> The Johnson T-R switch came in two iterations, as I recall. The first > one suffered from suck-out, as did the second, but less so.
Signal suckout occurs because the tank circuit in the transmitter presents a low impedance when the tube end of the tank is misterminated during key-up (resting or receiving) periods. Remember a tank circuit is also an artificial or lumped transmission line that often looks like it is 100-140 degrees long electrically, so the impedance at the end going to the 50 ohm cables can be very low when the tube is not conducting..shorting the transmission line for received signals. If you would have added around 40-80 degrees of extra coax between the rig and the T/R switch tap point it would have cured the signal suck-out. For a very short time I ran my B+ through the second unused blade of my knife switch so I could use one 300 volt supply for my receiver and transmitter. Good training in eye-hand coordination. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
