[RFI] Home RFI Hunting

[Jim Brown]

GM Dave,

There are many elements to your problem, one of which may be your choice 
of antennas. I'll begin with this. SWR IS NOT A MEASURE OF ANTENNA 
PERFORMANCE!  What matters are the EFFICIENCY of the antenna for 
transmitting, the directional pattern in three dimensions, the ability 
to HEAR other stations, and match between the rig and antenna so that it 
accepts power.  SWR, as measured in the shack, describes ONLY the last 
of those factors.  The company selling the antenna you have selected 
says NOT A WORD about anything but SWR, and I saw nothing on their 
website telling me anything about any matching network built into their 
"black box." FWIW, $185 is a lot to spend on 130 ft of wire and a magic 
box, which I would guess is most likely a transformer wound on some form 
of ferrite or powdered iron core.  $41 will get me 500 ft of wire, a 
suitable core costs less than $10.

Second: Sadly, it is quite common for we hams to be surrounded by noise 
sources, some of which are under our control and some of which are not. 
Those noise sources in your living room ARE under your control, and you 
should address them first. Study
http://k9yc.com/KillingReceiveNoise.pdf in text form, and
http://k9yc.com/KillingRXNoiseVisalia.pdf as slides for a talk at 
Visalia a year or two ago.

Third, I strongly suggest that you STUDY and IMPLEMENT proper BONDING in 
your home and station as described in my tutorial slide show on the 
topic, and as described in N0AX's ARRL book on Grounding and Bonding.

Fourth, do you plan to operate (or listen seriously) on the new 630m 
band or on the AM broadcast band? ONLY if the answer is Yes should you 
choke noise sources in that frequency range.  While many (most?) noise 
sources are broadband (that is, extending from very low to very high 
frequencies), we only need to choke them in the frequency range(s) where 
we want to hear weak signals.

Fifth, the smartest hams who seriously want to operate or listen on 
bands below 30m use some form of receiving loop antenna to minimize 
noise. And this is AFTER they have put in serious effort to kill as many 
noise sources as possible.

As to your question about multiple chokes -- Dave has given you the 
right answer, but unless you want to seriously listen below 160M,  
Fair-Rite #31 material is the only good choice.

I also suggest that you check the wiring of all the AC outlets in your 
home, especially those to which anything is plugged in. Outlets are 
wired by human beings, and we, as a species screw up now and then. There 
are inexpensive outlet testers that will expose most wiring errors. A 
decent AC voltmeter will also do the job, but takes longer. I found two 
mis-wired outlets in the home I bought in W6 twelve years ago, and 
MULTIPLE serious errors in grounding and bonding of the AC power system 
that caused my house wiring to radiate noise coupled from the outside 
power line!

The most serious issue was that the "ground" wire for the AC power, 
telephone, and CATV went to a water hose faucet 40 ft from the power 
entry, AND that faucet was fed by PVC pipe!  The result was that the 
only ground in my home was the rod driven for my ham station, which is 
in the separate garage-apartment where my ham station is set up. In 
addition to being illegal and unsafe, this wiring error caused noise 
from outside power lines to go to ground through my ham station, which 
made the ham bands VERY noisy!

73, Jim K9YC

On 9/30/2018 8:31 AM, Dave Van Wallaghen wrote:
> 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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>
>
>