I have the Alpha-Delta 80 meter dipole as inverted V on my 150 foot Rohn 45
tower. It is suspended from 90 feet, and hangs off a short piece (about 4
or five feet) of 1 inch PVC tie wrapped/taped through the tower (sticking
out about 2 feet). The legs are tied off at about 200 feet from base of
tower. It is direct fed with LMR400 coax. VSWR is close to 1:1. This
antenna was installed several years back when guys were 1/4 EHS. All have
been replaced with Phillystran, but this change did not affect VSWR to any
extent. VSWR measurements were made with MFJ259, and later with MFJ269 that
replaced it when it went south.
I am wondering if your aluminum stand off is causing the problem.
Keith NM5G
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of Robin Midgett
Sent: Wednesday, September 29, 2004 3:14 PM
To: towertalk@contesting.com
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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_______________________________________________
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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