Amateur Radio

Simple full duplex relay switch

My setup for amateur radio satellites is SDR for receiving (RX) and Icom IC-705 for transmitting (TX). To my antennas I have two separate coax feedlines. Before, when switching band between RX and TX I was forced to manually change the coax feedlines connectors between SDR and IC-705.

I started to plan a simple relay switch to be able to switch fast and easy between TX/RX and UHF/VHF antenna – I call this a ”Simple full duplex relay switch”. The plan was this:

  • When no power to the relays the SDR is connected to the UHF antennas and IC-705 connected to the VHF antennas.
  • When 12V power to the relays the SDR is connected to the VHF antennas and IC-705 connected to the UHF antennas.

The relay used was this mini SMA relay by OK1CDJ. It can handle 10 watts (up to 20 watts according to hamshop.cz). The short coax between the relays are RG-405.
I have done SWR and loss measurements and it is very low. The original design and measurements can be found here:

This is the result, it works very good. Todo: put the relays in a nice box.

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