[amsat-bb] Re: Data signal in FO-29 passband

Douglas Quagliana dquagliana at aol.com
Tue Jan 21 22:50:45 PST 2014

Hi Ken,

Hope this helps:

The output below certainly appears to be AX.25 in KISS format with the 
ASCII characters translated to perhaps something like Windows Arial font.

The a-grave (the "A" with the backwards accent) is hex C0, which is the 
KISS frame delimiter
that appears at the start and end of each KISS packet. There are two of 
them after "UTC"
indicating that the first frame is the date/time in UTC. There is 
another one at the end
after "test".

The second frame contains extended ASCII characters similar to the way 
callsigns appear
in AX.25. The hex values for these (from the second a-grave after UTC 
through to just
before "This") appears to be

9E A6 86 6A 68 6C DB DC 8E A6 B0 6E 68 72 20 03 F0

[footnote 1] (assuming that all of the characters made it through the 
mailing list
intact and correct, which I'm not sure they did)

 From this byte sequence, "DB DC" is a KISS byte sequence for Frame 
Escape (DB),
Transposed Frame End (DC) which means that the over-the-air byte was
actually a hex C0. [ footnote 2]

Substituting "C0" for "DB DC" This gives us the hex sequence

9E A6 86 6A 68 6C C0 8E A6 B0 6E 68 72 20 03 F0

If we assumed these bytes represented callsigns and right shift each 
byte in the same way
that we would for AX.25 callsigns, then we get the byte sequence

4F 53 43 35 34 36 then "C0" then 47 53 58 37 34 39 then "10" then "03" 
then "F0"

and translating just the "callsigns" back to ASCII we get
O S C 5 4 6 "C0" G S X 7 4 9 "10" "03" "F0"

and then treating this like an AX.25 frame we would end up with "C0" and 
"10" as
SSID values "0" and "8" per the CRRSSID0 format. This gives us the 
OSC546 with SSID 0 as the destination callsign and GSX749-8 as the 
station. Not valid amateur radio callsigns, but...

"03" would be the AX.25 control byte corresponding to "Unnumbered Frame"
(U frame) [footnote 4]


"F0" is the protocol identifier byte (PID) indicating that there is no 
layer 3 protocol
implemented. [footnote 5]

Depending on your TNC model, the output from a TNC in non-KISS mode would
look something like this:

2014-01-21 17:56:35.490 UTC
GSX749-8*>OSC546:<UI>:This is another Trailblazer Repeater test

Hope this helps.

Douglas KA2UPW/5

[1] Hex dump from Ken's email, but this might not be correct if the 
ASCII characters were corrupted by the mailing list. In particular the 
letter of each callsign might be some other value. Also, since I did all
of this by hand, there a chance I made mistakes. The actual hex dump of
the received packet would be much more conclusive.

[2] The KISS TNC: A simple Host-to-TNC communications protocol.
Section 2. http://www.ka9q.net/papers/kiss.html

[3] deleted

[4] AX.25 Link Access Protocol for Amateur Packet Radio Version 2.2.
Page 26. Section 4.2.1. http://www.tapr.org/pdf/AX25.2.2.pdf‎

[5] AX.25 Link Access Protocol for Amateur Packet Radio Version 2.2.
Page 7. Figure 3.2. http://www.tapr.org/pdf/AX25.2.2.pdf‎

On 1/21/2014 12:08 PM, Ken Swaggart wrote:
> During FO-29 passes near the USA west coast I've noticed a 9600 baud 
> data signal in the downlink. Today I finally got a decode and the 
> OnLineKissPlus file shows:
> À 2014-01-21 17:56:35.490 UTCÀÀž¦†jhlÛÜŽ¦°nhr ðThis is another 
> Trailblazer Repeater test`
> The uplink would be about 145.945 MHz.
> Anyone have an ID?
> 73,
> Ken, W7KKE
> CN75xa

More information about the AMSAT-BB mailing list