Someone asked me about Polarization Shift on 6m. Who was that? I have a lot
of data I've derived over 50 years. It occurs on all bands in different ways
and lengths of time. A lot of QSB is from Polarization Shift and the only
way you can detect it is by having another antenna of the opposite
polarization(s) to switch to or another beam of the same polarization way in
front of it I'm told. I have a beam that 6 polarization's can be selected of
"Hor, Vert, 45 Left/Right,Circular CW/CCW" with 1:1 SWR instantly selected
from the shack. It's been adapted to a quad DE. It has another advantage.
In pile ups certain signals can be attenuated making others more readable.
It also gives different angles of radiation for additional coverage. Another
useful tool is a beam that can be switched from max gain on transmit and max
F/B on receive. This is a great aid in pile ups.
A beam tuned for max gain will not have max F/B and therefore tends to clear
the frequency on transmit on the back which often improves F/B dramatically.
All this during a contest can make a fair difference.
Using the Backscatter Technique developed at Stanford by Oswald Vlllard in
the late 40's and it's really "Ham Radio Radar." You can instantly see in
time/miles on a scope where your 1st and 2nd hops (even the 3rd) come down
for any antenna or polarization. This is mandatory tool for the DXer in
particular in a contest and for the antenna tester.
There is one problem with polariations other than horizontal. It couples to
a vertical tower progressively as it is or approaches vertical polarization
like 45 degree. It also upsets the beam Z some. Vertical polarization is up
set the most as it swamps the tower and raises the free space lobe or pattern
off the horizon, lowers F/B and can widen the E plane. This affect can
virtually be eliminated by mounting the entire beam (with high F/B) on one
side of the tower with another beam on the other end of the boom pointing the
other way to balance the weight on the boom and tower. Unless this is done
any beam experiments with other polarization's is of limited value. I can
say there is often great value of other polarization's than horizontal as
I've been able to eliminate the tower interference problem.
I hope this answers the question at least partially of who asked about it?
Using different polarization's without tower interference for different
angles of radiation, reducing QSB caused by Polarization Shift and
BackScatter (Ham Radio Radar) are just other areas of communications
improvement not widely used.
I found mounting 2 vertically polarized beams on a horizontal boom equally
spaced on each side of a tower is not as "RF Clean" as everyone thought. The
worst case is 2-2 element vertical beams spaced 1/2 wave apart. That is
about the optimum spacing for 2 element beams and they are also fairly close
to the tower with fat horizontal H Plain patterns. I found that a Plumbers
Delight construction in particular the DE swamps and excites the connecting
boom also as well as the tower to a fair degree. As the gain is increased of
each beam the spacing needs to be wider which gets away from a resonant boom
and the beams are further away from the tower with sharper H Plains. The DE
is further away from the main horizontal boom also. Insulating the DE (and
other elements) from it's boom also helps. Fiberglass booms are practical
for the higher frequency beams like 6m and up. With even higher gain beams
as the spacing needs to be increased, it can approach 1 WL and the same
problems again. A horizontal and beam boom distance to the DE's of 3/4 WL
has been shown to reduce the coupling to it. I ran a bunch of patterns in
Eznec and the "hot boom" problem was very clear.
I used 2 of the old Workshop 3 element 10m beams vertically polarized about
20' apart 35' high with directly fed and floating 50 ohm feedpoints about 45
years ago with great success. I had a 3 element horizontal 10m beam about
20' higher for a reference beam and could run them together in various ways
for different polarization combinations. I literally owned the frequency
28.503 MHz in the AM days. I will duplicate this in Eznec, see what the mast
and boom lighting was and perhaps it can be improved or I lucked out with the
configuration I had. The 3 element beams only had 5.5 dB gain each or say
8.5 dB stacked vertically polarized. It had a potentially low angle of
radiation and somewhat unexplained performance. So I will do it over and see
if it still has it's original "RF Clout" on 10M. I had a "HAI Problem" a
block away the first day. I got into a guys Hearing Aid. The first contact
I made was while loading it up. Some guy comes back and comments about the
carrier. We go back and forth a few times and I finally mention my call. He
said "he was surprised as my carrier was so steady he first thought it was a
local signal and that was why he didn't mention his call." It was a LU in
Buenos Aries. I knew this was going to be an exciting beam.
The low QSB characteristic was typical of many contacts. One explanation for
it is the vertical beams E Plain is sharper than the H Plain which is
normally the vertical pattern of horizontal beams. A sharper vertical
pattern has the affect of reducing the strength of the secondary lobes which
can cause QSB. Stacked beams sharper vertical pattern tend to do the same.
Just rotating the beam 90 degrees can sharpen the vertical pattern about 20
degrees on a side. You would have to increase the gain of beam at least 3 or
more dB to do the same (boom twice and long and/or longer). Even back then I
could see that I could get a lot of sharpening of the vertical pattern just
by rotating the beam 90 degrees but at the same gain (3 dB more with 2),
different ground losses and different angles--perhaps a lower one than when
horizontal. I hoped this was the "Magic Bullet" of improvement that was
certainly worth the try. I still have a picture of it. The 2 vertical beams
usually had the signal and lack of QSB edge over the top horizontal beam more
than the gain difference for the band conditions of the time. 6m operators
have claimed great success with 2 vertically polarized beams but didn't have
a reference horizontal beam. I will be testing this again next spring on 6m.
It appears to me that very effective performance is possible with 2
vertically polarized beams lower to the ground based on my results if the
supporting booms and mast are RF clean. K7GCO
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