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[aprssig] APRS tone encode question

Andrew Rich vk4tec at tech-software.net
Tue Aug 24 08:58:26 UTC 2004


Does Packet require the tone shift from 1200 to 2200 to occur at a zero
crossing ?
  -----Original Message-----
  From: aprssig-bounces at lists.tapr.org
[mailto:aprssig-bounces at lists.tapr.org]On Behalf Of scott at opentrac.org
  Sent: Tuesday, 24 August 2004 4:50 PM
  To: 'TAPR APRS Mailing List'
  Subject: RE: [aprssig] APRS tone encode question


  I do all of my schematics and board layouts in Eagle PCB, by Cadsoft.  The
library system is awful, but I've gotten used to it, and it's a good program
overall.  Hard to beat what it does for the price.

  I find it's often quicker to sketch out a schematic, generate a board
layout, and etch and drill the board than it would be to build the same
circuit on a protoboard.  I just did one today that worked right on the
first try, despite me reversing the top and bottom layers.  It's a small
board (2.5" by 3") that serves as a carrier for a surface mount OpenTracker,
and provides APP power connectors (in and out), a power MOSFET for radio
power control, radio connector, serial connector, and RJ11 connector for a
1-wire weather station.  The firmware needs some debugging, but it makes for
a very compact, low-power (8 ma @ 12 volts) weather station.  (Power
consumption is down to about 4 ma for some test boards and firmware, but it
still needs work.)

  Scott
  N1VG
    -----Original Message-----
    From: aprssig-bounces at lists.tapr.org
[mailto:aprssig-bounces at lists.tapr.org]On Behalf Of Marsh Jas III
    Sent: Monday, August 23, 2004 8:38 PM
    To: TAPR APRS Mailing List
    Subject: RE: [aprssig] APRS tone encode question


    Hi Scott:

    What program program did you  use to make your schematic? It looks neat.

    Tnx.

    Jim.  w9nje

    scott at opentrac.org wrote:
      The schematic is here: http://n1vg.net/opentracker/ot1_schematic.png.
The
      PWM waveform comes from pin 13 (timer channel 0) of the MCU. The
output is
      a 57.6 KHz square wave with the duty cycle determined by the sine wave
      lookup table. The PWM frequency and its harmonics are far enough out
of the
      audio passband to not be a problem.

      Scott
      N1VG

      -----Original Message-----
      From: Andrew Rich [mailto:vk4tec at tech-software.net]
      Sent: Monday, August 23, 2004 1:46 PM
      To: scott at opentrac.org; 'TAPR APRS Mailing List'; 'TAPR PIC
Development
      Special Interest Group'
      Subject: RE: [aprssig] APRS tone encode question


      Scott how do you get this waveform ? RC ?


      -----Original Message-----
      From: Scott Miller [mailto:scott at 3xf.com]On Behalf Of
scott at opentrac.org
      Sent: Tuesday, 24 August 2004 4:17 AM
      To: vk4tec at tech-software.net; 'TAPR APRS Mailing List'; 'TAPR PIC
      Development Special Interest Group'
      Subject: RE: [aprssig] APRS tone encode question


      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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