Topband: 9 kHz heterodyne BCI

[Lee K7TJR]

Greetings Bob,  Having BC intermod on 160 meters has been a problem for a many years.
 It generally occurs from 2 or more of your 9KHz spaced BC signals mixing together and coming out on their spacings on 160 Meters.
  Mixing is the key word here and will be the key if you find the source.
   Mixing can occur right at the BC transmitter location from other signals coming back down the BC station antenna and mixing in their power amp.
   Mixing can occur in many different places between you and the BC stations. This can occur where there are fairly long conductors joined with a lousy rusted or corroded connections.
   This can be a line of fencing or guy wires on a power pole or many many other places where two things come together with a less than perfect connection.
    Mixing can occur in your own antenna if there are any bad connections or unwanted things touching the antenna. It can occur in a tower with bad joint connections.
    Mixing can occur in your feedline if you have bad splices or bad connector installation.
    Mixing can occur in a Preamp commonly used with receiving antennas. Disconnect it to see what happens.
    And mixing can occur in your own radio if BC signals are quite large.
You were using a K3 so I suspect the mixing may not be in your radio.
You can work back from the radio looking for potential problems.
If you use a preamp you can eliminate it and check the levels of BCI left. If the bci is caused by the preamp the BCI should be reduced by more dB than the gain was reduced.
   Look around to see if there are any potential items such as a rain gutter or wire fence near your RX antenna
 Sometimes a portable radio can help locate the source if it is local by sniffing around any metal items in the area.
 Perhaps you could use a mobile radio to expand your range.
  Check to see how close your radio stations are to your antenna farm. Really close can easily mean overload of your system.
  Use a BC radio connected to your RX antenna and try to get some idea of the strength of the BC stations so you know what you are working with.
 Good luck, sometimes this is very difficult to find.

Lee   K7TJR 


Hi we just got QRV on 160 right before the SP and noticed AM BCI at 1800 kHz and every 9 kHZ  up from there. Since 9 kHz is the BC channel spacing here I suspect two adjacent stations are mixing. Somehow somewhere. Maybe here in my station, one of the BC stations or somewhere else?
Unfortunately our new HiZ 4/8 array was rendered inop before we could finish it due to rodents chewing away sections of the feedlines. We rigged up 2 2-way one wave Beverages and these heterodynes were the same strength from all 4 directions on them. Opening our tx vertical had no effect.
Anyone know the likely cause/cure for these observations?
TIA 73 Bob HS0ZIA
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