I live about 1 km from a site that used to have a 50 kW AM transmitter operating on about 1 MHz. I was using a vertical antenna at the time. I had problems with it breaking through on various bands. The attenuator in my K3 did not help. I discussed this with someone at Elecraft and it was suggested that the signal was strong enough to override the bias on the t/r switch diodes, which of course are before the attenuator. I made a 2.5 MHz high pass filter and it solved the problem. Later I switched to a horizontal dipole, and I could operate without the filter.
Victor 4X6GP On Sat, Jun 28, 2025, 04:01 Howard Hoyt via Elecraft < [email protected]> wrote: > Hi folks, > > For Field Day we have a K3 with the upgraded synth and a K3S, each has a > 3rd order Cauer elliptical bandpass filter but they are operating with > antennas in close proximity. The only interference we can see is when > either one is transmitting on 40m and the other receiving on 20m. > Obviously we are listening far away from 2nd harmonic, which comes in at > S9+20 dB, but we get S7 interference everywhere else in the 20m band > with what sounds like composite or phase noise. > > It would seem that, if the transmit composite noise was being bandpass > filtered along with the desired transmit signal, then 20 m should be ~60 > dB down off the passband. We have tried adding a second bandpass to > each with zero change to received noise, and if it was indeed received > noise you would expect it to be reduced even further. > > It is not common-mode currents, several large Mix31 cores with multiple > turns on feedlines did not attenuate it a bit. The rigs are on separate > power supplies and have no galvanic connection to each other, even with > the ground lifted there is no change. > > Any ideas? > > Thanks in advance, > Howie / WA4PSC > > ______________________________________________________________ > 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 > Message delivered to [email protected] ______________________________________________________________ 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 Message delivered to [email protected]
