[amsat-bb] Re: ref my copy of ao-51

Douglas Quagliana dquagliana at aol.com
Sun Aug 10 16:31:51 PDT 2008

Hi Jeffrey,

you wrote:
 > hi folks, can anyone exlpain a little of this copy to us?

Since I haven't seen anyone else reply (yet) I'll
try to answer this. Remember: you asked. :-)

These are all packets sent from the onboard computer
aboard AO-51. The PECHO-11 callsign is AO-51's
broadcast callsign and the packets from this callsign
(and PECHO-12) will contain data in the Pacsat Protocol
format. This is the protocol that the onboard BBS
uses to send and receive data in a way that time shares
the satellite with all of the groundstations. Your
computer needs to be running a program like WiSP in
order for your computer to talk to the satellite using
the Pacsat protocol.  (I say "like WiSP" because there
are other program besides just WiSP that also speak
this protocol, but WiSP is probably the most popular.)

The TLMS and TLMI packets are telemetry packets that
contain information about the health and current status
of the spacecraft. The TLMI packet is sent as binary
data and you need a telemetry program like TlmEcho or
Sabins to decode the telemetry into meaningful values.
(Full disclosure: I wrote the Sabins telemetry program.
It's free if you want a copy and I don't make any money
from it.) If you received the 9600 baud signal with
a program like Willow, or if you saved the received
packets to a KISS file then Sabins can go back and show
you the decoded telemetry and what it means. Since the
data in the TLMI packets is binary you have to have saved
it as a KISS file, not as ASCII text, or you will lose
the binary data. If you use an Apple, then you need

 > PECHO-11*>PBLIST <UI>: PB: Empty.
The queue is empty. Probably nobody is using the
BBS right now.

 > PACBLS-8*>PACBLS-8 <UI>: PACBLS S Meter = 0
The S Meter reads zero right now (or at the moment
when the computer looked at the S meter).

 > PACB-1*>TLMI-1 <UI>: [and some binary data]
A telemetry packet. The binary data you put in your
email didn't make it through the mailing list, but
this packet will tell you all about the voltages,
currents, and temperatures on each part of the
spacecraft. Everything from the solar panels to the
battery control regulators to the radios to the
torque rod... and so on. It will also tell you
what is turned on and what is turned off. You need
tlmEcho or Sabins or MacEchoTelem to decode this
information so that you can see what this packet is
saying about the spacecraft. (Ok, you *could* do all
of the polynomial calculations by hand, but it would
be very tedious.)

 > PACB-1*>TLMS-1 <UI>: C0:0D C1:44 C2:76 C3:2F C4:04 C5:01
A simpler telemetry packet.  The "C" numbers are channel
numbers and the hexadecimal number after the colon is a
bitmask that tells you about things like the BCR DAC chip,
the transmitters, the torque rod commands, receiver
channels selected, CTCSS tones, some stuff about S band,
and so on. For example, C2:76 tells you that
- The RS-232 power monitor is OFF.
- CTCSS TXA and TXB do not have valid tone(s).
- Receivers 1 2 and 3 have their receive frequencies
  set to the main frequency.

 > PECHO-12*>BBSTAT <UI>: Open ABCD:
Again, more of "nobody is using the BBS right now."

 > PECHO-11*>STATUS <UI>: B: 120900539
This is a byte counter. Your software can save this number
and then when you get the next STATUS packet the software
can look at the new number and get a count of the bytes
(of certain types) that were sent by the spacecraft between
the two packets. You can compare that count to the number
(of those types) of bytes you received and see just how
much of the satellite's transmitted data you missed or
received in error. This gives you an idea of how good your
reception of the satellite's signal was between those two
packets. This number (apparently) does not increase for the
bytes in telemetry packets.

 >PACB-1*>LSTAT <UI>: I P:0x13A8 o:0 l:27208 f:27245, d:1 st:6 e:8b
Some lower level satellite status. For example, "d:1"
indicates that the AX.25 digipeater is enabled. If you
were to send a packet "VIA" AO-51, and if AO-51 heard it
without any errors, then AO-51 would retransmit your
packet on the downlink for everyone else to receive it.

For more information on the PASCAT protocols, see


(Note: there are some addendums to those documents.)

For more information specifically on AO-51, I recommend
"AO-51 Development, Operation and Specifications" by Gould
Smith. You should be able to get a copy if you call
Martha at AMSAT or via the AMSAT store at


And if you're really really interested in this sort of
stuff, you can get a copy of the "Digital Disk" which
includes WiSP. (Full disclosure again: I wrote a few
things on the Digital Disk, but again, I don't make
money from it.)

Good luck, and see you on the birds.

Douglas KA2UPW/5

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