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SDR Antenna Switch Up and Running

sdr antenna switch

My remote control SDR antenna switch is up and running. Now, I can switch SDR and antennas by remote control.

You may think it’s ugly, but it works. Mounted on the wall behind my operating desk. On the right, you can see my loop array control box. In the center is my SDR antenna switch. On the left, three receivers. All controlled by an Arduino over RS-232.

With this setup, I can switch antennas between multiple receivers, including several dual channel radios for modern diversity reception. These include RSPduo, Afedri AFE822x and ANAN-7000. In addition to the loops, antenna inputs include my main ham antennas and noise probes.

Mechanically and electrically, everything works. But I have some RFI ingress problems, which I will tackle shortly. Other than the RFI, everything seems close to perfect.

When I started this project, RFI ingress was my biggest fear. Would the relays pick up power supply noise? Would my Arduino provide hash in addition to its 16 MHz oscillator? Would there be enough isolation between the relay switches.

Over the next week or so, I will do extensive testing to see if I can find and eventually solve the problem.

SDR Antenna Switch – Remote Control

I wrote a small Windows application to let me control everything from my radio computer. Shown below, I can switch pairs of channels to different receivers, select antennas, and control the two active loops.

It’s been a few years since I have written any Windows code. But, I got back up to speed real fast with Delphi 10.4 Community Edition. My control program took only a day to code and debug.

With Delphi, making a GUI is easy and mostly visual. My application connects to the Arduino over RS-232 using the USB connection. Changing a GUI control creates an “event”, which triggers an ASCII command to the Arduino. I wrote a simple text protocol to control the SDR antenna switch remotely.


  1. VE6KK says:

    Nice work John! Is there a way to put the Arduino to sleep or use a micro which will? At least in between antenna selection things would be quiet.

  2. Mike says:

    Hi John, nice to see the accumulated success of all your determination. Not only does it work it looks great! It’ll be interesting to know the noise results when you get that done.

    Nice work!

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