By Matt Erickson KK5DR
Oct. 2004.
These little auto whip/wire tuners have been on the market for a few years, but I
have recently acquired a new one for use with my IC-746Pro in a field type
operation.
Above is a picture of the tuning unit, shown with the plastic cover installed. The
entire body of the cover is plastic, with chrome plated metal mounting plates
screwed to the back half on top and bottom. The unit is fully weather tight, with
seals on every seam.
Above is a picture of the internal parts of the tuner unit. Notice the rubber gasket
that seals the two halves of the cover. There are also seals on all the cable entry
ports as well as the ground lug, and the output insulator. In the center of the
photo, can be seen, the input coax cable connector. Next to the coax input port is
the ground line attached to the external ground lug. On the right hand side of the
picture is a short red wire which is the RF output line to the antenna insulator.
The AH-4 uses relay switched LC networks for matching of the output antenna.
There are 1,040,000 possible LC combinations that are selected by the CPU in 2.5
seconds or less. The unit is designed to operate from 3.5 to 54MHz, with a
wire/whip of 23ft. long or more. For operations on 7-54MHz only, and shorter
radiating wire/whip can be used. If the unit is to be used in a mobile installation,
the ground should be a heavy strap bonded to the frame of the vehicle, and the
tuning unit should be mounted as close to the whip as possible, preferably with a
feed length of 12" or less to the whip. The CPU is shielded in the silver box in the
upper left of the photo above. At the upper center is a gray terminal strip where
the control cable is to be connected. While the unit is powered up, there are 45
memories that are automatically saved after a tune cycle on a given frequency,
after that, the unit uses the memorized settings to retune each time the transmitter
is keyed, in under 1 second. When the unit is powered down, the memories are
lost.
The AH-4 is rated at 125 watts input maximum. It is recommended that either a
heavy ground strap be used in a mobile installation, or on portable/field operation
should use a set of at least three counterpoise wires of equal length to the radiator
antenna. I plan a set of four wires about 30' long each for counterpoise, and a 30'
wire for antenna. The control cable is only 16' long, I wish it was twice that long,
to get the unit farther away from the radio, and the operator.
I made a special RF input cable with the addition of a toroid cores that will choke
off any RF current returning to the radio on the outside of the coax or the control
cables.
One small potential problem I could see, would be the formation of water
condensation inside the tightly sealed unit when operating outdoors in all types of
weather. A simple fix is to place a small packet of silica gel inside the unit before
it is sealed up. This packet will absorb any trapped water vapor inside. Changing
or recharging the silica gel pack about once every few years would be a good
idea. I have found that silica gel can be "recharged" by placing it in a gas type
kitchen oven with only the pilot light on. Leave the pack there for about 5-7 days,
and the gel should be recharged by then.
Field test
My first test of the AH-4 was using a single 12ga. insulated stranded wire for the
antenna 30' long, pulled up into a tree just off my porch. The counterpoise system
uses the same wire, but there are four of them at 30' long each. The exciter must
be placed in CW mode to tune the AH-4, it tunes at a reduced output
automatically. I used my IC-746Pro as the exciter for the AH-4. The antenna port
#1 must be used since when the unit is connected to the exciter, the internal ATU
is automatically bypassed and "EXT" is displayed on the front panel display. It
only works through ant port #1 for HF/50MHz.
I started on 17mtrs, but due to the poor conditions these days my calls went
unanswered, same on 15mtrs. In this time of low sunspots and weak propagation
on the higher frequency bands, some times the more effective bands are below
20mtrs. I went to 40mtrs where I found strong daytime activity, and my signal
was reported to be good, very readable. No RF feed-back was detected, thanks in
part to my toroid chokes and good ground plane created by the counterpoise
system. Tuning was quick, under 1 second, and the memories worked fine. I was
able to hop from band to band once the tune points were memorized on each
band. The longest tune time I noted was about 2.5 seconds. It is too bad that the
RAM is "volatile" meaning that when the unit is powered down all memorized
tune points are lost. Perhaps someday an updated AH-4 design will have "nonvolatile" RAM memory.
I consider the field test to be successful, even with the poor conditions. It proves
that this system can be used very easily when backpacking, camping, or on Field
Day. Its quick and easy, and fairly effective.
Field Day 2006:
We used the AH-4 on FD with an IC-7000. The radiating wire was 90 feet of
12ga insulated stranded copper. The ground radials were the same wire but cut to
30 feet, with four runs laid out in a fan pattern in the opposed direction from the
radiator wire. The radiator was about 15-20 feet above ground running horizontal.
The system worked very well, tuned very quickly and seemed to radiate very
well. The bands used were 80-10mtrs.
There were no problems with the tuner or radio during the entire event.
Conclusion
The AH-4 is a nice little package, excellent for mobile whip tuning, and
backpacking, as well as QRP remote antenna operations. I don't really like the
short control cable, it should be at least 25' long so when operating a ground
mounted vertical, the radio can be located somewhat out of the main radiation
field, but with the 16' cable, the operator is nearly on top of it.
I added 25 feet of four conductor unshielded cable to the control cable with the
connector installed on the radio end of it. I added about 40 feet of coax to feed the
tuner. Now the unit can be placed a good distance from the operating position, or
high in a tree.
I plan to use my AH-4 when I'm out camping, and on Field Day, for quick and
easy to install 80-6 meter antennas. The unit tunes quickly and nearly flat,
typically 1.2 or less.
Tiny, quick, and easy to install and use.
To learn how tuners/couplers work click
73 de Matt
Copyright © 2006 M.A. Erickson, KK5DR. All rights reserved.
here.
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