[RFI] 40 M and DirecTV

Jim Brown jim at audiosystemsgroup.com
Thu Apr 9 09:04:39 PDT 2009

Hi Rick,

See suggestions below.


Jim K9YC

On Thu, 9 Apr 2009 07:20:01 -0700 (PDT), rick darwicki wrote:

>Before I climb the roof..............

I wouldn't suspect anything on the roof, other than possible 
rectification creating a UHF spur that is getting into the satellite. 
Pretty unlikely. Symptoms you describe are far more likely to be 
produced in the receiver module that does the decoding. 

>Is there any reason only 40 meters would make my TV picture rotate 
>10-15 degrees as I key up? I.E. some relationship or thing in the LNA?

I would suspect internal circuitry of the decoding box or the TV 

>Tons of ferrite on everything 

I hope this means that you have chokes with something like 6-8 turns on 
a 2.4-inch toroid of #31 or #43 on every cable that hits that decoder 
box, and on every cable that hits the TV. Single turn ferrites are 
meaningless on 40M. 

>but I suspect one of the 40 meter radials from the vertical terminates
>close to the dish and has high RF on the end.

That could be exciting a lack of shielding problem in the decoder box. 
There is high voltage at the end of a resonant radial. Shielding 
problems are very impractical to fix. Try moving the radial. :) But do 
the other stuff first. 

One suggestion. Try reducing your TX power in steps and make note of 
how much you have to reduce it before the problem goes away. This 
should tell you how big your problem is. 6dB problems (1/4 power) are 
pretty easy to solve. 20 dB problems (1:100 power) are tougher.  


Jim K9YC

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