[old sparks]

For locating interfering signals on UHF, I would suggest a cheap SDR dongle and have a listen on RF21. If you hear interfering signals, build or buy a small directional antenna and try to track them down.

I've purchased two of the cheap blue R820T2/RTL2832U ebay dongles and they work fine, but rtl-sdr.com sells a modded dongle that is good-to-go right out of the box, with an SMA connector...

 

[old sparks]

Do you mean just hook it up without an antenna and listen/look for interfering signals on RF21? Then if I find something, add a directional antenna? Which software do you recommend?

Listen and look, I guess. I think majortom and rabbit73 can explain better than I

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