[TowerTalk] [Spam] TowerTalk Digest, Vol 73, Issue 24

[Bill Fuqua]

    I just looked at the RatPak users guide, no schematic but looking at 
the PCB there are
protective diodes across the relay coils.  Also it uses a multi-conductor 
cable.
It is possible the multi-conductor cable is the antenna picking up the AM 
broadcast signals
and the diodes do the mixing and the cable re-radiates the resulting 
by-products to your
antennas. You may find the problem goes away if you both bypass the box 
and  temporarily
disconnect the cables at the switch box. If this is the case the solution 
would be to replace the
diodes with a RC snuber circuit. Or increasing the capacitance across the 
diodes.

73
Bill wa4lav




At 09:23 PM 1/8/2009 -0500, you wrote:
>The intermodulation takes the form of (2x Frequency 1) + frequency 2. I
>have no less than 6 strong AM stations that all interact with each other
>to basically wipe out most of 80m. The intermod products vary from S9 to
>S9+20dB.
>
>I have installed a high pass filter in line that reduced the
>fundamentals at least 40 dB but the intermod remained unchanged. Added a
>30 dB pad on the input, no change in intermod except being reduced by 30
>dB.
>
>I have a single feedline (7/8" Heliax) with a jumper to the radio
>connected to a RATPAK tower mounted switch. Switching between multiple
>antennas yields intermod with slightly varying levels. When selecting an
>open connector port, Intermod drops to almost nil but is just slightly
>detectable.