[SCCC] RF Noise

[Wolf Leverich, WA6I]

Hi Wyatt -

Several comments:

Ferrite toroids are your friend.  I buy them in $100 lots from Kreger
Components -- usually Mix 31 1.5"ID/2.5"OD toroids, Fair-rite 2631803802.

Note that choking resistance increases roughly with the square of the
number of turns until you get into capacitive bleed and resonance issues,
so you really, really want multiple turns if at all possible.

At least to a point.

8-13 turns will put a real dent in any common-mode hash on a pair of
wires.  (Don't do more than 13T, unless you want to sacrifice choking
on the higher end of the HF spectrum for more on the lower -- and even
then, you might want to use a different ferrite mix if you're a Top Band
contester.)

If you can't get 13T through the toroid, you can use more toroids.  A
famous coax choke is only something like 3 turns through two stacks of
4 toroids.

Wall warts apparently aren't your problem, but you can choke their AC
side by buying a 6' 2-conductor extension cord at Home Depot, winding
it around a toroid, then inserting that between the wall wart and the
outlet.

Besides ferrites, be aware that cables matter.  Some cheap HDMI and
USB cables are pretty efficient noise antennas.  Toroids will help
but a better idea is to buy better cables and then choke them.

Also, Faraday cages can be your friend.  Be aware that a Faraday cage
needs to have walls (rule of thumb) 20x the skin depth of the signal
you want to block, so aluminum foil isn't effective at HF.  But cookie
sheets and even disposable turkey pans are.  Also, aluminum window
screening usually is.  If you can box the noise source, that will help.

Another thing that matters is station grounding.  That's a whole
topic unto itself.

BTW, in my experience DX Engineering Maxi-Core® feedline current chokes
DXE-FCC050-H05-B totally rock if you have noise coming in on your feedline.

Be aware that feedline noise ingress, if I understand what's happening
here, really comes in 3 flavors: feedline to your rig, feedline to your
antenna, and feedline leakage in between.  Burying your coax helps
with everything, and choking it at both your rig and antenna helps.

And I apologize for the sorta-random core dump.  It's been a long day
in a really, really long week and my caffeine reserves are totally 
depleted. hihihihi

73 de Wolf WA6I





On Thu, Feb 14, 2019 at 09:00:13PM -0800, Wyatt Law wrote:
> Hello all,
> 
> I was wondering what everyone else uses to cut down on noise. I used to
> have a problem where whenever I did CW, it would turn off the TVs in my
> house and make my PC monitor flicker. That has been fixed for a while with
> ferrite beads. The only issue that I have now is that whenever my dad's PC
> is turned on across the house, it blows out my IC-7300. It makes a ton of
> noise all over the panadapter and significantly raises the noise level.
> When the PC is turned off, the noise is gone. What could be done to stop
> this? I've read online that people wrap their cables in torrids? If so what
> size and where should I get them? I have tired different combinations of
> beads and looping the coax with no change and was wondering if anyone has
> had any success with torrid wrapping?
> 
> Thanks,
> Wyatt
> AI6V
> wyattlaw4 at gmail.com
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