TX/RX relay

I was looking for a TX/RX relay that can work up to at least 100W and 6m.

Looking at some construction projects and the relays they use, it looked like you can more or less get away with murder compared to what is required on higher frequencies.

On one forum someone who builds linears professionally, claims they use JW1FSN-12V in linears up to several hundred watts. These are available off Ebay for around £3 or £4 so I thought I’d give it a go.

JW1SN-12V relay

A quick and dirty test (see pic to fully appreciate the quick-and-dirtiness of my unique approach) showed that it can carry up to at least 100W carrier on all HF bands with negligible loss. SWR was no worse than with only the dummy load connected.

Ditto wrt loss on 50MHz. SWR was slightly worse but still barely moved the needle. I only have a 2.5W source on 50MHz, so can’t comment on power handling.

Things fell apart on 2m SWR wise, which is not surprising (I again refer to the pic).

For now, my interest is only up to 6m, so this is fine.

Doing some calculations:

P = I*I*R

So, 100W in 50ohm:
Irms = sqrt(P/R) = 1.4A rms == 2A peak.

The relay is specified as:
AC: 10A/250V
DC: 10A/30V

According to the internet a good derating for a DC relay used for RF, is one fifth of the specified DC current. Well, that is rather convenient if not very scientific!

This is probably based more on peoples’ experience than anything else. And will also be affected by frequency. But I think this will do for the foreseeable future.



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