Automatic antenna switching

I have a radio upstairs, which I use occasionally if the shack is uncomfortable.

There is a single coax running upstairs from the shack, which if I want to use the radio upstairs, I have to switch it in the shack, and change between HF and VHF by unplugging the coax and connecting it to the correct antenna.

Of course, I usually forget, and the antenna is not connected to the right room.
I had a similar situation in a previous shack where I needed to monitor an emergency frequency in another room.

I have been using this  for 5 years now (and a similar one without the dummy loads since 2012) and have not had any problems with the relays, I decided make up a very simple switch with the same type of relay, the normally close position feeds the upstairs radio, and the normally open side feeds the antenna switch in the shack.

As soon as I switch on any of the power supplies in the shack, the relay is activated and the antenna is fed to the shack, turn the power off, and it is fed upstairs, nothing to forget!


I have now added one to my 2m vertical, place a diplexer at both ends of the coax, and can use HF and VHF upstairs.

Not wanting it to be large, and to save metalwork, I used the bare relay with cables soldered straight onto the relay.

A copper wire “frame” acts as a stress relief to take any tension on the coax


The tails of the copper frame are twisted, it makes it stronger and gives the heat shrink tubing a better grip. All the braids are soldered on before putting the relay in the frame to avoid melting the relay case.


The centre conductors are slightly looped to ensure there won’t be any strain if the coax cabled are pulled.
I made another one for 2m, where I kept the wires as short as possible.
The relay terminals are bent flat to prevent them poking through the heat shrink covering.


Adhesive lined heat shrink is placed over the cables and frame tails.



A centre piece of heat shrink to cover the relay, ans two outer pieces to close the ends to preveny anything getting in to the relay terminals.



The finished switch