Need advice: 6M beacon antenna at 10K ft
 

I'm starting a project with some other guys on a 6M beacon
which will end up on a mountaintop at around 10K ft in New
Mexico. During winter, that means sub-zero temperatures,
high winds, and ICE build-up on everything exposed. We would
ideally like to put up an omnidirectional horizontally
polarized antenna like a loop. Anyone have experience with
building (or purchasing) such an antenna that would be
sufficiently bulletproof to stand up to a severe weather
environment? We could go vertical, of course, but since this
beacon will be operating in a CW weak-signal environment
under a wide variety of propagation modes (including ground
wave, troposcatter, etc., where polarization is more
important than it is with ionospheric propagation), we'd
like to stay with horizontal if it's physically realistic to
do that. What we don't want to have to do, however, is trek
up to the mountain top every weekend to put the antenna back
up. g

Bill / W5WVO
Albuquerque NM

I'm starting a project with some other guys on a 6M beacon
which will end up on a mountaintop at around 10K ft in New
Mexico. During winter, that means sub-zero temperatures,
high winds, and ICE build-up on everything exposed. We would
ideally like to put up an omnidirectional horizontally
polarized antenna like a loop. Anyone have experience with
building (or purchasing) such an antenna that would be
sufficiently bulletproof to stand up to a severe weather
environment? We could go vertical, of course, but since this
beacon will be operating in a CW weak-signal environment
under a wide variety of propagation modes (including ground
wave, troposcatter, etc., where polarization is more
important than it is with ionospheric propagation), we'd
like to stay with horizontal if it's physically realistic to
do that. What we don't want to have to do, however, is trek
up to the mountain top every weekend to put the antenna back
up. g

Bill / W5WVO
Albuquerque NM




---------------------------
The neat thing about running a loop is you can put some DC through
it in the winter to keep the ice off.
KC*VIF
Greg Z
to thine own sound be true

greg z wrote:
We would
ideally like to put up an omnidirectional horizontally
polarized antenna like a loop.

A vertical 6m loop wouldn't be omnidirectional and a horizontal
6m loop would send most of your power up at a take-off-angle of
60 degrees. How about a vertical folded monopole with a good
ground plane?
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil,

I think by a loop he meant something like a Halo. They seem to be pretty
common with beacons. You could stack two of these vertically for gain, but
at 6m the spacing gets kind of long. My concern would be that the thing
still works when the matching element gets iced over.

Bill: Talk to tyhe people at M Squared.

Tam/WB2TT
"Cecil Moore" wrote in message
...
greg z wrote:
We would
ideally like to put up an omnidirectional horizontally
polarized antenna like a loop.

A vertical 6m loop wouldn't be omnidirectional and a horizontal
6m loop would send most of your power up at a take-off-angle of
60 degrees. How about a vertical folded monopole with a good
ground plane?
--
73, Cecil http://www.qsl.net/w5dxp



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"Bill VanAlstyne" wrote in message ...
I'm starting a project with some other guys on a 6M beacon
which will end up on a mountaintop at around 10K ft in New
Mexico. During winter, that means sub-zero temperatures,
high winds, and ICE build-up on everything exposed. We would
ideally like to put up an omnidirectional horizontally
polarized antenna like a loop. Anyone have experience with
building (or purchasing) such an antenna that would be
sufficiently bulletproof to stand up to a severe weather
environment? We could go vertical, of course, but since this
beacon will be operating in a CW weak-signal environment
under a wide variety of propagation modes (including ground
wave, troposcatter, etc., where polarization is more
important than it is with ionospheric propagation), we'd
like to stay with horizontal if it's physically realistic to
do that. What we don't want to have to do, however, is trek
up to the mountain top every weekend to put the antenna back
up. g

I'd immediately consider a ruggedized Squalo.

http://www.wia.org.au/armag/2002/AR_May02_TA1.pdf

I doubt that the specific design shown in the article would take the
kind of abuse you're talking about but it's a conceptual and
dimensional starting point I'd make the loop from one inch copper
water tube and 90 degree soldered copper elbows. I wouldn't use a
gamma match, they're trouble looking for a place to start in an
application like this. I'd attach a few feet of some kind of good RG-8
size coax directly to the feedpoints and string (suitable) ferrite
beads on the coax right at the feedpoint. Then run the coax down the
antenna support to a sealed box which contains some sort of simple
tuning network which would be completely out of the weather. I'd also
make really sure the loop was well supported including nonconductive
struts from the support mast to the far corners of the loop.

There would be a good bit of cut and try involved, material selection
issues and mechanical details to be worked out but hey, that's ham
radio for ya!


Bill / W5WVO
Albuquerque NM

Brian w3rv


---------------------------
The neat thing about running a loop is you can put some DC through
it in the winter to keep the ice off.

Where are ya gonna get those kinds of amps? As in amperes.

KC*VIF
Greg Z
to thine own sound be true

"greg z" wrote in message
...
I'm starting a project with some other guys on a 6M beacon
which will end up on a mountaintop at around 10K ft in New
Mexico. During winter, that means sub-zero temperatures,
high winds, and ICE build-up on everything exposed. We would
ideally like to put up an omnidirectional horizontally
polarized antenna like a loop. Anyone have experience with
building (or purchasing) such an antenna that would be
sufficiently bulletproof to stand up to a severe weather
environment? We could go vertical, of course, but since this
beacon will be operating in a CW weak-signal environment
under a wide variety of propagation modes (including ground
wave, troposcatter, etc., where polarization is more
important than it is with ionospheric propagation), we'd
like to stay with horizontal if it's physically realistic to
do that. What we don't want to have to do, however, is trek
up to the mountain top every weekend to put the antenna back
up. g

Bill / W5WVO
Albuquerque NM


Omni (quasi) loops for V/U are open at the far end
HF loops (typically 1 wavelength) that are closed loops) have a pattern
almost identical to a dipole- i.e. not even close to omni
Dale W4OP

On Sun, 08 Feb 2004 17:51:32 GMT, "Dale Parfitt"
wrote:


"greg z" wrote in message
...
I'm starting a project with some other guys on a 6M beacon
which will end up on a mountaintop at around 10K ft in New
Mexico. During winter, that means sub-zero temperatures,
high winds, and ICE build-up on everything exposed. We would
ideally like to put up an omnidirectional horizontally
polarized antenna like a loop. Anyone have experience with
building (or purchasing) such an antenna that would be
sufficiently bulletproof to stand up to a severe weather
environment? We could go vertical, of course, but since this
beacon will be operating in a CW weak-signal environment
under a wide variety of propagation modes (including ground
wave, troposcatter, etc., where polarization is more
important than it is with ionospheric propagation), we'd
like to stay with horizontal if it's physically realistic to
do that. What we don't want to have to do, however, is trek
up to the mountain top every weekend to put the antenna back
up. g

Bill / W5WVO
Albuquerque NM


Omni (quasi) loops for V/U are open at the far end
HF loops (typically 1 wavelength) that are closed loops) have a pattern
almost identical to a dipole- i.e. not even close to omni
Dale W4OP


Huh!? According to the article on L. B. Cebik's web page, a
one-wavelength horizontally oriented, horizontally polarized loop
antenna has a nearly circular pattern. As a large loop is driven by
increasing frequencies, the pattern becomes more like a starfish, but
it radiates relatively symmetrically in several directions, the number
of lobes increasing with frequency. A dipole has a broad
figure-of-eight pattern and a pair of strong lobes with minor
lide-lobes as it is driven by increasing frequencies. Try modelling a
dipole and a closed loop and see for yourself, don't believe me.

Russ

Russ wrote:

"Dale Parfitt" wrote:
HF loops (typically 1 wavelength) that are closed loops) have a pattern
almost identical to a dipole- i.e. not even close to omn

Huh!? According to the article on L. B. Cebik's web page, a
one-wavelength horizontally oriented, horizontally polarized loop
antenna has a nearly circular pattern.

Dale is obviously talking about a vertically oriented loop. And
a one wavelength horizontal loop is not a good omnidirectional antenna.
--
73, Cecil http://www.qsl.net/w5dxp



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Greg wrote:
"We would ideally like to put up an omnidirectional horizontally
polarized antenna like a loop."

FM and TV broadcasters do it and succeed amid adversity. In the US, TV
channel 2 is very near to 6 meters in wavelength. Now broadcasters may
opt for circular polarization, but in early times they used horizontal
polarization.

If crossed perpendicular dipoles are fed 90-degrees ouy-of-phase, the
combination is called a turnstile array.

The turnstile antenna produces a pattern that is nearly circular in the
plane of the turnstile. Due to the usual 1/2-wavelength of the turnstile
elements and coupling to their supports, there are often dimples in the
"circular" pattern which give an appearance of crossed figures of eight.
For practical purposes, the pattern circularity is usually good enough
for the turnstile to be accepted for VHF and UHF broadcasting.

Folded dipoles often make up the turnstile for the convenience of their
impedance when electrically connected in parallel and for the lightning
protection provided by closed-circuit antennas.

A single folded dipole is often wrapped into a halo shape with a small
gap between its ends for omnidirectional service and greater simplicity
than the turnstile. Capacitor plates are often added to the
short-circuited ends of the folded dipole to increase the capacitance
between its ends and thus improve current distribution which improves
pattern circularity. An array of such halos in a vertical stack can
provide gain by concentrating energy into a horizontal beam.

Phasing adjustments between elements stacked into the array of halos can
tilt the beam up or down from the horizontal.

High antennas often use a couple of degrees of downward beam tilt to
improve signals near the station and to reduce power loss in radiiation
toward the zenith.

Delaying the feed to each next higher element by an additional 4 or 5
degrees often depresses the elevation angle below the horizontal by a
degree or two.

Best regards, Richard Harrison, KB5WZI

Previously: "An array of such halos in a vertical stack can
provide gain by concentrating energy into a horizontal beam."
____________

N. B. A vertically stacked array of ANY kind of radiating element with ~ 1
lambda or less spacing can produce gain in the horizontal plane.

RF

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