[amsat-bb] A suggestion for ... Emergency Comms - 1200 bd 10m uplink.

Robert Bruninga bruninga at usna.edu
Fri Dec 15 18:04:41 UTC 2017

Actually, why wait till Experimental Wednesdays.

1200 baud AX.25 packet is legal uplink for PSAT's 28.120 USB uplink and
435.350 downlink (unless I misread the rules).  SO I will say that such
experiments are welcome on PSAT as long as there is little to no other PSK31
activity in the 1000 to 2400 Hz tones on the air at the time of the
experiment.  Doppler during a 1 second packet burst will be

OOPS, insignificant, but critical.  One has to pre-shift your uplink so that
your downlink does come down at the standard 1200 baud AFSK tones of
1200,2200 Hz.  I guess the key there is to transmit your PSK31 "pilot"
signal for a few seconds at say 500 Hz on the uplink, adjust your uplink
Transmitter RF to verify you see it at 500 Hz in the downlink and then
transmit the packet.

I'd love to see this transponder used more.  But again, the uplink is shared
with terrestrial PSK31, so share the band.   You can verify a clear band by
looking (or listening) in the downlink if there are ANY PSK31 users in the
1000 to 2400 Hz bandwidth prior to transmitting.


-----Original Message-----
From: Robert Bruninga [mailto:bruninga at usna.edu]
Sent: Friday, December 15, 2017 10:03 AM
To: amsat-bb at amsat.org
Cc: Robert Bruninga
Subject: A suggestion for ... Emergency Comms - APRS...

Such a highly compressed method of satellite encoding exists called APRS.

>> ... the limiting factor for using LEO satellites as an Emergency
>> Response of any scale, would the short amount of time of a given pass
>> and the limited number of usable passes a day...

> But, us ingenious ham radio operator types perhaps have the basis of
> sending compressed data which conveys a lot of information.
> Packed into the bytes of telemetry messages ...
> How about a predefined disaster status data stream that all shelters...

Use the APRS Object for a SHELTER.  Just one packet can contain the
position, time and date of the report, and up to 47 bytes of useful info
such as 1) head count of staff 2) head count of victims 3) electrical power
4)drinking water 5) more supplies needed 6) need critical assistance.

> Conversely, if multiple LEO satellites support a disaster-status

They do.  APRS is currently on 3 sateliltes... PSAT, ISS and PCSAT and soon
to be QIKCOM2 and PSAT2 and BRICSAT2... And TJHS hicghschool cubesat, etc

> We'd need future cubesat missions capable of supporting a disaster
telemetry stream.

We have it.  See the SATT4 single card APRS transponder.  We invite every
school or university that is contemplating a CUBESAT to consider using this
transponder for their command and control which also provides the APRS
transponder as well.  Cost is under $300 or so.
See http://aprs.org/satt4.html

Bob, WB4aPR

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