Mike--
Often, quoting eHam is repeating nonsense. Sorry, but it is so, and this is
a good example. Any Ham that relies on published Velocity factor data,
without verification, gets errors, and (frequently) blames it on something
else.
Start over; read some texts or handbooks; Think; read stuff from people like
W8JI (and people he disagrees with).
Reading eHam is like reading Antennex; There may be something good there,
but how can you tell? It's not checked by anyone qualified.
Bill--W4BSG
-----Original Message-----
From: mike l dormann
Sent: Monday, December 10, 2012 2:46 PM
To: topband@contesting.com
Subject: Topband: Fw: Re: : antenna question ...this is not going to
dieqiuite yet....................
if I may quote eHam.....
Dale Hunt:
The velocity of typical cheap TV twinlead is usually in the range of
0.8 to 0.85 (and can vary along a single role.) This is important if
you are creating a quarter wave matching stub, but not for the
overall length of a folded dipole antenna. Use the standard single-
wire dipole formulas and it should work fine.
One variation I have seen is to connect a short jumper wire across
the twinlead a short distance in from each end of the folded dipole.
The idea is that, while the overall antenna length is not corrected
for the velocity factor, each half of the antenna is effectively a
quarter-wave stub which does need the correction. The shorting
bar is put on each side about 85% of the way out from the center.
This may improve the SWR somewhat in a 300 ohm system, but
if you are using a tuner to match 50 ohms to 300 ohms, then you
won't seem any noticable improvement. (The tuner setting will
compensate for any slight mismatch due to the velocity factor.)
I guess if one was to use a balan of some sort to have the end to the
transmitter be 50 ohms, this could of of some importance
mike w7dra
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