At 11:33 AM 11/4/2006, Rick Karlquist wrote:
>Jim Lux wrote:
> > At 08:05 AM 11/4/2006, Bill Turner wrote:
> >
> >
> > Just curious.. I've heard and read the assertion of "man-made noise
> > being predominantly vertically polarized", but after some casual
> > research, I can't find an original source of the data. Does anyone
> > know the basis of the assertion? Actual measurements? Where? What
> > frequencies? When?
>
>Any inverted vee is a much better receive antenna that any vertical at
>my QTY. So at least at my QTH, it's just a fact. Now if I drive my mobile
>to a place with no power lines, the receive noise during the day
>drops to virtually zero. Hence, the vertical is picking up man
>made noise. I should also note that if I drive the mobile around
>in areas (even rural) with power lines, the noise is always much
>higher than in no power line areas.
I would agree that there's a lot of manmade noise about, it's the
assertion that it's *predominantly vertically polarized* that I'm
curious about.
I would imagine that any antenna raised into the air some distance
might be better than something really close to the ground, if only
because of the null right at the horizon. I would expect that
manmade noise, by and large, is going to be coming in at VERY low
angles (i.e. not skywave propagation). {for instance during a big
wide-area power blackout, is the received noise, say, 1000 km away,
in the direction of the blackout, reduced?)
So maybe it's not so much a polarization of the noise, which,
frankly, I'd expect to be random or horizontal (radiated from power
lines), but that typical amateur antennas of two general classes
(horizontal and vertical) tend to have very different patterns.
I'm sure someone out there has actually measured the polarization
properties of manmade noise (probably in connection with big HF radio
telescopes, like LOFAR).
The FCC OET was doing some sort of study on quantifying interference
and noise, using a "noise brightness temperature" sort of
measure. The traditional interference measures tend to assume narrow
band signals, and when you're looking at hundreds or thousands of
wideband emitters (like 802.11, etc.) it looks more like a rise in
the thermal noise floor.
I would imagine that a mobile rig (with a short antenna) is pretty
random polarization, especially since it's next to a vehicle and
close to the ground.
>Rick N6RK
Jim, W6RMK
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