[RFI] Power Line Noise

Jim Brown jim at audiosystemsgroup.com
Thu Apr 16 23:30:50 EDT 2020

On 4/16/2020 2:32 PM, K9MA wrote:
> The current from an arcing device like a lightning arrestor flows in 
> BOTH directions away from the source on the horizontal lines, so the 
> horizontal component largely cancels out. It's like the top of a "T" 
> antenna.

I'd buy that if the wires were close together, but NOT at the wide 
spacing typical of HV lines. Think about it -- twisted pair is FAR 
better (20-30dB) than "zip cord" at rejecting all forms of crosstalk and 
coupling, simply because interfering fields are close to one conductor 
than the other. That's a fairly small differential, but the two 
conductors in the AC distro system have far greater spacing. They're 
also typically 3-phase.

> The radiation then mostly comes from the vertical ground wire.

I'm good with this (and I've seen it), but for a different reason -- it 
can be carrying the arcing of both conductors, perhaps from GFCIs?
> Generally, I've found the HF beam heading to be pretty accurate for more 
> distant sources, perhaps because the vertical component is attenuated 
> more quickly.

I agree with Mike that antenna arrays develop their directivity in the 
far field, and can be VERY different in the near field. Polarization of 
the RX antenna might be part of it.

  With the VHF tracker (135 MHz), I do find I have to
> sometimes turn it vertically, but not consistently up close. I expect 
> the shorter wavelength has something to do with that.
> In any case, the moral of the story is don't just look in the direction 
> your HF beam thinks it's coming from!

I'm not suggesting that anyone in this thread might be making this 
mistake, BUT -- remember that antenna arrays are all based on spacing, 
phase relationships, and spatial relationships between elements as 
ELECTRICAL length. A tri-bander only exhibits it's design directivity on 
those three bands. Its directivity on any other band, including 2M, 
should be thought of as "random," like the infinite number of monkeys 
and typewriters. :)

73, Jim K9YC

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