Hi Russ, the same problem was here with BC station abt 5km away. Only with KPA in the chain. What helps - increasing current in diode switch on KPA board - change of R25 to cca 65 Ohm and there are no IMD products as before. Hope this can help in any similar case in very special configuration of local BC station and non resonant ant used for higher bands. (I had IMD problems from 14MHz up, with with LW ant, BC station on 1062kHz)
GL & 73! Lexa, ok1dst ---------- Původní zpráva ---------- Od: Russ Tobolic <eru...@att.net> Komu: Elecraft@mailman.qth.net <Elecraft@mailman.qth.net> Datum: 10. 11. 2014 17:17:51 Předmět: [Elecraft] Fw: Interesting K3 QRM problem "In this recent discussion here on K3 QRM from strong local broadcast stations, W4TV brought up the noise generated in the T/R switching diodes. In doing some experimentation with a bandpass flter in the loop between the RX antenna "out" and "in" on the KXV3A I have discovered something which has baffled me. I have a 2KW station on 1480 kc 1.5 miles north of me and a 20KW station on 1300 kc about 5 miles south of me. The 1300 station is directional north and I am right in the boresight. I am experiencing +30 to +40 dB over S9 intermod from these two stations on 1840 kc. An intermod calculator shows a 5th order intermod at 1840 from the two stations. I normally run QRP at 5W cw and what I have discovered is that when I crank up the power above 15W (activating the KPA3), the intermod drops to about +5 to +10 dB over S9. This behavior is very consistent when switching between low and high power. Can anyone explain this or is something broke in my K3? Thanks, Russ, N3CO On Thursday, October 23, 2014 4:52 PM, "Joe Subich, W4TV" <li...@subich.com> wrote: > Maybe, and if you're right, my suggestion may not help. But you > misunderstood my suggestion. There is an insert point between the > T/R switch and the RX input. That's the RX loop I was talking about > -- you insert the filter there. The insert point is *after* the PIN diode T/R switches for both the HPA (KPA3) and 10W LPA. Given Vic's description, it is likely the noise is being generated in one or more of the PIN diodes in the T/R switching and placing the highpass filter in the insert point will not resolve the noise. Vic, you can bypass (disable) the KPA3 to see if the noise generation is in the KPA3 T/R switch. 73, ... Joe, W4TV ______________________________________________________________ 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 Message delivered to alexandr.kobra...@seznam.cz" ______________________________________________________________ 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 Message delivered to arch...@mail-archive.com
