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Re: Mobile 9600 Baud Station



At 08:58 AM 11/2/98 -0800, you wrote:
>Now, the one thing that has eluded me is what to do about mobile antennas.
>A steerable array on my roof at home is great, but not too practical on the
>roof of the motorhome. I have tried  every kind  of verticle antenna I
>could think of. The 70 cm 1/2 waves have done the best job, but even they
>are marginal. I am using a GasFet preamp in the shack with 15 feet of 9913
>going to the antenna. As for transmitting, not one single 2 meter mobile
>antenna I have tried has even given marginal success with 45 watts out.

Hi Bob,
At the last AMSAT Space Symposium, I presented an quantitative analysis
of receiving on 436 MHz with an "eggbeater" style antenna. This
antenna is better than any vertical. However, on the 9600 bps satellites,
even this antenna will not give you a sufficient signal-to-noise ratio
to copy very much. A Lindenblad would work a little bit better. However, based
on my numbers, I do not think that ANY omni-directional antenna would 
provide GOOD performance. Your best bet might be to "hand-point" a 
small circularly-polarized beam (Yuk!) You need something around 10 dBic gain.

A vertical is also not very good for transmitting. (See my article in the
April/May AMSAT Journal 1996.) Even cranking the power up will not do it!
For transmitting, a Lindenblad will provide significantly better performance 
but you still might have to crank the power up depending on the "competition"
in your area (on the east coast this is pretty steep!)
Good Luck and 73,
Tony





Tony AA2TX@amsat.org
Tinton Falls, NJ

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