LDG AT-11MP Manual - page 4
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In either mode (Auto or Semi), if power (either RF or +12) is removed after the tuning cycle starts,
but before it finishes, the tuning will stop. The resultant tune will be undetermined; it may or may
not be a match.
In some extreme tuning cases, the power needle may waver while transmitting a continuous
carrier. This indicates that the tuner is near the tuning limits. You may be able to find a slightly
better tune with the manual adjustment toggle switches. Sometimes reducing power will provide a
better reading.
If reducing the RF power improves performance of the tuner, there may be RF getting into the
tuner through the DC power or ground system. Placing RF chokes on the DC line or RF line may
help reduce the RF interference.
In the presence of RF getting into the tuner, it is possible that the processor may lock up. In this
case the red LED and meter light will be on, but there may be little or no control. By removing,
then re-inserting the power plug on the rear panel, the processor will be reset and operation
should be returned to normal. If the problem persists, takes corrective measures as mentioned
above to remove the RF from getting into the tuner.
Performance
: The actual performance from the small package will surprise you. It really tunes a
lot of antennas to a lot of places! Here are some of the actual test results.
A 40-meter dipole (at 30 feet) would tune just about anywhere from 3.1 to 30 MHz! We had some
problems at 19 and 28 MHz finding a 1.5 match. The AT-11MP usually found a 2.0, and then we
had to use the manual switches to get below 1.5.
Next, an Antron-99 (at 40 feet) would again tune just about anywhere from 30 to 7 MHz. The auto
mode worked great the whole time. We just dialed down the band and the AT-11MP would kick in
whenever the SWR went over 3.0.
Then we tried out the unit on a 3-element tri-band (20,15,10) at 70 feet. It would tune any of the
ham bands (including WARC) except 160 and 80. We had some problems finding a match around
28.200 MHz, but got around it by moving to 28.150, letting the AT-11MP find a match, then moving
back to 28.200.
We’ve tried many other antennas with similar good results. There may be a place or two that your
antenna (dipole, inverted-Vee, vertical, beam, etc.) won’t tune. Also, the farther away from
resonance you try to tune, the harder time the tuner will have. The AT-11MP will tune a 10 meter
vertical to 80 meters, but your performance will not be that great (you can’t get something for
nothing).
For mobile operation, we find that a base or mid-loaded whip such as a Hamstick, Hamwhip, or
Hustler Resonator the tuner will find a match for the band that the antenna is cut for, plus one
band and minus one band. For example, a 20 meter antenna will usually tune 40, 20 and 15
meters (WARC bands included). A 102” CB whip will usually not tune anything except 10 and 15
meters.
For balanced lines and random wires, you may get better performance by using a 4 to 1 or 6 to 1
balun between the antenna and tuner. The optional RBA-1 4 to 1 balun is a good choice for an
external balun to match balanced lines or random wires.
The SWR bandwidth (usable bandwidth of 1.5 SWR without retuning) averaged about 200 kHz.
Not surprisingly, the bandwidth was smaller on the lower frequencies (about 75 kHz on 80 meters)
and larger on higher frequencies (about 400 kHz on 10). Insertion loss was highest on 10 meters
at about 0.1 db.