and “On” modes. Note that
even in “Off” mode, the AT-1000 is not completely “off”, but rather in a very low power sleep
mode. In “Off” mode, the AT-1000 relays are completely de-energized, placing the tuner in
bypass, selecting the ANT 2 antenna, and no LEDs are illuminated. When the Power button is
pressed, to turn the AT-1000 Pro “On”, the previous relay settings are restored, including
antenna selection. The Power button must be pressed and held for 3 seconds to turn the AT-1000
Pro “off.”
Each pushbutton contains an integrated LED that indicates the status of that button’s
function. Other tuner status may also be indicated on the LEDs; see the section “Operation LED Blink Codes” for more detail.
Most pushbuttons on the AT-1000 Pro also have a secondary function, which is activated
when the button is pushed while in Function (FUNC) mode. The button’s secondary function is
listed under the button. Function mode is entered by pushing and holding the Power button for 1
second, until all the panel LEDs light up, and then releasing.
The illuminated cross-needle meter indicates forward and reflected power, as well as SWR,
all at once. Forward power is indicated in two ranges; 0-100W and 0-1000W. If the 1000W
range is selected, multiply the indicated power by 10 to give the actual power.
Readings are accurate to ±10% across the full scale. Forward power is indicated in “Peak
Hold” mode or average power mode. In Peak Hold mode, the peak power is indicated, then held
for a moment before dropping to a lower indicated level. Power indicated is the true peak
reading. Average power mode displays instantaneous average power.
The cross-needle meter displays SWR as the intersection of the Forward and Reflected power
indications. For example, in the photograph at the right, the indicated SWR is 2.0:1. The forward
power is 52 watts, the reflected power is 6 watts, and the two needles intersect on the red line
which indicates 2.0:1 SWR.
Rear Panel
The rear panel of the AT-1000 Pro features six connectors.
ANT 1 connector: Connect a 50-ohm coax antenna feedline to this standard SO-239
ANT 2 connector: Connect a second 50-ohm coax antenna feedline to this SO-239
connector, if you have a second antenna system.
GND connector (wing nut): Connect to antenna system ground.
Transmitter connector: Connect a 50-ohm coax jumper cable from this standard SO-239
connector to the ANT jack on the back of the amplifier.
Radio Interface connector: This 1/8” stereo jack connects to the optional radio interface
cable, which connects to the tuner port on the transceiver.
DC Power jack: Connect the 12V DC power cable to the 2.5mm x 5.5mm coaxial power
jack. Center pin is positive, 12V 1A.
The AT-1000 Pro tuner is designed for indoor operation only; it is not water resistant. If you
use it outdoors (Field Day, for example), you must protect it from the rain. The AT-1000 Pro is
designed for use with coax-fed antennas. If use with longwires or ladder-line-fed antennas is
desired, an external balun is required. Be sure the balun is rated for 1000 watts or greater.
Always turn your radio off before plugging or unplugging anything. The radio may be
damaged if cables are connected or disconnected while the power is on.
Connect the Transmitter jack on the rear of the AT-1000 Pro to the amplifier output, using
high-quality 50 ohm coaxial cable terminated in a PL-259 plug. Crimp-on PL-259’s should not
be used in this application; only properly soldered plugs will provide safe and reliable
performance. The coaxial cable should be rated for the maximum power output capacity of the
amplifier, and kept as short as is practical.
Connect the antenna system to the ANT 1 jack on the rear of the AT-1000 Pro, also using 50ohm coaxial cable rated at the maximum power output capacity of the amplifier. If a second
antenna system is used, connect that antenna system to the ANT 2 jack.
Attach the supplied DC power cable to the DC Power 12V 1A jack on the rear of the AT1000 Pro. Connect the other end of this cable to an 11-15V DC power source capable of
supplying 1A of current. The center pin and the red lead are positive.
Grounding the AT-1000 Pro tuner will enhance its performance and safety. LDG
recommends that you connect your tuner to a suitable ground using heavy gauge wire or metal
braid. A dedicated outdoor ground rod is best, but a nearby cold water pipe is sometimes
satisfactory. LDG strongly recommends the use of a properly installed, high quality lightning
arrestor on all antenna cable
The AT-1000 Pro is controlled mainly from the front panel buttons. Tuning requests may
also be made via the front panel TUNE/CALL button of a connected Icom transceiver, if the
optional transceiver interface cable is installed.
Each AT-1000 Pro button has a dedicated primary function, which is activated whenever the
button is pushed. In addition, some buttons have additional secondary functions that are activated
after first putting the AT-1000 Pro into FUNC mode. FUNC mode is activated by pressing and
holding the Power/Func button until all the front panel LEDs light up, then releasing it. The
Auto, Ant1, C Up, and Tune LEDs will begin flashing to indicate they are ready to accept a
command in FUNC mode.
Pressing Auto, Ant1, C Up, or Tune, while in FUNC mode, will actuate that button’s
secondary function. If no buttons are pressed within a few seconds, FUNC mode is automatically
Power / Func Button
The Power/Func button’s primary use is to turn the AT-1000 Pro “on” or “off”. “Off” is
really just an ultra-low-power standby mode. To turn the AT-1000 Pro on, simply press the
Power/Func button momentarily. To turn the AT-1000 Pro off, press and hold the Power/Func
button three seconds until the AT-1000 Pro turns off. All front panel LEDs and the meter
backlight will turn off. Press the Power button momentarily to turn the AT-1000 Pro on.
The Power/Func button also is used to enter FUNC mode, as described above. Press and
hold the Power/Func button until all the front panel LEDs light up, and then release.
Auto / Thresh Button
The Auto/Thresh button is used to switch between fully automatic tuning and semiautomatic tuning modes. If the Auto LED is lit, the tuner is in fully automatic tuning mode. This
means that any time the SWR exceeds the pre-set SWR threshold, a memory tuning cycle will
begin. If the Auto LED is extinguished, then the AT-1000 Pro is in semiautomatic tuning mode,
which means that the Tune button must be pressed in order to request a tuning cycle.
The AT-1000 Pro uses its SWR Threshold to determine when to begin an automatic tuning
cycle. If fully automatic tuning mode is on, then any time that the SWR exceeds this level during
transmit, the AT-1000 Pro will begin an automatic tuning cycle.
The SWR Threshold can be set by putting the AT-1000 Pro into FUNC mode and then
pressing the the Auto/Thresh button. The cross-needle meter will display the current SWR
threshold above which an automatic tuning cycle will begin, and the Auto/Thresh LED will
begin blinking to indicate that the AT-1000 Pro is now in SWR Threshold Set mode.
If the currently displayed SWR Threshold level is acceptable, simply press the Power/Func
button again to exit SWR Threshold Set mode. Otherwise, press the Auto/Thresh button
repeatedly to cycle through the available choices of SWR Threshold level. The available levels
are 1.5:1, 1.7:1, 2.0:1, 2.5:1, and 3.0:1. Repeatedly pressing the button will cycle through all the
choices, and then back to the beginning again. Once the desired level is displayed on the crossneedle meter, press the Power/Func button to select the displayed level and exit SWR Threshold
Set mode.
Ant1 / Scale Button
The Ant1/Scale button is used to choose which connected antenna is active. If the ANT1
LED is lit, then Antenna 1 is selected. Otherwise, Antenna 2 is selected. Pressing the Ant1/Scale
button repeatedly will toggle the selected antenna.
The AT-1000 Pro’s cross-needle meter can display forward power up to 1000 watts, but
sometimes it is handy to be able to see lower-powered transmission levels with greater detail.
Pressing the Ant1/Scale button, while the AT-1000 Pro is in FUNC mode, will enter into the
Meter Scale Selection mode. Put the AT-1000 Pro into FUNC mode as described above, and
then press the Ant1/Scale button. The Ant1 LED will begin blinking, and the forward power
meter will display the current meter scale setting.
A display of 10 indicates the meter is in the 0-100W scale. A display of 100 indicates that the
meter is in 0-1000W scale. Pressing the Ant1/Scale button repeatedly will toggle between these
two scales. Once the desired meter scale is displayed, press the Power/Func button again, to exit
Meter Scale Selection mode.
C Up / Peak Button1
Pressing the C Up button will increase the capacitance in parallel with the load by one unit.
Pressing and holding the C Up button will rapidly increase the capacitance. If the maximum
capacitance value is met, the C Up button will blink.
The secondary function of the C Up / Peak button is to toggle between average power
reading and peak power reading on the cross-needle meter. To select the metering mode, first
press and hold the Power/Func button until the front panel LEDs light up, then release, to enter
into FUNC mode. Then press the C Up / Peak button to select whether average or peak power
is displayed. When average mode is selected, the Forward power needle will bounce quickly.
When Peak mode is selected, the Forward power needle will go to full scale and stay there for a
moment, fall back to zero and repeat. Pressing C Up / Peak repeatedly will toggle between
these two modes. Press Power / Func again to set and exit.
The front panel of the AT-1000 Pro does not have a “Peak” label on the C Up button, as the peak reading feature was introduced after
the initial release of the AT-1000 Pro hardware.
C Dn Button
Pressing the C Dn button will decrease the capacitance in parallel with the load by one unit.
Pressing and holding the C Dn button will rapidly decrease the capacitance. If the minimum
capacitance value is met, the C Dn button will blink.
L Up
Pressing the L Up button will increase the inductance in series with the load by one unit.
Pressing and holding the L Up button will rapidly increase the inductance. If the maximum
inductance value is met, the L Up button will blink.
L Dn Button
Pressing the L Dn button will decrease the inductance in series with the load by one unit.
Pressing and holding the L Dn button will rapidly decrease the inductance. If the minimum
inductance value is met, the L Dn button will blink.
The L Dn button has no secondary function.
Tune/Store Button
The Tune/Store button is used for three functions: selecting bypass/active mode, requesting
a tuning cycle, and manually storing tuning settings in the tuner memory.
Bypass/Active Mode: Press the Tune/Store button momentarily to toggle between bypass
and active mode. In bypass mode, all inductance and capacitance is removed from the circuit.
Active mode restores the previous inductor and capacitor settings. The Tune/Store LED blinks
once to indicate active mode, and blinks three times to indicate bypass mode.
Request a Tuning Cycle: Press and hold the Tune/Store button to initiate a tuning cycle.
There are two types of tuning cycles available, a memory tune and a full tune. Hold the
Tune/Store button until the Tune LED comes on in order to select a memory tune cycle. Hold
the Tune/Store button until the Tune LED comes on, and continue holding until the Tune LED
goes out again in order to select a full tuning cycle. See the section on “Operation” for more
Manually Store Tuning Settings: Press and hold the Power/Func button until the front
panel LEDs light up to put the tuner in FUNC mode, then press the Tune/Status button to
manually store the current inductor and capacitor settings in the memory associated with the last
transmitted frequency.
The AT-1000 Pro uses two different tuning cycles. The memory tuning cycle attempts to
tune quickly based on having previously tuned on the present frequency selection. If the tuner
previously was successful in tuning on the currently selected frequency, the settings for that
match will be loaded into the tuner relays, and checked to see that an acceptable SWR match is
found. This makes memory tuning almost instantaneous.
A full tuning cycle “starts from scratch” and begins a fixed tuning sequence where the AT1000 Pro rapidly tries varying combinations of inductance and capacitance values, and then
zeroes-in on the best match possible. When the tuning cycle is complete, if an acceptable match
was found, the inductance and capacitance settings are saved in a memory associated with the
selected frequency, so that they may be recalled quickly in the future via a memory tuning cycle.
In this manner, the AT-1000 Pro “learns”; the longer you use it, the more closely it adapts
itself to the bands and frequencies you use. Most users will probably use memory tuning most of
the time; it takes advantage of any saved tuning settings, but automatically defaults to a full
tuning cycle if no stored data is available.
In both cases, at the end of the tuning cycle, the carrier is held for 1.5 seconds after tuning is
complete, so that the final SWR may be read on the transceiver’s internal SWR meter and the
built-in cross-needle SWR meter, and the front panel LEDs will indicate the status of the tuning
A Word About Roll-Back Circuits
Most modern amateur radio exciters with solid-state finals normally employ an automatic
“roll-back” circuit, which protects the final amplifier transistors from high SWR. This circuit
automatically reduces the output power as the SWR level rises above a preset level; often 2:1.
The higher the SWR, the more the roll-back circuit reduces output power in order to prevent
damage to the final transistors in the exciter.
If your exciter employs a roll-back circuit, you need not worry about damaging your exciter
while tuning, at any power level between 5 and 125 watts. However, if your exciter lacks a rollback circuit, the power level must be set manually to 30 watts or less before tuning, in order to
avoid damage to the exciter or the tuner. The exciter’s owner’s manual is a great place to check
to see if the exciter employs a roll-back circuit.
Fully Automatic Mode
If the tuner is in Fully Automatic tuning mode, ensuring that the minimum SWR condition is
met is simple. When changing operating frequency, simply bypass your amplifier, and transmit a
carrier. If the SWR exceeds the SWR Threshold, an automatic tuning cycle will begin. Once the
tuning cycle is complete, it is then okay to switch your amplifier back on and transmit at full
The AT-1000 Pro has built-in relay protection, so that tuning will not be permitted if
conditions exceed those allowed for tuning. If tuning is attempted while transmitting more than
150 watts when the SWR is over 3:1, or if transmitting over 200 watts at any SWR, the AT-1000
Pro will abort the current tuning cycle, so as to avoid relay arcing.
When not tuning, the cross-needle meter on the AT-1000 Pro will display peak forward
power and instantaneous reflected power. If the 100W meter scale is selected, and more than 125
watts of forward power are present, the front panel LEDs will blink to indicate the over-range
Semi-Automatic Tuning: Request Memory Tune Cycle
To request a memory tuning cycle, press and hold the Tune/Store button until the Tune LED
lights, then release. Begin transmitting a carrier of less than 75 watts (bypass the amplifier).
When the tuning cycle is complete, the front panel LEDs will blink to show the status of the
tune, and the cross-needle display will show the final SWR. If a satisfactory match is not found
in memory, a full tuning cycle will begin.
Semi-Automatic Tuning: Request Full Tune Cycle
To request a full tuning cycle, press and hold the Tune/Store button until the Tune LED
lights, then keep holding until the Tune LED extinguishes again, then release. Begin transmitting
a carrier of less than 75 watts.
When the tuning cycle is complete, the front panel LEDs will blink to show the status of the
tune, and the cross-needle display will show the final SWR. If a satisfactory match is not found,
a full tuning cycle will begin.
Although the AT-1000 Pro attempts to achieve the lowest possible SWR, there are times
when it might be desirable to manually tweak the tuning parameters to arrive at a better match.
Fortunately, the AT-1000 Pro provides complete manual control over all the tuning parameters,
and allows the user to store a manually tweaked tuning to memory for later recall.
Manually Adjusting Tuning Parameters
Use the L Up, L Dn, C Up, and C Dn buttons to increment or decrement the amount of
inductance or capacitance used to match the antenna. Press each button momentarily to increase
or decrease by one step, or hold the button to continuously increase or decrease inductance or
capacitance rapidly. The setting will change slowly at first, then rapidly as the button is held
longer. The button’s LED will blink when the limit of inductance or capacitance is reached.
The AT-1000 Pro uses an L-network for tuning. In order that a broader range of antenna
loads may be matched, a relay allows switching the capacitance arm of the L from the transmitter
side of the inductor bank to the antenna side of the inductor bank. This selection, too, may be
manually controlled.
To select the setting which corresponds to higher impedance antennas, press the C Up and L
Up buttons simultaneously, then release. The C Up and L Up LEDs will blink to confirm.
To select the setting which corresponds to lower impedance antennas, press the C Dn and L
Dn buttons simultaneously, then release. The C Dn and L Dn LEDs will blink to confirm.
SWR can be checked while making fine adjustments. Be sure to bypass the amplifier first,
then begin transmitting a carrier. Watch the cross-needle meter while making adjustments, and
observe the SWR.
Storing Manually Adjusted Tuning Parameters
Once the tuning parameters are adjusted as desired, these settings can be stored in a memory
location associated with the last transmitted frequency. To store the tuning parameters, put the
AT-1000 Pro into FUNC mode by pressing and holding the Power/Func button until front panel
LEDs light up, then release. While in FUNC mode, press the Tune/Store button. The Tune LED
will blink to confirm the storage of the parameters.
Various error or warning conditions are indicated by the front panel LEDs.
MARS/CAP Coverage
The AT-1000 Pro provides continuous tuning coverage over its specified range; not just in
the ham bands. This makes it useful for MARS or CAP operation, or any other legal HF
Icom Radio Interface
The AT-1000 Pro offers integration with many Icom transceivers, including the IC-7000 and
IC-706. Simply plug the 1/8” plug of the optional Icom interface cable into the Radio Interface
jack on the back of the AT-1000 Pro, and plug the 4-pin Molex plug into the matching jack on
the back of the radio.
Tuning can then be performed by first bypassing the amplifier, and then pressing and holding
the TUNE/CALL button on the Icom radio for 1 second. When tuning is complete, the amplifier
may be placed in active mode again. Momentarily pressing the TUNE/CALL button on the
radio after the AT-1000 Pro has tuned will place the AT-1000 Pro in bypass mode.
Optional Yaesu Radio Interface
The AT-1000 Pro also offers integration with Yaesu FT-857, and FT-897 transceivers. Plug
the black end (marked “Tuner”) of the optional Yaesu interface cable into the Radio Interface
jack on the back of the AT-1000 Pro, and plug the red end (marked “Radio”) into the ACC jack
on the back of the FT-857 or FT-897.
Tuning operation is the same as described in the section on Basic Tuning, except that when a
manual memory tune or full tune is requested, the AT-1000 Pro will send a signal to the FT-857
or FT-897 requesting that the radio begin transmitting a low level carrier. Once again, be sure to
bypass the amplifier before requesting a tuning cycle in this case, and then re-activate the
amplifier once the tuning cycle is complete.
Build-Your-Own Interface
The Radio Interface jack on the rear of the AT-1000 Pro follows the same format as most
Icom transceivers’ Tuner interface. The
1/8” stereo jack features a Start input,
which requests that the AT-1000 Pro
begin a tuning cycle when this input is
grounded momentarily (450-600 ms). It
also features an open-collector Key
output, which the AT-1000 Pro shorts to
ground when it is requesting that the radio
should key up and transmit a carrier.
Some basic ideas about impedance
The theory underlying antennas and transmission lines is fairly complex, and in fact employs
a mathematical notation called “complex numbers” that have “real” and “imaginary” parts. It is
beyond the scope of this manual to present a tutorial on this subject2, but a little background will
help in understanding what the AT-1000 Pro is doing, and how it does it.
In simple DC circuits, the wire resists current flow, converting some of it into heat. The
relationship between voltage, current, and resistance is described by the elegant and well-known
“Ohm’s Law”, named for Georg Simon Ohm of Germany, who first discovered the principle in
1826. In RF circuits, an analogous but more complicated relationship exists.
RF circuits also resist the flow of electricity. However, the presence of capacitive and
inductive elements causes the voltage to lead or lag the current, respectively. In RF circuits, this
resistance to the flow of electricity is called “impedance”, and can include all three elements:
resistive, capacitive, and inductive.
The output circuit of a transmitter consists of inductors and capacitors, usually in a
series/parallel configuration called a “pi network”. The transmission line can be thought of as a
long string of capacitors and inductors in series/parallel, and the antenna is a kind of resonant
circuit. At any given RF frequency, each of these can exhibit resistance, and impedance in the
form of capacitive or inductive “reactance”.
Transmitters, transmission lines, antennas, and impedance
The output circuit of a transmitter, the transmission line, and the antenna, all have a
characteristic impedance. For reasons beyond the scope of this document, the standard
impedance is nominally 50 ohms resistive, with zero capacitive and zero inductive components.
When all three parts of the system have the same impedance, the system is said to be “matched”,
and maximum transfer of power from the transmitter to the antenna occurs. While the transmitter
output circuit and transmission line are of fixed, carefully designed impedance, the antenna
presents 50-ohm, non-reactive load only at its natural resonant frequencies. At other frequencies,
it will exhibit capacitive or inductive reactance, causing it to have an impedance other than 50
For a very complete treatment of this subject, see any edition of the ARRL Handbook for Radio Communications (previously the
Handbook For Radio Amateurs).
When the impedance of the antenna is different from that of the transmitter and transmission
line, a “mismatch” is said to exist. In this case, some of the RF energy from the transmitter is
reflected from the antenna back down the transmission line and into the transmitter. If this
reflected energy is strong enough, it can damage the transmitter’s output circuits.
The ratio of transmitted to reflected energy is called the “standing wave ratio”, or SWR. An
SWR of 1 (sometimes written 1:1) indicates a perfect match. As more energy is reflected, the
SWR increases to 2, 3, or higher. As a general rule, modern solid state transmitters must operate
with an SWR of 2 or less. Tube exciters are somewhat more tolerant of high SWR. If a 50 ohm
antenna is resonant at the operating frequency, it will show an SWR close to 1. However, this is
usually not the case; operators often need to transmit at frequencies other than resonance,
resulting in a reactive antenna and a higher SWR.
where F = Forward power (watts), R = Reflected power (watts)
SWR is measured using a device
called an “SWR bridge”, inserted in
the transmission line between the
transmitter and the antenna. This
measures forward and
reflected power from which SWR
may be calculated (some meters
calculate SWR for you). More
advanced units can measure forward
and reflected power simultaneously,
and show these values and SWR at
the same time.
An antenna tuner is a device used
to cancel out the effects of antenna
reactance. Tuners add capacitance to
cancel out inductive reactance in the
antenna, and vice versa. Simple
tuners use variable capacitors and
inductors; the operator adjusts them
by hand while observing reflected
power on the SWR meter until a
minimum SWR is reached. The LDG
Electronics AT-1000 Pro automates this process.
No tuner will fix a bad antenna. If the antenna is far from resonance, the inefficiencies
inherent in such operation are inescapable; it’s simple physics. Much of the transmitted power
may be dissipated in the tuner as heat, never reaching the antenna at all. A tuner simply “fools”
the transmitter into behaving as though the antenna were resonant, avoiding any damage that
might otherwise be caused by high reflected power. For best performance, the antenna used
should always be as close to resonance as is practical.
In 1995, LDG Electronics pioneered a new type of automatic antenna tuner. The LDG design
uses banks of fixed capacitors and inductors, switched in and out of the circuit by relays under
microprocessor control. An additional relay switches between high and low impedance ranges. A
built-in SWR sensor provides feedback; the microprocessor searches the capacitor and inductor
banks, seeking the lowest possible SWR. The tuner is a “Switched L” network, consisting of
series inductors and parallel capacitors. LDG chose the L network for its minimum number of
parts and its ability to tune unbalanced loads, such as coax-fed dipoles, verticals, Yagis, and, in
fact, virtually any coax-fed antenna.
The series inductors are switched in and out of the circuit, and the parallel capacitors are
switched to ground under microprocessor control. The high/low impedance relay switches the
capacitor bank either to the transmitter side of the inductor bank, or to the antenna side. This
allows the AT-1000 Pro to handle loads that are either greater than or less than 50 ohms. All
relays are sized to carry 125 watts continuously.
The SWR sensor is a variation of the Bruene circuit. This SWR measuring technique is used
in most dual-meter and direct-reading SWR meters. Slight modifications were made to the circuit
to provide voltages instead of currents for the analog-to-digital converters that provide signals
proportional to the forward and reflected power levels. The single-lead primary through the
center of the sensor transformer provides RF current sampling. Diodes rectify the sample and
provide a DC voltage proportional to RF power. These two voltages are read by the ADCs in the
microprocessor, and are used to compute SWR in real time.
The relays are powered by the 12VDC input provided by the optional radio interface cable.
This power is supplied by the transceiver itself. The relays are a latching type, and so they
consume no current when not actively switching.
Although the microprocessor’s oscillator runs at 32 MHz, which allows the main tuning
routine to execute in only a few milliseconds, the relays require several milliseconds of settling
time for every combination of inductors and capacitors. Thus, it may take several seconds before
all relay combinations are exhausted, in the case of a difficult tune.
The tuning routine uses an algorithm to minimize the number of tuner adjustments. The
routine first de-energizes the high/low impedance relay if necessary, then individually steps
through the inductors to find a coarse match. With the best inductor selected, the tuner then steps
through the individual capacitors to find the best coarse match. If no match is found, the routine
repeats the coarse tuning with the high/low impedance relay energized. The routine then fine
tunes the inductors and capacitors. The program checks LC combinations to see if a 1.5:1 or
lower SWR can be obtained, and stops when it finds a good match.
The microprocessor runs a fine tune routine just after the tuner finds a match of 1.5:1 or less.
This fine tune routine now tries to the the SWR as low as possible (not just to 1.5); it takes about
half a second to run.
Be sure to use a vacant frequency when tuning. With today’s crowded ham bands, this is
often difficult. However, causing interference to other hams should be avoided as much as
possible. The AT-1000 Pro’s very short tuning cycle, as little as a fraction of a second,
minimizes the impact of tuning transmissions.
The AT-1000 Pro tuner is essentially maintenance-free. Power limits in this manual should
be strictly adhered to. The outer case may be cleaned as needed with a soft cloth slightly
dampened with household cleaning solution. As with any modern electronic device, the AT-1000
Pro can be damaged by temperature extremes, water, impact, or static discharge. LDG strongly
recommends the use of a good quality, properly installed lightning arrestor in the antenna lead.
The LDG customer support staff is ready to answer your product question by telephone and
by e-mail. We know that you will enjoy your product even more knowing LDG is ready to
answer your questions as the need arises.
LDG regularly updates on-line information so the best on-line support information is
available all day and every day.
The LDG website provides links to product manuals, just in case you lose this one! When
you are thinking about the purchase of other LDG products our website also has complete
product specifications and photographs you can use to help make your purchase decision. Don’t
forget the links to all of the quality LDG Dealers also ready to help you make that purchase
Your product is warranted against manufacturer defects in parts and labor for two full years
from the date of purchase. This two-year warranty is also transferable. When you sell or give
away your LDG product, give the new owner a copy of the original sales receipt and the twoyear warranty goes with the new owner.
There is no need to complete a warranty card or to register an LDG product. Your product
receipt establishes eligibility for warranty service, so save that receipt. Send your receipt with the
product whenever you send your product to LDG for repair. Products sent to LDG without a
receipt are considered requests for out-of-warranty repair.
LDG does not warranty against product damage or abuse. This means that a product failure,
as determined by LDG, to be caused by the customer or by other natural calamity (e.g. lightning)
is not covered under the two-year warranty. Damage can be caused by failure to heed the
product’s published limitations and specifications or by not following good Amateur practice.
If a product fails after the warranty period, LDG wants to help you get it fixed. Send
the product to us for repair any time you like. We will determine what needs to be done
and based on your instructions, either contact you with an estimate or fix it and contact
you with a request to pay any repair charges.
Returning a product to LDG is easy. We do not require a return merchandise
authorization, and there is no need to contact LDG to return your product. Visit the LDG
web site and download the LDG Product Repair Form. On the Repair Form tell the LDG
technicians exactly what happened or didn’t happen and why you believe the product
needs servicing. The technician attempts to duplicate the problem(s) you had based on
how well you describe it so take the time to be accurate and complete.
Ask your shipper for a tracking number or a delivery verification receipt. This way
you know the product arrived safely at LDG. Be sure to give us your email address so our
shipper can alert you online when your product is en-route back to you. Please be assured
that our staff makes every effort to complete repairs ahead of our published wait time.
Your patience is appreciated.
Repairs can take six to eight weeks, but are usually faster. The most recent
information on returning products for service is found on the LDG website under
Support, then Tech Support. Send your carefully packaged unit with the Repair Form to:
LDG Electronics, Inc.
Attn: Repair Department
1445 Parran Rd
St. Leonard, MD 20685
We encourage product feedback! Tell us what you really think of your LDG product. In a
card, letter, or email (preferred) tell us how you used the product and how well it worked in your
application. Send along a photo or even a schematic or drawing to illustrate your narrative. We
like to share your comments with our staff, our dealers, and even other customers at the LDG
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