Mechanically rotating your yagi to change polarization
 

Hi. Has anyone designed a way to mechanically rotate their VHF/UHF yagi so
that it can be either horizontally or vertically polarized? If so, can you
please direct me to a website or whatever. Preference right now for a
manual system, but would also take a look at motorised systems.

TIA.

Rich.

(Followup set to rec.radio.amateur.antenna, so all replies will go to this
group).

Caution:

When rotating a Yagi to vertical polarization, the mast and feedline must be
clear of all the antenna elements, and preferably any conductor in the plane
of the elements is located outside the near field. Otherwise there is no
pattern and forward gain and F/B both suffer, sometimes very badly. This
then leads to some arrangement of 2 antennas on a cross boom which pivots in
the middle. This has been described from time to time in all the ham
magazines and other postings, but I don't have a specific URL. I have done
it with my own design several times until I got enough towers to have both
at the same time.

--
Crazy George
Remove N O and S P A M imbedded in return address
"Richard" wrote in message
...
Hi. Has anyone designed a way to mechanically rotate their VHF/UHF yagi so
that it can be either horizontally or vertically polarized? If so, can
you
please direct me to a website or whatever. Preference right now for a
manual system, but would also take a look at motorised systems.

TIA.

Rich.

(Followup set to rec.radio.amateur.antenna, so all replies will go to this
group).

Many years ago, polarization on 2 meters was a hotly debated subject. For
instance, in New England, horlzontal was the preference but in New Jersey
vertical ruled. Now this was around 1950, well before FM became widely used on
2 meters. So there were several articles in QST and CQ about so-called
"flop-over" arrays. Probably the best known was the pair of 5 element Yagis,
the design for which was worked out by a W2 in Southern New Jersey.
Fast-forwarding by 50 years or so, I would think you could do a similar
thing with a pair of Yagis. It should work out better than a single Yagi,
since the feedline wouldn't be parallel to and in the same plane as the
elements when you're using vertical polarization.
73
Cal K4JSI

"Richard" wrote in message
...
Hi. Has anyone designed a way to mechanically rotate their VHF/UHF yagi so
that it can be either horizontally or vertically polarized? If so, can
you
please direct me to a website or whatever. Preference right now for a
manual system, but would also take a look at motorised systems.

TIA.

Rich.

Do a Google search under 70cM EME. Polarity rotation to avoid Faraday loss
is routine with these arrays- but they are arrays- so the mast/ feedline
plays virtually no roll in pattern- as it assuredly will in a single yagi
when vertically polarized.

Dale W4OP

Many years ago I used a car windscreen wiper motor and gearbox to do
just this. IRRC the boom was monted in two ball races and there was an
operating arm , set at 45 degrees to the main polarisation, which was
attached to the wiper motor and the boom. Sorry but I really can't
remember any further details but ISTR that I had to make the motor
operate in "one wipe" mode by frigging the switch.
hth and seasons wotzits, Mike W, G8NXD
--
On Tue, 23 Dec 2003 10:24:12 -0000, "Richard"
wrote:

Hi. Has anyone designed a way to mechanically rotate their VHF/UHF yagi so
that it can be either horizontally or vertically polarized? If so, can you
please direct me to a website or whatever. Preference right now for a
manual system, but would also take a look at motorised systems.

TIA.

Rich.

(Followup set to rec.radio.amateur.antenna, so all replies will go to this
group).

Richard wrote:
Hi. Has anyone designed a way to mechanically rotate their VHF/UHF yagi so
that it can be either horizontally or vertically polarized? If so, can you
please direct me to a website or whatever. Preference right now for a
manual system, but would also take a look at motorised systems.

VHF/UHF antennas are cheap and small enough so that you can make/buy two
and mount them 90 degree apart and have two separate feeds, if you feel
you absolutely need different polarizations.
Iow, any mechanical rotation would be either more expensive, more
complicated or more time consuming (or all of the above) than simply
installing two antennas.

73 ... WA7AA


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Mike W wrote:
Many years ago I used a car windscreen wiper motor and gearbox to do
just this. IRRC the boom was monted in two ball races and there was an
operating arm , set at 45 degrees to the main polarisation, which was
attached to the wiper motor and the boom. Sorry but I really can't
remember any further details but ISTR that I had to make the motor
operate in "one wipe" mode by frigging the switch.
hth and seasons wotzits, Mike W, G8NXD

Yep, that's an idea.

I could buy 2 yagis, it's not really the expense, but a question of loading
on my scaffolding pole mast! :c)

Or I figure a peice of string and some kind of mechanism.

VHF/UHF antennas are cheap and small enough so that you can make/buy two
and mount them 90 degree apart and have two separate feeds, if you feel
you absolutely need different polarizations.

Double the ice/wind load, and double the weight.
Though the weight might be equal with a rotatable single, with the
mechanism.

Dave VanHorn wrote:

VHF/UHF antennas are cheap and small enough so that you can make/buy two
and mount them 90 degree apart and have two separate feeds, if you feel
you absolutely need different polarizations.

Double the ice/wind load, and double the weight.
Though the weight might be equal with a rotatable single, with the
mechanism.

Ice and wind load are hardly a concern on VHF, unless one is stacking a
moonbounce array.

73 ... WA7AA


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Ice and wind load are hardly a concern on VHF, unless one is stacking a
moonbounce array.

I know a few guys who would like to sell you some antennas that don't have
anything wrong with them, then..