Sometimes simple antennas can drive you crazy when they don't work. I see
no reason to move the center further from the tower. It's very likely that
the guy wires are causing the problem, however I have occasionally seen
strange things with my MFJ antenna analyzer, especially on low band dipoles.
Can you hook it up to a rig and confirm the analyzer results?
GL,
John KK9A
----- Original Message -----
From: "Robin Midgett" <robin.midgett@vanderbilt.edu>
To: <towertalk@contesting.com>
Sent: Wednesday, September 29, 2004 20:13
Subject: [TowerTalk] 80m Newbie...Help w/ Inverted V Please
Hi,
My attempts to make an inverted V resonate on 80m are not meeting with
great success. I've put up inverted V antennas before (10m & 40m) and they
worked very well...not so in this case; 2.8:1 (feed point fully up) is the
best match I've seen yet. I'm hoping some of you more experienced will have
some constructive input.
Here's the configuration:
130' of Rohn 45G, on fairly flat, level ground with a 24" (out from the
tower) aluminum stand off bracket at the 60' level. A rope and pulley rig
is used at the end of the stand off to haul the feed point of the V up to
the 60' level. Each leg of the V is ~62' long, and there is ~ 80-90
degrees between them. The ends of the wire (14 ga. stranded) are formed
into a loop, which is where a small piece of rope attaches and anchors to a
stake in the ground. Pretty typical stuff, from all I've seen before.
The tower is guyed at 30' intervals to posts 85' from the tower base, so
guy wire lengths (all 1/4" EHS) are 90', 104', 124' & 127', no insulators
on any of them.
With the feed point pulled up all the way, ~3:1 is the best match I get. If
I lower the feed point to ~50', and the ends of the wires are drooped onto
the lawn, the match improves to ~1.8-2:1.
I'm using a MFJ-269 to make the measurements. I find really good matches
(~1.5:1 or better) at 12 MHz, and odd multiples up the bands.
I've changed the coax, no help. Removed the coiled coax choke; no help.
Checked continuity from shield to end of one wire, OK; from center pin to
end of the other wire, OK; no shorts, either.
Is this possibly a case of guy wire coupling/interaction? Might raising the
feed point to a higher level help the match? Should I extend the distance
from the side of the tower to the feed point?
Thanks,
Lost in H.F....going back to VHF+....Robin KB4IDC
"Success is the ability to go from failure to failure with no loss of
enthusiasm." -Winston Churchill
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
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TowerTalk mailing list
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http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
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