[amsat-bb] Re: Mode S Antenna question

[Edward Cole]

At 05:26 AM 5/10/2008, Ronald Nutter wrote:
>I have been using a 2.4 ghz Vagi antenna for my Mode S antenna the past
>few days.  I am seeing quite a bit of signal droppout as AO-51 does a
>little rotating.  With a circular polarized antenna do any better ?  I
>have found a source for a 2.4ghz 10 db RHCP antenna and thought about
>trying that.  I know I cant get it before AO-51 goes back to V/U mode
>but thought I could try that next time.  The antenna I found has about a
>50 degree pattern so I should get decent coverage since I have it
>pointed at a fixed elevation because I dont have an az/el rotor.
>
>Ron
>KA4KYI

Ron,

 From what I have read on what others are using for 2.4 GHz (mode-S) 
on AO-51 (or other Leo sats) a 10-dB circular pol. antenna should 
work fine.  As far as using it without elevation control I cannot 
tell you how that will work.  Ten dB may be a bit too narrow for best 
operation at all elevations.  But the gain would be good to have 
for  the period of time the satellite is within your beam.  I believe 
Bob Bruninga has found that a fixed elevation of 20-degrees makes a 
good solution when not moving elevation.

If the antenna is accessible you can experiment on what angle works 
best by trying it at several angles.

I plan to build my self a simple corner reflector fed with a dipole 
which should result in about 10-dB gain.  I also have an 85cm dish 
with helix feed that was used for AO-40.  I have two 2.4 -GHz LNA's 
and two Drake converters (123-MHz; 435-MHz output) so that any 
combination will be possible when all is re-installed.  I have full 
az-el tracking.




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73, Ed - KL7UW              BP40iq, 6m - 3cm
144-EME: FT-847, mgf-1801, 4x-xp20, 185w
http://www.kl7uw.com     AK VHF-Up Group
NA Rep. for DUBUS: dubususa at hotmail.com
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