[RFI] Fwd: Re: Home RFI Hunting

[Dave Van Wallaghen]

--- Forwarded message ---
From: Dave Van Wallaghen <dave at w8fgu.com>
Date: September 13, 2018 15:40:17
Subject: Re: [RFI] Home RFI Hunting
To: wa2lbi at gmail.com

> Thanks for the reply Ken.
>
> I did isolate the TV by doing what you suggest and indeed it is the SMPS in 
> the TV (the TV does not even need to be on - just plugged in). I do have 
> some problems with the wall warts for the cable box and a DVD player and 
> looking to replace them. But with just the TV plugged in on that circuit 
> the noise is present.
>
> Thanks again for the suggestions.
>
> 73,
> Dave W8FGU
>
>
>
> On September 13, 2018 14:42:56 "wa2lbi at gmail.com" <wa2lbi at gmail.com> wrote:
>
>> 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
>>
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