How to design a safe RF switch using latching relays?

Question

I'm working on a design for an RF switch using latching relays to switch two transceivers between four antennas. Each transceiver will be connected to at most one antenna at a time. But suppose one of the relays fails, and both transceivers are connected to the same antenna. This could result in damage to one of the transceivers.

What is the simplest way to prevent against this condition? Can I use one set of contacts on each relay to verify the state of each relay? I was thinking of doing something like this and applying AND or NAND to the control circuit based on the state of the relay's contacts.

I imagine there is a best practice for doing this but I haven't been able to find any write-ups about it.

Answer 1

^{simulate this circuit – Schematic created using CircuitLab}

Figure 1. Switching logic.

I have no idea how you would use relays in an antenna circuit but the logic you require is shown in Figure 1. It uses only two changeover relays - one single-pole and one two-pole.

How to design a safe RF switch using latching relays?

You don't explain why you need them to latch.

I was thinking of doing something like this and applying AND or NAND to the control circuit based on the state of the relay's contacts.

If the electronics fails then your circuit fails in an unsafe manner.

Answer 2

But suppose one of the relays fails, and both transceivers are connected to the same antenna.

You design the transmitters to only transmit the power they are supposed to and if something is taking to much (or too little) current then you detect this condition by monitoring the power rails to the transmit power amps.

In other words protect it by making it reliable under fault conditions. The monitoring of current for each transmit PA can tell your control circuit if there's a problem with the relays.