Broadcast Intermod (?)

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Rob K2CU:
If you think it is your receiver, first see if it shows up on another radio.  My 51J-4, which is similar to the R-390, easily overloads on strong local signals. Try putting a 10 dB pad on the input and see if the signals go down 10 dB or disappear. IF the intermod is being generated externally first verify that your own house is not responsible...i.e. gutters, guy wires, towers, etc. You could try and retune a small transistor AM radio to cover the 160 meter band., then use it as a sniffer.

If the intermod is coming from far away, are there any other guys in your area to help try and locate it? The little AM radio sniffer's loopstick antenna is pretty directional (a null) and you might be able to get bearings from it.

K3ZS:
Worst case I experienced was when I was involved with the local club's 2M repeater activities.    A nearby installation was creating a signal on the input frequency of the repeater intermodulating with the repeater's transmitter signal.    This was proved with directional antennas and a spectrum analyzer.   We couldn't convince the other operator to do anything about it.   The club gave up and moved the repeater somewhere else.

k4kyv:
I sometimes hear what sounds like FM broadcast on the HF bands.  I can just barely understand the audio at times and at other times just tell that it is speech or music.  The deviation seems much wider that the  bandwidth of my receiver, even at 16 kHz.  I seem to hear it most often on 40m, but I have heard it on 75/80 and maybe IIRC a time or two on 160.  At times it is very strong, and I pick the same thing up on multiple receivers.  I suppose it could be the same kind of intermod taking place between FM stations.  For example, 90.3 and 94.1 could leave a difference product at 3800 kHz.

AF9J:
Quote from: Rob K2CU on February 24, 2008, 11:28:22 AM

If you think it is your receiver, first see if it shows up on another radio.  My 51J-4, which is similar to the R-390, easily overloads on strong local signals. Try putting a 10 dB pad on the input and see if the signals go down 10 dB or disappear. IF the intermod is being generated externally first verify that your own house is not responsible...i.e. gutters, guy wires, towers, etc. You could try and retune a small transistor AM radio to cover the 160 meter band., then use it as a sniffer.

If the intermod is coming from far away, are there any other guys in your area to help try and locate it? The little AM radio sniffer's loopstick antenna is pretty directional (a null) and you might be able to get bearings from it.



Hi Rob,

All of my receivers suffer from intermod to a greater or lesser extent.  My FT-897D had problems with it (when I owned it).  My TS-820 also suffers on 75m (but hardly at all on 160).  The most intermod resistant receiver I have is in my IC-740, which only picks it up in a few spots on 75m. The worst is my SX-96.  There are a couple of spots on 160, and a whole bunch from about 3630 to about 3840 or 50 (it's hard to tell on the SX-96 bandspread dial - it isn't very frequency accurate) on 75m, that I have to deal with BCI intermod, on my SX-96.

73,
Ellen - AF9J

Ed/KB1HYS:
Yep, I hear it on two different receivers.  When both are in the shack.  Seems worse in the daytime. I do hear more than one set of intermodulated stations.  Very clear, like listening to two radio's at the same time. I will have to start looking around for a possible source I guess.  This should be fun...  ::)

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