[RFI] Home RFI Hunting

[wa2lbi at gmail.com]

I haven't heard much noise from LCD TVs or monitors.  You could disconnect all cables to the TV except power and put a 75 ohm terminator on the coax connector.  Power up the TV and listen for noise.  If none, connect the antenna and check for noise.  Continue connecting cables until noise appears and try to fix each before moving to the next until all cables are connected.  
Ken WA2LBI LG G6 

------ Original message------From: Jim BrownDate: Thu, Sep 13, 2018 14:23To: rfi at contesting.com;Cc: Subject:Re: [RFI] Home RFI Hunting
On 9/13/2018 10:36 AM, Dave Van Wallaghen wrote:
> So, my questions are: as the largest portion of this noise comes from 
> my TV plugged into the AV circuit, would running separate grounds for 
> my AV and shack circuits back to the panel help alleviate some of the 
> noise that I find on my shack circuit ground? Or do you think most of 
> it is being physically coupled? I would have tried this myself, but 
> while certainly doable, it will be a little work to make it happen.


Several thoughts on this.

First, RF noise from defective/poorly designed equipment OFTEN travels 
on the green wire, so yes, separate green wires is a good thing.

Second, chokes to kill noise currents need to be tuned to the 
frequency(ies) where you are bothered by the interference. While PROBING 
for noise sources at lower frequencies can be effective, there's no need 
to choke those frequencies unless you use your radio there.

Third, if the TV is a noise source, I would choke every cable connected 
to it, starting with those that are likely to be the most effective 
radiators, first the power cable and coax feeding it, then audio and 
video cables if there are any.

>
> I also read on the Polamar website about using #75 mix Clamp On cores 
> for use on frequency ranges down to 200 kHz. Is this something 
> applicable to my problem? 

Only if you need to kill noise on the new 630M band, and only if you 
wind a lot of turns. Simply clamping one or more of them onto cables is 
unlikely to do much.

I'm surprised that you're hearing a lot of noise coming from an LCD TV. 
The most likely source would be a poorly filtered switch-mode power 
supply built into it. I would also look for other sources around the TV, 
like switch-mode wall warts for various equipment, or built into other 
equipment.

73, Jim K9YC