[amsat-bb] the SATgate donut effect

[Robert Bruninga]

The donut hole is a problem...  With two more APRS satellites to launch
this  year, we need -more- Omni Satgates with *lower* antennas.  The
vertical omni  1/4 or 3/4 wave satgate vertical antenna needs to be as low
as possible (to minimize the donut hole null and to reduce lightening
risk) while still seeing sky above 30 degrees.

See: http://aprs.org/aprs-satellite-igate-antennas.html

Once I deliver the last of these next two transponders, I hope to build
such a satgate with a D7 HT and document its performance.  I can place the
HT at the base of the antenna with near zero coax, and being low, it is
not vulnerable to lightening compared to surrounding structures.

Bob, WB4APR

-----Original Message-----
From: AMSAT-BB [mailto:amsat-bb-bounces at amsat.org] On Behalf Of
kb2m at arrl.net
Sent: Sunday, June 28, 2015 10:02 AM
To: amsat-bb at amsat.org
Subject: [amsat-bb] the donut effect

Is there anyway to get any APRS client to not Igate a packet with a path
of ARISS in it. I run a satgate here in NJ and the donut effect is causing
problems for several hams in the area that can't get a packet Igated after
it is digi'd by the ISS because it's a dup. My Igate hears the first
packet direct that then causes the ISS digi'd packet to be a dup.  It
would seem to be a simple thing to  set a filter to ignore a path of
ARISS, and accept everything else. I would think that this would fix the
problem of people who want to run Igates, but don't because of this. I
recently moved to Florida for the winter and had to shut my igate down in
NJ for this reason. Also,  I noticed when down there that there is a lack
of satgates along the eastcoast. ISS,PSAT, and PCSAT are hearing stations
fine but no satgate's available until the bird's footprint move well
inland.





73 Jeff kb2m



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