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Author Topic: 2m Yagi and J-pole on same pole, need advice........  (Read 1383 times)
VE6FGN
Member

Posts: 18




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« on: April 02, 2011, 07:09:48 AM »

Just bought a 2m Yagi, and will mount it today. Plan is to have a J-pole immediately above it.

I'll run a separate line to each antenna, and will only use one at a time.

Can I stack the Yagi immediately (as in inches) below the J-pole, or do I need greater separation?

Many thanks- Garry
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KD8GKR
Member

Posts: 47




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« Reply #1 on: April 02, 2011, 08:08:18 AM »

will you be mounting the yagi vertical or horizontal?
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VE6FGN
Member

Posts: 18




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« Reply #2 on: April 02, 2011, 08:12:15 AM »

I'm trying to hit a repeater, so it would be vertical, correct?

Thanks- Garry
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KD8GKR
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Posts: 47




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« Reply #3 on: April 02, 2011, 08:30:18 AM »

Yep FM would typically be vertical. Depending on number or elements and boom length i would go for a 3-4 feet (1/2+ WL) separation.

What type of coax are you running on the J-pole and beam?
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WB6BYU
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Posts: 13239




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« Reply #4 on: April 02, 2011, 11:05:37 AM »

The problem is much more complicated than the interaction between the yagi and the
J-pole when the yagi is vertically polarized.  You have to keep the mast and the coax
from the J-pole out of the pattern of the yagi - this isn't an issue when the yagi
is horizontally polarized, but when the yagi is vertically polarized you have a few
options:

1)  Mount the back end of the yagi to the mast, so the mast and coax are behind
the reflector.  That usually means a shorter yagi, and the load is not balanced if
the mast is wobbly.

2) mount the beam on a side arm so it is spaced away from the mast.  Half a metre
of separate is probably adequate, a bit more probably is better.  This puts the mast
and coax to the side of the yagi, but again the load on the mast is unbalanced and
it makes it harder to rotate the yagi (unless the whole mast rotates.)

3) use a non-conductive mast (at least for the portion of it that passes though the
yagi) and route the coax from the J-pole out behind the reflector of the yagi.

Sometimes a good solution is to use two shorter yagis on a crossarm, one on either
side of the mast.  That gives a sharper azimuth pattern for the same overall gain,
but the mast has less influence on the yagi pattern.
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