I went through this issue with a ham repeater at a mountain top tower. 
The repeater would key up and never let go as it saw some signal it 
thought was a user. I was in a metal cargo container and the repeater 
was in a frame building 20 feet away.
I could turn off the ethernet switch and the interference would go away.
I could leave the switch powered up and remove all the cat 5 cables to 
it and the interference would go away.
It appears the ethernet switch was mixing several RF sources and 
emitting a sum or difference of the two (or more).
I tried Ferrite rings on all cat 5 cables, shielded cable etc. Nothing 
really worked that well.
Finally I moved 100' away to a different building on a different tower 
and no one is complaining now. Spacial separation seems to have fixed it.

Kurt Fankhauser wrote:
> Has anyone else here ever been co-located on a tower with a HAM radio
> (144-148mhz) VHF repeater or perhaps even a commercial system in the 150mhz
> band and gotten complaints that your Ethernet cable is causing them
> interference on their repeater? We are trying to locate the source of noise
> on an amateur radio repeater system locally and last time I went up on grain
> leg there was a whole lot of Ethernet cabling strung everywhere and I've
> read some links such as these. http://www.hamuniverse.com/linksys.html that
> apparently some brands of equipment give out much more spurious emissions
> than others.
> 
>  
> 
> Also how did you work with the radio people to solve it? Seems to only be
> apparent in the VHF band.
> 
>  
> 
>  
> 
>  
> 
> Kurt Fankhauser
> WAVELINC
> P.O. Box 126
> Bucyrus, OH 44820
> 419-562-6405
> www.wavelinc.com
> 
>  
> 
>  
> 
>  
> 
> 
> 
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