[RFI] Fwd: Re: Home RFI Hunting

[Dave Van Wallaghen]

My apologies to the list. I only replied to the sender and not the list.

--- Forwarded message ---
From: Dave Van Wallaghen <dave at w8fgu.com>
Date: September 13, 2018 15:34:56
Subject: Re: [RFI] Home RFI Hunting
To: jim at audiosystemsgroup.com

> Thanks for the reply JIm. I doubt you would remember, but we met once in 
> Dayton a few years ago. I've been working in the Elecraft booth for the 
> last 10 years or so.
>
> On September 13, 2018 14:23:44 Jim Brown <jim at audiosystemsgroup.com> wrote:
>
>> 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.
>
> I will certainly try this. Do you think rewiring the panel to place my 
> shack circuit on the opposite phase from the AV circuit might help as well?
>
>>
>> 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.
>
> Although I don't have decent antennas for 630m, I would like listen in and 
> this noise will prohibit that. I was able to hear airport beacons over 100 
> mi away when I unplugged the TV.
>
>>
>> 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 did. The only other cable is an HDMI connection and I was able to get 13 
> turns around a #31 core. I did this close to the TV but maybe I should 
> place one near the cable box as well.
>
>>
>> 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 kind of thought as much - makes sense. Just thought I would ask.
>
>>
>> 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.
>
> Yes, I was surprised as well since I bought this to replace a satan 
> worshiping plasma TV ;-)
>
> It does appear to be the PS for the TV (it generates this noise even when 
> turned off - just plugged in) and the supply is internal to the set. I did 
> unplug the other wall warts on the circuit - the cable box and a DVD 
> player. I do have some issues with those as well and looking for 
> replacements. I measured the outputs of each and they are right at 12v. So, 
> I think they are regulated. But, the noise is very prominent with just the 
> TV plugged in on that circuit.
>
> Thanks again for the reply and I will first try the separate grounds to see 
> if I can reduce it some.
>
> Take care,
> Dave W8FGU
>
>
>>