[aprssig] APRS tone encode question

[scott at opentrac.org]

Yeah, I'd expect 16 levels.  Haven't had a chance to look at my TT3 to see
what it's actually doing.

Here's a snapshot of an OpenTracker's output.  Steps aren't really visible
on this 'scope...

http://n1vg.net/opentracker/images/waveform.jpg

The OpenTracker uses PWM for D/A.  In AFSK mode it uses 4 bits resolution,
and in BPSK mode it's 8.  Works pretty well.  I'll have to do a comparison
of the output waveforms of the TT3, OpenTracker, and MX614 sometime.  For
audio stuff, Yoshimasa Electronic's RAL package is great.  It's got a nice
oscilloscope and FFT analyzer display, plus a signal generator and assorted
other features.

Scott
N1VG

-----Original Message-----
From: aprssig-bounces at lists.tapr.org
[mailto:aprssig-bounces at lists.tapr.org]On Behalf Of Andrew Rich
Sent: Monday, August 23, 2004 2:40 AM
To: TAPR APRS Special Interest Group; TAPR PIC Development Special
Interest Group
Subject: [aprssig] APRS tone encode question


I threw the tinytrak audio onto a CRO and compared it to a sine wave from a
sig gen.

How come a DAC ladder network of 4 resistors only produces 8 steps ?

Should it not end up being 16 steps ?

0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111

image

http://www.tech-software.net/139_3935.JPG


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