Antenna Change Over Relay

The original relay was massive and as loud as hell. The antenna change over relay has a 110 volt coil and draws substantial current.  Try to connect this to the PTT line on a late model transceiver, and there is every chance your transceivers PTT line would not survive the voltage and or current demanded by this monster. 

The photo shows the amplifiers relay (with gas discharge tube). The comparison in size, to a vacuum and miniature relay is self evident.

The relay hot switched.  It often removed the antenna, prior to removing drive, or the tubes being cut off, hence the RF in the tank circuit suddenly had no load, and RF voltages would skyrocket.  In this situation arcs would occur in the tank compartment and the band switch was hammered.   This is very likely what so many hams have attributed to parasitic’s, but truth be known it is only due to the hot switching of the antenna changeover relay. Kenwood tried to tame things down a bit by putting the gas discharge arrestor on the relay for when things were going South, but it was ineffectual and not to be relied upon.


QSK was impossible, it could not switch fast enough.

There are a lot of ideas online that show guys replacing the relay with vacuum relays etc.  All manner of locations to fit them, as well as how to obtain the likely 24 volt control voltage required by most vacuum relays.  

  • Some were not interested in QSK and just used transistors or MOSFET’s to interface their radios to the standard TL-922 relay. It did not solve the noise issue nor did it fix hot switching. Not recommended in my opinion.
  • Others wanted QSK and perhaps like me, initially purchased the AG6K QSK kit. It had a small reed relay for the input switching and a vacuum relay for the output.
  • Still others installed vacuum relays for both input and output.
  • As time went by vacuum relays became more difficult to purchase and became increasingly expensive.


I finally got the neatest fix from Kessler Engineering. https://kesslerengineeringllc.com/tl922.html 

Don Kessler (KI6SZ) has put together a terrific kit, in that it covers many mods in addition to the antenna change over relay in one very neat package. It is an excellent commercial quality kit with outstanding installation documentation. I rate it highly and I have a dedicated page for it, under the “More Mods” menu drop-down item. If you haven’t done so yet, check it out. I am so glad I replaced my AG6K QSK kit with Don’s superb all in one kit.

Jack, (WB8BFS) https://www.wb8bfs.com/tl922mod.html has helped me with the input circuits of the amplifier. If you visit Jack’s website he details a number of mods he has undertaken. If you scroll down to the last mod in the list presented you will see “QSK EasyKey Modification”

Jack wanted to combine multiple upgrades along with his antenna change over. He describes it this way.

  • A single custom board to accomplish all of the following:
  • Key line compatibility with newer solid state radios,
  • Electronic 3-500Z bias switching,
  • QSK using a pair of RJ1A vacuum relays
  • and control of the front panel STBY and On Air lights (removing another noisy relay RL-2)

Jack is no longer supplying these kits. It certainly looks like a very neat and tidy unit. I don’t have personal experience with it but it had all the hallmarks of an excellent modification.

Image credit: WB8BFS