Antenna Switch


With the addition of a second radio into the shack the need to switch the rigs between the antenna became a problem. A simple and cheap solution would be to purchase a commercial antenna switch and use the switch backwards to operate the two rigs on one antenna. While that solution will work, there are some downsides to that arrangement. When one rig is switched to the antenna, the other rigs antenna connection is either left open or grounded. This becomes an issue if you forget the radio is connected to the open or grounded side of the switch and you try to transmit, it is very easy to damage the radio's finals.

With the recent addition of my homebrew dummy load to the shack the idea came to me, why not switch one radio to the antenna and one to the dummy load, this solves the problem of an open transmitter line. It also serves a double duty so I can manually switch the rigs to the dummy load when testing is needed.



I started off with a aluminum project enclosure from Radio Shack, the use of a metal enclosure will help with some shielding from RFI. My main coax connection to the antenna tuner is made with a BNC connector, the rest of the connections I used SO-239 connectors I had laying around. The Switch is from radio shack, and is rated at 250V 6A, it is a DPDT. I researched many homebrew switches before the build, and surprisingly the switches with less rating have been used with no problems. I only plan on putting 100 watts max through the switch on SSB and around 30 watts on digital.

Here is the schematic for the switch, it is a very simple circuit, the RF hot is switched and the ground or coax shields are all tied together. This is designed to switch between the rigs with the other rig turned off. I would not want to "Hot" switch the rigs on TX or even have the other rig on receive as the other was transmitting.

The holes for the connectors were drilled, and they were then mounted with machine screws to the enclosure. The front panel was then drilled for the switch.

I decided for the ease of wiring and remembering the rig configuration I would mount the DPDT switch sideways, instead of the typical vertical throw mounting.  Next all of the connections between the switch and coax connectors were made with very short sections of good quality RG-58 coax cable. All coax shields were bonded together to help with RF shielding.

 Once this was completed it was a simple continuity and resistance check to make sure all connections were solid. Then button up the housing, add the adhesive project feet. The last step is to label the connections, I used a sharpie pen I had laying around. Eventually I will invest is a electronic label printer and make the projects a little more professional.