[amsat-bb] Re: GO32 APRS ?

Robert Bruninga bruninga at usna.edu
Thu Sep 18 12:01:54 PDT 2008

> I seem to fail to understand the APRS mode of GO32:
> This is the only source of documentation I have:
> http://web.usna.navy.mil/~bruninga/GO32-ops.html
> Which states:
> 145.85 MHz All APRS messaging (or fixed station non-Mic-E 
> positions). . Only TOCALLs that begin with "APxxxx".

This is because APRS messaging uses an AX.25 Destination Address
of APxxxx where xxxx is a version number.  I call that AX.25
Destination address the "TOCALL" for brevity...

And on 145.85 uplink, the GO-32 satellite IGNORES any packet
that does not begin with the AX.25 DESTINATION address that
begins with "A".

> 145.93 MHz All APRS Mic-E positions and 
> status(D7, D700 and  D710s with comment set 
> to "Committed, Special or PRIORITY"...

On the 145.93 UPLINK, the GO-32 folks opened up additional
INITIAL bytes of "2,3,4, or 5" as possible AX.25 DESTINATION
addresses.  In this case, a Mic-E packet at any LATITUDE between
20 to 59 degrees latitude will begin with one of those digits.
... But only if the "comment" set to the above selections.
Because if they are not set to that selection, then the
additional bit is used and the leading byte of the AX.25
DEESTINATION field is no longer a digit from 2 to 5.

The reason the GO-32 (and ECHO, AO-51) and other PACSAT-BBS
Protocol birds have to have this first-byte filtering, is so
that the constant NOISE in the receiver does not forever trigger
the 9600 baud interrupt and consume inordinate amounts of
processing power on noise.  By ignoring all false detections
except those that begin with the very first matching byte, then
the CPU can ignore 255 out of all 256 possibilities of noise.

> The reason for these uplink distinctions is due to GO-32 
> hardware that will only digipeat a packet on 145.85 that has
> a TOCALL beginning with "A". (All APRS fixed station packets 
> and all APRS messages including D7 and D700's) . The
> 145.93 channel will only accept packets that begin with a 
> digit between 1,2,3,4,5,6,7. . But fortunately the D7 and
> D700's do this naturally as long as the position comment is 
> set to "committed, SPecial or PRIORITY"...
> Q1: do the TOCALLs need APxxx or Axxx on 850 ? 
> (in CONV mode type :APxxx ?)

The TOCALLS really refers to the AX.25 DESTINATION address.

> Q2: should here ":2xxx" work ?

Neither of these will do anything.  I think you are thinking of
the APRS MESSAGE TOCALL, and that can be anything.  But it has
to be the complete format.  As in  :APRSTOCAL:message text.  It
must be 9 bytes long ad begin and end with colons followed by
text.  The BEST APRS messages to send via any satelite should be
addressed to :ALL......:hello world..., beause ALL APRS radios
will capture a message to ALL.  Otherwise it will ignore it.
Notice that the ... Dots have to actually be SPACES to work.

> Thanks !
> Henk, PA3GUO
> .... so lost :-)
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