I have tracked down a lot of man made RFI (mostly from grow light
ballasts) and without exception the signal is vertically polarized until
you get very close to the source. I found this very interesting, so a
friend and I used a battery powered oscillator with an end fed
horizontal wire for an antenna. We placed it horizontally on the floor
of his house on the second floor, the first floor, and finally in the
basement. The signal was always vertically polarized on 40m until we
got very close to the source. I was using a tuned loop antenna for
receive. I had previously determined that the null looking through the
loop indicated vertical polarization, whereas the peak looking through
the loop indicated horizontal polarization. I initially thought this
was caused by the source and antenna being so low to the ground on 40m.
Most of the radiation is going straight up, but EZNEC does not show a
big difference between the vertical and horizontal polarization. I
thought this phenomenon might be caused by the direction of the house
wiring, but that is pretty random, and the oscillator test definitely
had a horizontal antenna that produced predominately vertical
radiation. Any thoughts?
Tom W0IVJ
On 5/21/2017 8:02 PM, Manfred Mornhinweg wrote:
Ron, and all,
I learned: Natural noise (lightning) is vertically polarized because
lightning is a vertical event.
I have seen lots of horizontal lightning, from cloud to cloud, or inside
the same cloud.
Even when I have seen vertical lightning to ground, it has usually
happened simultaneously with horizontal lightning, that brings the
charges to the spot in the cloud where the vertical part starts.
Of course even horizontal lightning noise will arrive at one's place
polarized horizontally, vertically, or anything in between, depending
on the direction of the lightning relative to the direction between
one's place and the lightning. Horizontal lightning aligned with your
path to the lightning generates vertical polarization at your place.
Just like a horizontal dipole antenna operates with vertical
polarization at the directions the wires point.
And then again, any far-away lightning that you hear through
ionospheric propagation will anyway have its polarization thoroughly
mixed up.
Man made noise, like noise motor is generally polarized with it's
> feed wiring.
Yes. And that's typically more horizontal than vertical, because power
lines strung horizontally from pole to pole and pole to houses do much
of the radiating. But some vertical power wires exist - just think
about tall buildings - and of course the noise radiated by a
horizontal power line running straight away from your place appears
vertically polarized.
In short, I don't think there is much merit to the idea that noise is
most commonly vertically polarized. Neither manmade nor natural noise.
The real reason why vertically polarized antennas acquired a
reputation for being noisy is that many such vertically polarized
antennas are simple monopoles fed against ground. This places them at
ground level, where there is most manmade noise. Also most hams run
such antennas without a common mode choke, thinking that the
unbalanced antenna nicely matches the unbalanced coax cable. So if the
grounding is anything but perfect, the feedline becomes part of the
antenna system, and that feedline runs into the house and right past
switching power supplies, CFLs, power wiring, etc. Put the same
vertical antenna high up on a tower, using an artificial groundplane
up there, with a proper common-mode choke on the feedline, and it will
be as quiet as a horizontal antenna installed at the same place.
Most people can easily do this test using a VHF antenna: Place it
vertically or horizontally, at the same height, and compare. Noise
stays the same. I used switchable polarity Yagis on VHF and UHF for
many years, operating on satellites. I could switch to vertical,
horizontal, left hand circular and right hand circular polarizations.
There was no general noise advantage in either of them. Just the
signals, and specific individual noise sources, got stronger or
weaker, depending on the polarization they had.
On UHF I didn't have much manmade noise, but on VHF I did.
Manfred
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