The surface wave is what AM broadcast stations depend on for propagation of
their signal. Vertically polarized signals at low frequencies, up to around
4 MHz, will follow the surface well beyond line of sight.
The old 2 MHz marine band also depended on this mode of propagation for
communications on these frequencies. It is a very reliable propagation mode
day or night and you must use vertical polarization.
A horizontally polarized wave will only travel a short distance as it gets
shorted out by the currents it induces in the earth's surface. (See Terman
for references)
I don't remember what the distance is before most of the horizontal
component is gone but I don't think it is too many wavelengths.
73
Gary K4FMX
> -----Original Message-----
> From: towertalk-bounces@contesting.com [mailto:towertalk-
> bounces@contesting.com] On Behalf Of Joe Giacobello
> Sent: Sunday, November 12, 2006 11:20 AM
> To: Jim Jarvis
> Cc: towertalk@contesting.com
> Subject: Re: [TowerTalk] vertical vs horizontal--a different take
>
> Jim, this subject came up in another context several weeks ago. Someone
> said that the horizontal component of the noise signal seems to be
> attenuated much more (by the ground?) than the vertical component. I
> don't believe any explanation was given for the difference, if my memory
> serves.
>
> When I had a 40M vertical with four elevated radials and a 40M EDZ,
> there was no doubt that the vertical was much noisier than the EDZ. Of
> course, the vertical is omni directional while the zepp was
> bidirectional. Nevertheless, the difference was dramatic even at a
> relatively electrically quiet QTH.
>
> 73, Joe
> K2XX
>
>
>
> Jim Jarvis wrote:
> > K8RI's post on this topic finally prompted me to raise a
> > question that's been bothering me for some time.
> >
> >
> > Why is powerline noise vertically polarized? Power lines are
> > horizontal. Yes, it's true that there are vertical runs to
> > ground, every few poles. But why is the noise assumed to be
> > vertically polarized?
> >
> > Is it because that noise seems louder on our vertical antennas?
> > Our UNBALANCED vertical antennas? If you read w1his's white paper
> > on common mode chokes (yccc.com), you'll find that he's reduced the
> > received noise levels substantially by decoupling the feedline.
> > Perhaps I should have said our POORLY DECOUPLED UNBALANCED vertical
> > antennas?
> >
> > George Henf, who founded GAP antennas, maintained that power line noise
> > was horizontal, for the most part....and that his off center fed
> verticals
> > were quieter than a dipole. I didn't challenge him, but the voyager and
> > challenger models I put up to write his manuals, were no noisier than
> > my 40m dipole @ 50'.
> >
> > I've pretty much accepted the common wisdom that manmade noise tended to
> > be vertically polarized, since I became involved with ham radio in 1959.
> > And in the ensuing years, I've heard the 'wisdom' often repeated...but
> > never seen any studies supporting the belief.
> >
> > Anyone care to wade in?
> >
> > n2ea
> >
> > _______________________________________________
> >
> >
> >
> > _______________________________________________
> > TowerTalk mailing list
> > TowerTalk@contesting.com
> > http://lists.contesting.com/mailman/listinfo/towertalk
> >
> >
> >
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|