[amsat-bb] Re: Mode S Antenna question

Ronald Nutter rnutter at networkref.com
Sat May 10 14:43:33 PDT 2008

What got me thinking about the circular polarized type of antenna is to 
minimize the signal dropouts from the satellite as it spins.  My other 
thought was to put a second antenna up, orient it horizontally and put a 
remote antenna switch in place so that I can flip between vertical and 
horizontal.  Is my idea sound or am I barking up the wrong tree ?


Edward Cole wrote:
> 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
> 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.
> *****************************************************
> 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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