I have a mobile set up with the Icom 706 Mk IIG,
a Yaesu ATAS 120 antenna and an MFJ 1925
controller for the antenna. This makes a sweet
mobile station!
A couple things about the MFJ controller
bothered me and I came up with two modifications
to make it work better. The first problem is the
controller keys the rig all the time a frequency
change is being made. Changing from 20 meters to
40 meters takes about 15 seconds for the coil to
move the necessary distance. The rig is
transmitting the entire time. This problem can
be fixed with a small SPST switch installed in
the front of the box. Mount it near the end and
between the MFJ logo and ATAS. This switch
interrupts the white wire in the box, from the
control cable to the large rocker switch. With
the added switch in the OFF position the antenna
can be tuned for peak noise and turned ON for
the final tune up.
The second problem is the rig is unkeyed as soon
as the up/dn switch is released. You can not be
sure you did not pass the point of lowest SWR.
This is fixed by installing a 1000 mf. capacitor
across the rocker switch. The large rocker
switch is soldered through the circuit board on
the opposite end from the control cable and has
6 large pins. Use 2 of the 3 pins next to the
end of the board. The capacitor is connected
between the center switch pin and one of the
other 2 pins. This lets the radio remain keyed
about 2 seconds after the rocker switch is
released.
With the added switch and capacitor you can
minimize your transmitting time and QRM while
tuning the antenna. The delayed return to
receive lets you be sure the antenna is tuned to
the right place. I have enjoyed using my
controller with these mods and think you will
too!
Les, AA4F
The small toggle switch
interrupts the white wire from the control
cable.
This is the keying circuit
for the radio.
I used two 470 Mfd,
35 Volt capacitors in parallel. These are
available from
Radio Shack. Connect
between the center post on the rocker switch to
either
end connector. Shown
here it is attached to the pad for the resistor
behind
the black wire.
Position capacitors so box cover will fit!
