Peter,
?
3 dB is what we've measured using S-meters from an
Icom 756ProIII, so for what it's worth. Coupling from the vertical also occurs
with the 5 inch loading coil, I can see if cars are passing on the other lane by
looking at the VSWR. Even lightpoles, traffic signs etc result in detuning. This
sometimes results in a fast flutter, as reported by fixed stations during mobile
QSO's on 80 meter.
?
On next occasion I will do a temperature
measurement on?a centerloaded vertical with a 3" and 5" loading coil, in
order to get a better?impression of the dissipated RF in the coil. But,
without doubt there is a significant difference in antenna performance when
the?loading coil goes from 1.7 inch to 5". The difference between a High
Sierra HS1500, featuring a 1.7 inch diameter loading coil and a HiQ 5-80 with a
5 inch loading coil was 10 dB on 3600 kHz.?I rember?the loading coil
on the 1.7 inch antenna ran hot to the touch and the contactor almost burned
out.
?
Cheers, Dick
PA3DUV
?
?
?
?
?
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----- Original Message -----
Sent: Thursday, January 11, 2007 3:01
PM
Subject: RE: [ham_amplifiers] Re: hi
power mobile
Hi Dick,
That is very unlikely at same wire size.
3db difference
would mean half of the transmitting power being lost across
the
coil.
The ARRL program "mobile" calculates 1,3db difference.
But you are
right, the larger coils give no remarkable improvement, but make
it much
easier with tabs for band change.
The disadvantage is the detuning while
passing trucks.
73
Peter
________________________________
From: ham_amplifiers@yahoogroups.com
[mailto:ham_amplifiers@yahoogroups.com]
On
Behalf Of PA3DUV
I found approx. 3 dB difference between a 3 and 5 inch
loading coil in on
air test on 80 meter. Anything larger than 5 inch the
difference was
neglectible.
