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Antenna Switch Port Isolation Considered

antenna switch port isolation

My homebrew antenna switch port isolation is decent, but not great. But too much RFI is being fed though the outputs.

In this post, I will check the port isolation on my basic Arduino controlled relay switcher. You can see the results and test setup pictured above.

My signal generator is set to put out a signal on 10 MHz. Signal level is about -10 dBm, or 200 millivolts. You may recall this is equivalent to a strong local BCB transmitter received with my wideband loops. My signal than passes through the antenna input relay switch, over a channel bus and through the output relay switch.

I set up my TinySA spectrum analyzer to sweep 2-20 MHz, and captured these sweeps on a computer in the lab.

On the top left, you can see the sweep with both relays switched on. I get a -10 dBm output signal with nearly no loss. Great. But look at the noise at the bottom of the trace! Oh, dear. (You can also see spikes at 12 MHz from my computer and especially 16 MHz from the Arduino clock oscillator.)

Now the antenna switch port isolation test. With the output relay disabled, signal drops to -40 dBm (center picture). Turning off the input relay, we see a drop to -65 dBm. So, basic antenna switch port isolation seems to be about 30 dB for each relay switch.

Antenna Switch Port Isolation with this Simple Design

As shown previously, my switch is constructed with very simple point to point wiring. Number 20 AWG wire connects the BNC center conductors to the relays. Metallic paint on the 3D printed box connects all the BNC grounds.

As you can see, I used normally open connectors on the output relays to connect a receiver to the antenna bus. Relays can be switched in parts to support these diversity receivers.

I might try using thin coax to improve the connects, and wire the ground terminals together properly to see if I can improve things.

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