If you are feeding directly with no hairpin the feed point impedance will
cause high VSWR. You can make a hairpin equivalent from three turns of 12
gauge solid copper wire wound on a 3 inch form. Leave about 1.5 inch at
each end for spade terminals to connect to the antenna feed point. After
installation, tune shorting bar for resonance, then spread coil slightly to
minimize VSWR at resonance.
To prevent RF current from conducting to the feed line (coax shield), use a
current balun or RF choke at the feed point.
73, Keith NM5G
[mailto:email@example.com] On Behalf Of Martin Sole
Sent: Saturday, August 06, 2005 5:03 AM
Subject: [TowerTalk] EF140 antenna problem
Just put together an EF140 that was removed woking from a friends QTH. Put
it on the tower about 30 feet up so I could easily get to it for adjustments
and measurements. My MFJ259B says SWR is 1:1 at 8MHz and about 14:1 at 7MHz.
I have moved the linear loading wire jumpers to the most LF setting. Can't
think of anything else. Is there supposed to be anything across the
feedpoint some L etc? Original owner cannot remember and we couldn't find
anything. Any ideas.
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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.
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