[RFI] Home RFI Hunting

[Dave Van Wallaghen]

First, thanks to all of you who replied on the list and privately. I 
appreciate all the advise.

I just wanted to follow up on this as I tried a few things and I sheepishly 
bring the solution to my buzzing noise problem on the low end of the AM 
band and 600m in case anyone else runs into my situation.

I did run a separate AC ground back to the panel physically separating my 
shack circuit from my problematic AV/TV circuit. This had no effect what so 
ever. So while pondering why this noise is so prominent if my antenna or 
rig is connected to the AC ground system, my inexperience waned enough that 
I finally figured out what was going on. In my first email, I failed to 
mention that the antenna I was using is a 80-10m multi-band end fed from 
MyAntennas. This seemed like a logical choice since it is resonant on all 
of the ham bands I wanted to test and does fairly well on 160m and 600m as 
well.

So yes, the coax shield of the feedline of the antenna acts as the 
counterpoise for this antenna, and in effect, everytime I connected the AC 
ground to the rig or antenna ground, it was coupling the noise directly to 
my antenna system and rig. Several turns of the feedline through a #31 core 
at the rig end greatly reduces the buzzing. It reduced the noise for S9+5 
to a respectful S5-6 which is what I was seeing when I floated the ground 
of the rig and antenna. I still have a little noise between 380-480Khz that 
I will tweak and see if I can eliminate all together.

This leads to my next question: I was thinking of using a #77 mix core in 
series with the #31 to help here as the #77 has a higher impedance in the 
lower frequencies. I may have missed it in Jim, K9YC's RFI pdf, but does 
series mean the two cores together with the cable passing through them 
simultaneously? Or two separately wound cores? I apologize if this is a 
dumb question. I've learned a great deal throughout this process and I 
might just be a little overloaded at the moment ;-)

73,
Dave W8FGU




On September 13, 2018 14:23:44 Jim Brown <jim at audiosystemsgroup.com> wrote:

> 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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