You probably have a preamp on your rx loop. The first thing to do is kill the dc to it on transmit to shut it down. I have an Airspy HF+Discovery SDR which has a fragile front end. To keep tx RF out of it, in addition to shutting down the preamps, I put a pair of coax relays in series, the little ones with SMA jacks on them, between the antenna feed and the SDR. I used a pair because each had 12 v. coils, and my sequencing system runs on 24 v. I also put the SDR in a metal box and put pie wound chokes in series with the DC control lines into the box. As I recall, that was enough to protect the SDR. A lot depends on prox of tx antenna to rx antenna and also tx antenna relative to shack. If all are spread out, job is much easier. I also used an ice cube relay in the feedline to break open both the center conductor and shield to interrupt RF on the outside of the shield. I looked at the commercial rx protectors (not the one posted here by a fellow in the U.K.) and the specifications were not sufficient for the Airspy.
Rob K5UJ _________________ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
