Cecil Moore wrote:
On Jun 3, 11:03 pm, wrote:
But feeding a whip with a tuner usually does not
make for an efficient mobile antenna.

A 11.5 foot (~3.5m) whip driven by an SG-230 autotuner was measured to
be 12 dB down from the top-rated bugcatchers and screwdrivers at one
of the CA 75m mobile shootouts back in the 1980's.


that's a pretty big difference.. (12 dB implies a factor of 16.. that's
like most of the Tx power being dissipated somewhere, and that sounds
like "component melting" levels)

Have you a link to the data and test methodology?

On Jun 7, 11:36*am, Jim Lux wrote:
* Have you a link to the data and test methodology?

I summarized the data from three CA 75m mobile shootouts at:

http://www.w5dxp.com/shootout.htm

I don't recall a test methodology being published. The test receiver
consisted of a ferrite loop antenna in the far field feeding a lab-
grade RF voltmeter. The power incident upon the 75m mobile antenna
system was assumed to be forward power minus reflected power on the
coax to the antenna system, measured using two Birds. The receive
results were normalized accordingly. I may have left out a detail or
two.

The SG-230 plus 11.5 whip at -12 dB was equal to a 75m hamstick. I
entered both the top-rated (0 dB reference) antenna and the (-12 dB)
autotuner+whip on the same vehicle. When I "superposed" all of the
three results, I assumed 0 dB for each top-rated antenna and let the
rest fall where they might. That may or may not have been a reasonable
assumption.

I suspect the SG-230 is designed to dissipate 100 watts (using large
#2 material powdered-iron toroids). During one shootout episode, I
forgot to attach the antenna to the mobile mount. The SG-230
faithfully tuned to close to a 1:1 match on the input - with a near-
infinite SWR on the output. It was a damp foggy day and the mobile
mount arced. That taught me not to mount the SG-230 unobserved in the
attic. :-)
--
73, Cecil, w5dxp.com

Cecil Moore wrote:
On Jun 7, 11:36 am, Jim Lux wrote:
Have you a link to the data and test methodology?

I summarized the data from three CA 75m mobile shootouts at:

http://www.w5dxp.com/shootout.htm

I don't recall a test methodology being published. The test receiver
consisted of a ferrite loop antenna in the far field feeding a lab-
grade RF voltmeter. The power incident upon the 75m mobile antenna
system was assumed to be forward power minus reflected power on the
coax to the antenna system, measured using two Birds. The receive
results were normalized accordingly. I may have left out a detail or
two.

Were those all mounted in the same place on the same vehicle, e.g. the
license plate bracket?