LDG AT-1000 Manual - page 6
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provided 2.5 x 5.5 mm coaxial power plug. Be sure to observe proper polarity; the center pin, and the red
lead are positive.
Basic Operating Instructions
Press the “Power” button on the front panel. The red LED above the button, and the meter lights come on
indicating that your AT-1000 has powered up and successfully completed a self-test. The tuner is now
ready to use.
Set your amplifier to standby, so it will not operate when you transmit; tune with your exciter only. Set
your exciter to transmit 20 watts (without rollback; see below), or up to 100 watts (with rollback) on the
frequency you plan to use. CW is usually the most convenient mode, but you can also use FM or an AM
carrier.
While transmitting 20 – 100 watts, momentarily press the “Tune” button on the tuner front panel; an
automatic tuning cycle will begin. You will hear the relays in your AT-1000 operate as they switch
inductors and capacitors in and out seeking a match; they make a fairly loud buzzing noise. You can
observe the present reflected power and SWR on the meter during the tuning process—but watch closely; it
happens fast! The tuning cycle will automatically end in a few seconds, with the meter indicating the final
achieved SWR, usually 1.5 or less. Check for an SWR of 2 or less. If the SWR is greater than 2, use the
manual adjustment buttons to adjust the SWR to level less than 2. Unkey your exciter.
Set your amplifier to operate, key your exciter and tune your amplifier as usual (if needed). Good practice
dictates tuning your amplifier into a 50-ohm dummy load with a suitable power rating. You may tune your
amplifier into the antenna through your AT-1000 providing it has tuned the antenna to a low SWR, and also
providing you do not exceed the specified ratings of either your amplifier or your AT-1000. Never press the
Tune button while transmitting more than 100 watts. Unkey when done; you are ready to transmit.
A word about “roll-back” circuits
Modern amateur exciters with solid state finals usually employ a “rollback” circuit to protect the final
amplifier transistors from high SWR, which can damage or destroy them. A rollback circuit senses the
SWR at the antenna terminal during transmit, and reduces the output power as the SWR rises above a
preset level, often 2:1. The higher the SWR, the lower the power is set to prevent damage.
If your solid state or tube-type exciter has a rollback circuit, you can simply key down and tune as
described above at any power level from 20 to 100 watts. If your exciter lacks a rollback circuit, you must
manually set the power level for tuning to 20 watts. At higher power levels, the reflected power
encountered during the tuning cycle could damage your exciter. Check your exciter owner’s manual to
determine if yours has a rollback circuit. Note that most Ten-Tec radios do not have rollback circuits.
Advanced Operating Instructions
Fine-tuning the tuner
In rare circumstances, the automatic tuning cycle will end with a relative high SWR, perhaps 1.5 or 2. This
is usually due to operation far from the antenna’s natural resonant frequency. You can manually adjust the
match using the Ind and Cap Up and Dn buttons on the front panel. While still transmitting with your
exciter after the automatic tuning cycle ends, you can press these buttons and observe the effect on SWR on
the meter.
Since you don’t know how the automatic tuning cycle set the inductors and capacitors, you will have to
make manual adjustments by trial and error. Press the Cap or Ind Up button three times and observe the
change in SWR. If it gets worse, tap the Dn button three times to return to your starting place, then try three