[amsat-bb] Re: GO-32 APRS experiments Tuesday

[Robert Bruninga]

> ... Tuesday on the 9 and 10 AM EDT passes over 
> the East Coast, we hope to do a student
> demonstration of APRS packets via GO-32.
> 
> We will be looking for other APRS stations and 
> trying to message anyone we see.  If anyone can 
> run their sat station as an IGate, that too 
> would help us capture all packets.

GO32 and AO-27 share the same APRS home-station 145.85 uplink,
but now they are almost exactly out of phase, so there is no
uplink conflict.  GO-32 comes over between 8 AM and Noon or so
local sun daylight savings time in the USA latitudes.  AO-27
comes over in the afternoon. 

Any UI packets are welcome from any station using any 9600 baud
hardware.

If you have a D700 with built-in 9600 baud TNC, then set your
mobile for these parameters while your car sits in the parking
lot tomorrow morning.  The mobiles use a different uplink
without conflict to AO-27.

Set APRS Baudrate to 9600 baud.  
Set A band to uplink on 145.93
Set B band to receive 435.225
Set Path to be via 4XTECH
Set MYCALL to a unique SSID
Set TX method to AUTO
Set TX RATE 1 min for HT. 2 min for D700
Put something useful in your STATUS text maybe describing your
setup: "50W mobile, 1/4 wave, 2m rate" or "5W HT, long whip, 1m
rate"

Save in a PM for use anytime you are outside of the terrestrial
APRS network.

SATELLITE OPERATING NOTES:

The uplink is on the order of 20 dB more effective than the
downlink.  Menaning it is easy to get in, but difficult without
a beam to hear it.

See my GO-32 APRS operations web page:
http://www.ew.usna.edu/~bruninga/GO32-ops.html

ACCESS TIMES:  GO-32 is sun synchronous and so it comes over
everywhere at USA latitudes three times between about 8 AM to
Noon and again between 8 PM to midnight local sun time.  During
these two windows at least one pass each will be an overhead
pass which might also work for an HT.  The other passes will be
lower to the East or West and will work fine for a 50W mobile.

WHAT YOU HEAR:  9600 baud sounds almost exactly like open
squelch, though the tuned ear can soon distinguish the
difference.  Before the pass, set your squelch normally to quiet
the speaker.  When you hear the satellite, the squelch will open
and you may see up to 3 bars on your S meter.  Tune to the "best
sounding" noise.

DOPPLER:  Depending on how low to the horizon you can see, the
satelite approaches 10 KHz high at 435.235 MHz... But it is
maybe 3000 km away.  As it gets higher, and 6 dB closer, it will
be on 435.230 MHz, passing through 435.225 published center
frequency at the middle point, and then drop down through
435.220 and ending at 435.215.

But since it is 6 to 10 dB closer (and stronger) towards the
center of the pass (800 km overhead), the mobile antenna is
probably only going to hear the middle 435.230, .225, .220
portion easily.  So I would start my receiption at 435.230...

UPLINK CHANNELS:  GO-32 allows two APRS uplinks.  One is
exclusive to Mic-E formatted (Think D7/D700) tactical position
reporting and the other exclusive to messaging.  This is in
hardware, not policy...

1) All APRS messaging (or fixed station non-Mic-E positions)
must use the 145.85 uplink where GO32 only digipeats APRS
packets with TOCALLs that begin with the usual "APxxxx".  (Even
the D7 and D700 use "APKxxx" for messages.)
 
2) All APRS Mic-E position uplinks (D7, D700 and D710s) must be
on 145.93 MHz and they must have the position comment set to
"Committed, Special or PRIORITY"...  With those comment settings
then the TOCALL first LATITUDE digit will be 1,2,3,4,5,6,7 and
only these will be accepted by GO32 for 
digipeating from 145.93.

DATA CARRIER DETECT: The D700 and non(g) model D7's will NOT TX
if they are hearing the downlink at the same time due to CARRIER
DETECT.  The D7(g) model has DCD IGNORE that *will* let it TX
anyway.  So use separate rigs for TX and for RX if you want to
see yourself.

Otherwise stick to the receommended TX rates and know that you
are getting in if you stick to the protocol.  Sticking to the
recommended rates also keeps channel loading low, so that
everyone gets in with less congestion.

The D7 can get in with a 19.5" whip during the center of the
pass.

Here is a link to AMSAT's description of GO-32:

http://www.amsat.org/amsat-new/satellites/satInfo.php?satID=14&r
etURL=/satellites/status.php

Good luck!

Bob, Wb4APR