Here is a little data in a sea of complexity:
My 160m T is 10' up at the base with 6 x 125' radials elevated ten feet
(4 more planned), in a mixed hemlock/red cedar/alder forest/clear area.
The top is at 87' and the T arms are 42' each side at the same height.
The vertical wire (13ga insulated CCS) is about 18" from the trunk.
When I put it up, one T arm snagged on branch stubs on the supporting
healthy hemlock and only extended out about 17'. The other 25' was
tight (3-4") to the trunk. Fed thru a 50::25 ohm balun and 4000k ohm
choke the resonance was 1835KHz and swr 1.1:1 - victory!
Then I had a tree climber remove the branch stubs, and clear a few
interfering branches at 90'. The problem arm was extended to its full
length. Now both arms are 42' each side pretty much in the clear.
Resonance dropped to 1785KHz. So, now I need to lower everything and
cut off some wire. All the original dimensions were chosen by EZNEC for
1835, so the tree loading had/has a significant effect, as luck would
have it, to right on the design numbers with the snagged arm.
This thread has been helpful and now my plan is to have the high voltage
parts of an antenna away from living wood. If I ever redo the
installation, I would also opt to move the top of the vertical section
as far as mechanically feasible from the tree, probably 3 or 4'. An
even better solution would be to support the whole T between two trees,
but that won't work for my radial field. Keeping T arms away from wood
by 5 to 10' seems like a good idea IMO.
As far as performance, I have no way to verify it. This is my first
"serious" 160m antenna and I felt in last winters SSB contest (my first
160 contest also) it wasn't a great performer. But from 48N (Redmond,
WA) we "suffering sevens" are frequently wondering who the folks in
1,2,3,4, and 5 land are talking to. 64N sounds like a heck of a challenge!
However, it "looks good" so should "work well," particularly since it
will be "improved" for the next contest.
Grant KZ1W
On 8/9/2013 9:31 PM, Gary and Kathleen Pearse wrote:
Where are the high voltage points in a "T" antenna?
I have the choice of putting up either a new T between two trees, or an L again
on 160M. The ends of the T would by necessity be strung over and go down 20-30'
alongside the two supporting trees.
The L would parallel a tree and bend over at around 75-80'. The horizontal end
of the L would end up 20-30' from its tree support. I'd reuse my 8 tuned
elevated radials, plus maybe a couple more.
Suggestions? Sometimes high angle works better in our tilted ionosphere at 64N.
73, Gary NL7Y
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Topband Reflector
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Topband Reflector
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