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Author Topic: Mods for the MFJ 1925 ATAS antenna tuner.  (Read 1604 times)
AA4F
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« on: June 27, 2004, 02:26:53 AM »

Modifications to the MFJ 1925 ATAS antenna controller.

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
lcox107@comcast.net

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