> If you are planning to use closely spaced Tx and Rx antennas, I would > suggest that you consider using a Reed relay or similar "fast acting" > relay > to short circuit the external preamp's input during transmit periods.
So long as the relay is accuated before RF appears, and held until after RF goes away. > Of course if diodes are used for protection instead of a relay, the diodes > could generate Tx harmonics which are then radiated by the Rx antenna. Worse yet diodes destroy dynamic range. A typical switching silicon diode or fast rectifier starts to conduct at about 2.5 dBm, and that can be from an accumulation of many signals...even out of Ham bands. It takes special circuitry to not reduce dynamic range with diodes. <<To reduce my bench time creating my own amplifier and such like I was looking into using the RPA-1 from DXEngineering which has an automatic bypass mode. I don't know if it will cope with QSK, but as a first stop that's what is in my mind to buy. >> It wasn't planned to do that. The relay would be held up by a capacitor as it discharges, but it could be modified. <<I think the spec says the RPA handles 30dBm signals as normal, so I'm thinking it will prevent damaging signals getting to the rx input.>> The RPA can output well over 1/2 watt, so don't expect it to act like a limiter. It makes a good QRP transmitter. 73 Tom ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
