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Author Topic: Un-conventional..or not?  (Read 1216 times)
K3JVB
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« on: June 04, 2006, 03:39:07 PM »

I have a pair of stacked Par loops for 6 and 2 meters.

I had them on a 30 foot height, just below my Hex beam. They are about ten feet below the beam. And pound for pound they work very well !

But...I do have a very tall (60 foot) tree, that would be usable for them. And would even be pretty stealth.

I would put them on a fiberglass mast, and secure it to one of the more vertical limbs. and the I think I could get them 65-70 feet up.

Any issues seen by anybody..I would think the extra 30 foot height could be a positive. Is it worth the effort?
Thanks
JohnB
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N9DG
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« Reply #1 on: June 04, 2006, 06:04:17 PM »

Depends. If it gets them above other nearby objects or thick foliage then it would be worth it. If the antennas @30 are largely in the clear already then benefits of the extra 30-ft of height will be minimal. Also consider the added loss of additional feed line, that alone may negate any advantage of another 30-ft. Another thing to consider is that in the tree they will likely sway much more. If the sway is large enough you will probably notice the effect on signals.
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WB2WIK
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« Reply #2 on: June 05, 2006, 08:30:06 AM »

A really tough call.

The tree is likely to sway a lot in the wind.  If you have a substantially long unsupported coaxial feedline between the tree and the shack, that will also bounce a lot in the wind and might require additional support, or at least a strong coax.  Squirrels in the tree might decide they like the taste of coax and chew through it.  Serviceability will likely be an issue.

However, gaining another 30-35' of antenna height on VHF is almost always worthwhile.

Rule of thumb regarding coax loss: On VHF, the height gain of an antenna system will always more than cancel the added coax loss provided the additional coax is vertical and not horizontal.  When I hear someone on VHF tell me their coax run is only fifty feet, my first response, without knowing anything about it, is, "That's too short."  It's too short because it means the antenna's too low.

There are exceptions, like mountaintop installations where another 30' often won't do anything because you're already 1000 feet or more above average terrain; but those are certainly exceptions.

WB2WIK/6
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K3JVB
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« Reply #3 on: June 05, 2006, 10:34:14 AM »

Thanks Steve..

I thought of almost everything. But I did forget the critters..LOL

And yes, I also did not consider the antenna movement, in the wind. I would think it will more pronounced on a VHF signal...tough call alright !
73
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KT4NR
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« Reply #4 on: June 05, 2006, 02:51:50 PM »

Let's back up a bit.

What kinda tree?

Pine trees hold a LOT of water and therefore absorb RF.

Dan S
KO1D
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K3JVB
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« Reply #5 on: June 05, 2006, 07:22:18 PM »

Good point..
It is a  Oak. And the plan is to get it up, and out of the tree top in the open, about 10 feet above it.
That would put it about 70-75 feet. And would require about 150 feet of coax.

I would be running about 20 watts on 2 ssb, and 100 or so on 6 ssb

JohnB
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WB6BYU
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« Reply #6 on: June 06, 2006, 10:48:05 AM »

A pine tree would be much easier to attach a mast to, due
to the straight trunk.  Oaks often don't have much in the
way of straight branches much above half way up or so.
Ideally you want to use as much of the tree as possible and
as short of a mast, because of how the tree sways in the
wind.  You may find that you have to attach the mast to
horizontal branches at two points rather than to a tall
vertical trunk, but the growth habits of oaks are far too
diverse for me to guess from this distance.
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