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Re: antenna pattern



On Thu, 14 Mar 2002, el bachir zantou wrote:

> Could anyone help me find the radiation patterns of these two antennas: 5/8
> wave VHF whip antenna, and a turnstile. Where can I find drawings  to build
> a turnstile.

A plot of the 5/8 wave and a 1/4 wave monopole both theoretical and
measured are shown on my APRS Satellite web page below.   Look towards the
bottom of the page.

The live plots are easy to do by making 435/1575 MHz scale models of the
two antennas and then hooking them to a GPS receiver in the clear.  Than
just plot the signal strength, AZ/EL of all satellties coming out the
serial port for several hours and the result is a real world result.

The comparison plot (red and green) for the 1/4 and 3/4 wave antennas
actually used a 435MHz-to-1575MHz scale model of a car roof so that the
true effects of the roof gorundplane were seen.

Notice that the gain of a 3/4 wave vertical omni is almost 8 dBi which is
much better than a turnstyle from 25 to 70 degrees elevation.  The
turnstyle has a more even gain down to the horizon, but since satellties
on the horizon are 10 dB further away, there is not enough signal to
decode anyway...  So in my opinion, a trunstyle or eggbeater is just a
waste of 3 dB horizontal gain when you dont need it most of the time.

Of course, your mileage may vary..

de WB4APR@amsat.org, Bob

APRS SATELLITES     http://www.ew.usna.edu/~bruninga/astars.html

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