[aprssig] Expanded APRS telemetry to 10 or 15 channels?

Robert Bruninga bruninga at usna.edu
Thu Apr 2 14:37:05 EDT 2020

Expanding APRS telemetry from 5 to ten, 15 or 20 channels and still
remaining within the protocol...

On PSAT3, I needed 6 A/D inputs instead of the standard 5, so I used two
inputs on channel 2.  If the count is above 500 then it means one thing,
and if it is below 500 it means another.  On receipt, I can choose one
telemetry equation or the other depending on the value above or below 500.

This means you could double the 5 channels to 10 if you used 500 as the
dividing line.  Or you could have 15 channels if you restricted one input
from 0 to 333 and the next between 333 and 666 and the last between 666 and
999.  You can make the transition points be anything that matches the
resolution of your sensors, because the thresholds would be part of the
decoding equation.  Even if you used four ranges, your precision (from
0-250) is still better than a half percent!

Wow, I wish I had thought of this on my earlier PSATs. Having ten or 15
channels of A/D telemetry while still using the standard APRS protocol
would have been useful.

On the sensor side, you simply switch in bias resistors on each of the two,
three, or four sensors per input channel.  Think of it as bank switching
the 5 channels...

If anyone has use for this trick, let me know.  Steve Dimse is looking at
building it into FINDU for trivial plotting... if/when he finds he time...

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