Palstar AT-AUTO Mod

This is an interesting modification for the AT-AUTO. This mod adds a second SO-239 coaxial output in place of one the posts normally used for the “balanced” antenna output. It’s a Palstar AT-AUTO Mod that I think I may need one day. The instructions are simple and I found a few photos of modified units on the web.

I found this information on the Kessler Engineering website:

I have an AT-AUTO but I need a second coaxial output. Can I remove the balun and replace that with a second SO-239 connector? What is the best way
to do this? How would I know which coax output I’m using?

You have two options. We would prefer that you purchase the accompanying CX-AUTO which provides eight coaxial outputs. However, if you prefer to simply add a second coaxial output and don’t need the balanced output, we recommend the following procedure:

  1. Unsolder the balun lead at the antenna relay.
  2. Remove one of the balanced output connector “Bolts” and associated nylon insulating hardware.
  3. Insert an SO-239 connector in the vacated balanced output connector.
  4. Solder a #14 wire from the center-pin of the SO-239 connector to the relay contact which previously went to the balun.

If you follow these steps, this modification can readily be “undone” and no added holes, etc. will be necessary. The firmware will associate the “new” coaxial output with the “Balanced” memory settings, etc., and will be selected whenever “balanced” or “bal” is shown in the AT-AUTO display.

Palstar AT-AUTO Mod
I’ll use a ‘bulkhead’ type so-239 connector (like the others), not a panel mount. No drilling.

Here’s an inside view of the Palstar AT-AUTO Mod:

Palstar AT-AUTO Mod
The balun is disconnected and the jumper is installed in its place (lower left)

I currently have two HF wire antennas on the roof that I am not using. If I perform this mod on both of my AT-AUTO’s I could regain use of both of these antennas, a G5RV, and a second 130ft dipole (in a different direction than the ‘main’ dipole. aka [DIPOLE1]

Author: K6HR

Licensed since 1994. Active on HF / VHF / UHF / Satellite.

Leave a Reply