[amsat-bb] Re: Simple Newbie Q? SGATE?

Robert Bruninga bruninga at usna.edu
Mon Jan 14 11:28:33 PST 2008

> I am a newcomer to Sat Comm and began with 
> APRS activity through ISS.... On the APRS 
> through ARISS site it is suggested that success 
> will be improved by using "via ARISS,SGATE,WIDE" 

VIA ARISS gets it through the ARISS digipeater.

Normally, there is nothing else required since there are plenty
of satgates listening to the downlink that will feed it into the
global APRS system and the various web pages. 

However, I was told that some remote satellite downlink stations
in Australia do monitor ISS all the time, but they have no
internet access.  SO they set their base stations up as a
cross-frequency digipeater with the ALIAS of SGATE so that when
their station hears a packet via ARISS, they can digipeat it
over onto the local APRS frequency which will then digipeat it
VIA WIDE where hopefully a terrestrial APRS gateway will hear

This is very convoluted and confusing.  I do not think it is
worth it.
Because then also the packet arrives shwoing the last digi was a
terrestrial digi and so the packet will not be captured as
"being heard via ISS"...

> other info says: NEVER use GATE in a VHF path---

That refers to VHF and HF gateways using the specific gateway
call of "GATE".  We do not want to see 1200 baud VHF traffic
forced blindly onto a nationwide 300 baud HF system.

> then what exactly is SGATE? 

It is just a next option in the path.  Sometimes when we want to
hear PCSAT-1 via PCSAT2, we could set the PCSAT-1 telemetry to
go via SGATE.  Then we could add SGATE as a digipeating alias on
PCSAT2 and it would digipeat those packets for a dual hop
satellite link.  Its just a generic
Digipeater name.  Sometimes used, sometimes not.

> I see that ISS uses SGATE on its own 
> announcement messages but I see very few 
> uplink messages using it.

That was for the Austrailains as noted above.

But generally, do not add extra hops in your path if not needed,
since they add 7 bytes per field as overhead.  Longer packets
always have worse reliability than shorter ones.

> Also, if I am only wanting to utilize messages 
> into my current sat footprint, is RFONLY a 
> good path statement?

If you really do not want to make it to the internet, then you
could use the path VIA ARISS,RFONLY.  But again, that's 7 bytes
that are not needed.

> I was successful on several occasions using via 
> RS0ISS-4,SGATE,WIDE  so it works but I don't 
> want to be hogging up resources.

Not unless you are in Australia.  Otherwise, it just makes your
packets longer.  And by now. Maybe that one satgate in Australia
has gotten his own internet and we don't have to do this kludge.

Bob, WB4aPR

> Thanks for your patience,
> KU8L 
> EN82hi
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