[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: Re Satellite Mobile Antennas



Here is an elevation plot of a 19" whip antenna
over a ground plane acting as a 3/4 wave on 435 MHz.
See the plot about 80% down my ASTARS page:
http://www.ew.usna.edu/~bruninga/astars.html

It is easy to make a LIVE elevation plot of ANY
vertical antenna by simply making a SCALE model
of it scaled to 1575 MHz.  Then set it outside in
the clear hooked to a GPS.   Then just capture
the GPS data over several hours, and then
parse the strings to pull out the reported AZ and
EL and SIGNAL strength from thousands of points
all over the sky.  Plot it, and the result is the real
live signal plot of that antenna.

I even put my model on a bent piece of metal the
SCALE size of the roof or my car.  So the plot was
as real as I could get.

The plot is not really calibrated in dB, but just the
relative signal strength reported by the GPS, but
it is reproducible.  Also, you can run it again with
a real 1/4 vertical (scale) and that gives you a
real comparison.  You can see that the 3/4 is
significanly better above 30 deg and significantly
worse below 15 deg.

WIth two GPS's on both serial ports at the same time
you can do two different antnenas at the same time.
Usually one being the 1/4 vertical for the reference
or you can do them at different times.


Bob, WB4aPR

>>> "Mike Hooles" <Mikehooles@btinternet.com> 09/15/05 9:01 AM >>>
Hi Guys and Girls,
Many thanks to those who suggested that I use a standard 2 metre quarter 
wave for LEO satellite mobile on my vehicle, poinimg out that it would 
automatically be 3/4 wavelength on 70cm.. As an HF man I should have 
remembered that.
I had been using several makes of combined 1/4 wave 2metre up and 5/8 70cm 
down antennas with moderate success, but after a couple of months they 
degraded, probably due to the vibration of my diesel vehicle and being 
thrown into the boot when not used.
I built up the quarter wave whip last weekend using a standard magnetic 
mount, 3/8" screw,   tuned it and achieved an swr of better than 1.5 across 
the band on both 2 metres and 70cm.
Operationally it is performing better than my previous antennas and is much 
more robust.
Has anybody got a polar plot for a 3/4 wavelength ground plane , or full 
antenna as I cannot find one in any of my literature and have not located 
one on the web,

Best regards
Mike G3LGR
33643 
----
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
Not an AMSAT member? Join now to support the amateur satellite program!
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
----
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
Not an AMSAT member? Join now to support the amateur satellite program!
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org



AMSAT Top AMSAT Home