
April 1, 1995 @ 10:00 CST

Hi gang,

Here are the updated psk modems for the microsats:

packing list:

      psk93r1j.*       port 1, psk modem for microsats
      psk93r2j.*       port 2, psk modem for microsats

LEDs:

      1                 Smart Tune
      2                 PTT

      3                 DCD (pll locked with low phase error)
      4                 tuning pulses

      5                 NOT_DCD
      6                 level

      7                 Duty Cycle
      8                 Power

The 900 MHz Butterworth filters used before have been replaced with 660 Hz 
Bessel filters. This has improved the performance of the modem noticeably 
at my QTH. Live DCD has also been added via a lock detector on the Costas
loop detector.

LED 5 is in "parallel" with the low true DCD line to the modem disconnect, 
and goes off (low) when DCD is asserted. LED 3 is the inverse of LED 5; it 
goes on when DCD is asserted. The DCD action sort of jumps between 
these two LEDs. The PTT LED operation was borrowed from W5RKN.

This update also adds modem reset via sending an "r" or "R" character to 
the modem through the DSP-93 UART. 

Notes:

1. For satellite operation and loopback testing, set your TNC to FULLDUP.

2. The TNC DCD light on my UNMODIFIED MFJ1270C does not light with DSP-93
DCD assertion, but the TNC software does correctly hold off the transmitter. 
(The DCD light on the MFJ1270C is operated directly by the on board modem for
some reason - thanks to W5RKN for this observation.) I believe Mark Hammond
KC4EBR has developed a mod for the MFJ1270C that operates its DCD light in
sympathy with the DSP-93.

3. The values of CNTH and CNTL are set for my ICOM 475H. The 475 tunes in 
50 Hz steps. These values may have to be adjusted for other radios. CNTH 
sets the time from the start of one tuning pulse to the next tuning pulse,
and CNTL sets the width of the pulse. Current values are CNTH = 288 and 
CNTL = 186. Try reducing these values (proportionately) to increase the 
tuning rate if the tuning doesn't keep up on a high pass with heavy doppler 
shift.

4. License and Disclaimer

 A no cost, non-exclusive license to use the enclosed software is granted
 to all users of the TAPR/AMSAT DSP-93 DSP computer, with the restriction
 that it be used only for non-commercial amateur radio applications. ALL
 other uses are prohibited under this license. Copyright 1991, 1992, 1993
 and 1994, 1995 Frank H. Perkins, Jr., WB5IPM. All rights reserved.

 This software is EXPERIMENTAL. It is offered AS IS, without Warranty or
 Guarantee of any kind. NO representation is made that this software is
 suitable for any purpose, or that its operation is reliable. Use this software
 strictly at your own risk. The author, AMSAT and TAPR accept no liability
 for any loss or injury arising directly or indirectly from its use.

 Never use this software under circumstances where its failure to operate
 or its failure to operate as expected, or the failure of the attendant
 hardware could create a dangerous situation, cause loss of data, or could
 cause damage to your amateur radio equipment, computer equipment, or
 any other equipment or property.

 Please contact Greg Jones at TAPR or the author for information on
 commercial licenses of this software.

 Frank H. Perkins, Jr.

73, Frank WB5IPM
