[aprssig] APRS Satgate Antenna page

Stephen Black kb1chu at aol.com
Tue Jun 23 19:48:58 CDT 2015


One question,what constitutes a large ground plane? Is it 12"or 12'? Is 
it a multiple of the vertical whip?  Inquiring minds want to know. 
Thanks Steve KB1CHU



On 6/19/2015 3:57 PM, Robert Bruninga via aprssig wrote:
> Subject: APRS Satgate Antenna page
>
> Since the ideal APRS Satellite IGate OMNI antenna is exactly the opposite of
> the typical terrestrial IGaate antenna, I prepared the following WEB page:
>
> http://aprs.org/aprs-satellite-igate-antennas.html
>
> It shows how a vertical ¼ or ¾ wave VHF omni equals the performance of a
> full OSCAR class array (over half the sky) but does it with no moving parts.
> It makes up for the weak-signal horizon part of the sky by there simply
> being more omni-IGates.  The APRS-IS cloud with all of its IGates is
> probably one of the largest spatially distributed satellite receiver system
> in the world (?).
>
> But with people used to the 10W transmitter on the ISS, just a few IGates
> can capture just about every packet from the ISS horizon to horizon on a
> whip.  But with the 14 dB weaker signal from PSAT, we need more SatGates to
> make up for their smaller skyprint.  For the USA we need more than a dozen
> such Omni-SATgates.
>
> To see the significance of the weaker downlink from PSAT, look at the
> successful IGates on the http://pcsat.aprs.org page compared to the IGates
> that hear the ISS packets on http://ariss.net   Both are listening on
> 145.825 and passing along every packet they hear.  But only TRACKING IGates
> or good vertical gain satgates hear PSAT. And since we want these running
> 24/7/365, we do NOT expect people wearing out motors when an omni will do
> fine (if we have enough).
>
> The page also shows how every SATgate with a HIGH and terrestrial type
> antenna actually creates a DEADZONE around it, effectively blocking any
> nearby user heaerd direct from appearing on any of the APRS-IS cloud
> satellite web pages.  Hence, Omni-satgate antennas should be low to
> everything surrounding it w hile still seeing the sky above 30 degrees.
>
> If your TH-D7 HT is just sitting there, not in use 99% of the time, then
> just hook it to a vertical whip and let it be an IGate.  With the low
> antenna it will also probably be safe from all weather lightening too.  Put
> the UHF side on 435.350 and turn up the speaker.  When PSAT PSK31 comes into
> view, you can watch the PSK31 activity as a bonus!
>
> Bob, WB4APR
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