[RFI] Inter-station interference question.

Jim Brown jim at audiosystemsgroup.com
Thu Nov 21 12:49:14 EST 2019

On 11/21/2019 3:00 AM, Martin Sole wrote:
> Dear Jim and Mike,
> Thanks very much for the prompt replies.
> Jim, I think the chokes are either from your latest work using big 31 
> rings or from the design by GM3SEK using multiple big beads and with I 
> believe at least two such chokes in series. That is for each of the 
> feeds to the antennas. The chokes are placed just slightly before the 
> Array solution balun, again one at each feed point. I will review your 
> other document as well, I can see it references issues similar to that 
> which I have observed first hand. Yes the harmonic DOES have a growl to it!

THAT tells you it is PIM. Stubs and filters can't help with this at all. 
First move suggested to bond around the rotator. If still there, look 
for some other culprit.

> The cable is predominantly 1/2" heliax of various manufacturer, based on 
> what is available in country but all used in pro installations so 
> generally decent stuff. There is some RG214 and some may have a foil. I 
> do know that some of the stubs and their associated coupling cables I 
> prepared are made with an RG214 that has  2 braids plus a foil and a 
> dielectric that has 0.8v.f.
> If foil and braid coax is used what is the issue?
> Is there a PIM risk between the braid and the foil?

I did not raise this issue.

73, Jim K9YC

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