I am beginning to become crossed up.
How would one Tx both at the same time?
What is a dipole? Horizontally polarized if the dipole is horizontal to the
earth. If it
is vertical to the earth then it is vertically polarized. Now if I take either
dipole and move one of the side so that it is at right angles to the other, ie
horizontal one has one side drop so that it is vertical or the vertical antenna
one side so that it is horizontal, does that make the Tx wave both horizontal
If so why use two separate antennas, and what is an ordinary ground plane
Just donot understand.
Chris opr VE7HCB
Date sent: Fri, 21 Nov 2003 08:56:49 -0800
To: Martin Ewing AA6E <firstname.lastname@example.org>,
From: Jim Lux <email@example.com>
Subject: Re: [TowerTalk] Re: Horizontal + Vertical Polarization
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At 09:39 AM 11/21/2003 -0500, Martin Ewing AA6E wrote:
>Has anyone experimented with feeding both a horizontally polarized
>and vertically polarized antenna simultaneously on HF? Such as,
>feeding a horizontally polarized yagi and a vertical on 20, 15, or
>10 meters? ------
>Well, in my time, we called this circular polarization. That's what
>you have if you feed H and V 90 degrees out of phase, anyway, and if
>the phase centers of the two antennas coincide. If the antennas are
>not symmetric, you'll get elliptical polarization, i.e., circular
>plus linear. If the antennas are physically offset, you'll get
>"interesting" interference fringes on top of the normal radiation
>Circular polarized antennas are insensitive to the (linear)
>polarization angle of the incoming wave, so that eliminates one
>source of QSB. (Propagation can twist the polarization angle, but
>typical HF propagation favors H polarization. It's the same reason
>your Polaroid sunglasses work.) On the other hand, a right-hand
>circular antenna rejects left-hand circular waves, so if both sides
>are playing this game, you'd better agree which sense to use. The
>optimum antenna (on receive, but same argument for transmit) for a
>linearly polarized wave is linearly polarized at the same
>orientation. If you use circular receive for a linear transmit, you
>are going to be down 3 db against an optimum linear antenna. So
>there's no free lunch.
I think, though, that given the random polarization of the incident
wave when it actually hits the antenna(especially given all the stuff
around the typical ham antenna.. relatively few of us have antennas on
tall non-conductive towers, fed with optical fiber, over perfectly
flat salt water marshes, etc.), the fact that most CP (or, more
properly elliptical polarized) antennas have no deep nulls when
receiving a LP signal is significant. Sure, you lose 3dB on the peaks,
but you also don't get the 20-30 dB fade when the signal happens to be
cross polarized. (one reason why TV stations broadcast CP/EP.. it
keeps multipath fades from being so deep)
It would be very interesting(!) if someone were to actually measure
the incident polarization of typical skywave signals (actually,
someone probably has.. the radio astronomy folks working at HF have to
deal with nulling out interferers, etc., and I'm sure some one in the
SW broadcast business has looked at this), particularly in terms of
the short time statistics.
If someone could suggest a simple way to do it, I might do it
myself. Perhaps a couple of short dipoles, fed through a FET switch,
to a receiver like the PCR1000 hooked up to a PC for data logging?
Flip the switch 10 or 100 times a second, etc. I could even look at
the NCDXF beacons or, perhaps something like WWV/WWVH. Shortwave
broadcast might be a good source of a transmitted signal at a known
frequency and time.
See: http://www.mscomputer.com for "Self Supporting Towers",
"Wireless Weather Stations", and lot's more. Call Toll Free,
1-800-333-9041 with any questions and ask for Sherman, W2FLA.
TowerTalk mailing list
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
TowerTalk mailing list