Owen Duffy wrote:
Ed wrote in
. 192.196:



I just started using the ARRL provided program, mobile.exe , for
some
mobile antenna design work. I see that one of the figures required
to be input is ground loss.

Which raises the issue for me, how does one measure, ( or
calculate),
the ground loss in a mobile antenna.


Ed, I assume you mean ground loss stated as an equivalent series
resistance.

If you measure the feedpoint impedance or the VSWR of a short loaded whip
at resonance, you have a figure total resistance either directly reading
or from VSWR, R=50/VSWR. (Of course, those measurements need to be made
without any impedance transformation even if you might use such in
service.) That feedpoint resistance comprises equivalent ground
resistance and the equivalent of the antenna losses and radiation
resistance. If you can estimate the second component from models, the
equivalent ground resistance can be estimated by deduction of the
equivalent radiator R from the measured feedpoint R.

I would suggest that for the purposes of rough and ready estimation, and
considering the measurement uncertainty from most ham measuring gear,
you could estimate the radiation resistance of an 8ft long mobile
antenna without a tophat at being about 25-30 ohms for 10m, 5.5 ohms for
20, 1.5 ohms for 40, and 0.4 ohms for 75/80. Probably close enough with
about 1.5 significant digits accuracy.

Jefferies has similar numbers at:
http://www.ee.surrey.ac.uk/Personal/...es/radimp.html


Jim, W6RMK