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1993-12-31
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DSK-MODEM V1.00
DSK-MODEM (c) Johan Forrer KC7WW 1993,1994
Author: Johan B. Forrer KC7WW
26553 Priceview Drive
Monroe, OR 97456
United States of America
CIS id: 70730,3472
Shareware notice
This program is distributed as a Shareware product. You may
freely copy and share the program with your friends, associates
and other radio amateurs. DSK-MODEM is a collection HF digital
modems using the finest DSP algorithms, all written in hand-
crafted DSP assembly language that delivers uncompromising
performance. This program is intended to be used with the
author's companion programs, PCTOR, and PC-PACTOR. Compatibility
with other programs is not guaranteed. DSK-MODEM may not be sold
or distributed with another product without the express written
permission of the author. The author, Johan Forrer, KC7WW will
only support unmodified copies of this software.
If you decide to use this product, you should become a registered
user by sending $15 or equivalent in foreign currency together
with the completed registration form to the author. All
transactions must be drawn on US banks. Upon receipt of your
registration, you will receive one free update disk containing
the latest release of the software. You will also be notified of
future developments.
If you are not satisfied with the program after registering it,
you have 30 days from your registration date to return it for a
full refund of your money, no questions asked.
Previously registered users may obtain a free upgrade to this
version - please send a formatted disk and SASE (or stamped
mailer or 2 IRC's).
This program may not be used by business or government
institutions without proper licensing. Commercial users please
contact Johan Forrer directly for modifications and/or details of
site licensing.
CONTENTS
1. Requirements
2. DSP modem background.
3. RS 232 connections.
4. Special modems
5. Disclaimer
1.0 Requirements
DSK-MODEM downloads DSP code to a TI 320C26 DSK target. In its
simplest form, the supplied DSP modems will work on an unmodified
DSK unit. It is, however recommended to add the included
interface circuit for effective tuning display and full transmit
capabilities.
PCTOR version 3.02C or higher is required. Please contact the
author if operation with other software tnc's is required.
1. DSP modem background
The TI 320C26 digital signal processor starter's kit (DSK) is
used as a platform for implementing a number of DSP modems. For
those not too familiar with this little unit, the DSK is a 2" x
3" PCB containing a 40MHz DSP and associated circuitry. The DSK
module is available from TI distributors as part no. TMDS3200026,
and costs only $99. Please note that the schematic for a simple
interface containing a tuning display and PTT driver is included
as a separate plot file in this package.
IMPORTANT NOTE: Soldering on the DSK PCB will void your
warrantee. The author is not liable in any way for damages that
may result in such modifications. Also please note that there is
a minor hardware fault on the DSK PCB. A simple fix for this
fault is described in the TI DSK newsletter. The fault amounts to
a missing trace that connects a resistor SIP package to VCC.
Without this trace, external interfaces will not work properly.
The DSK connects to a PC computer's COM port and communicates
with the PC at 115200 baud. DSK-MODEM contains all the code
necessary to communicate with the DSK. Once a particular modem is
selected, DSP code is downloaded silently to the DSK's on-chip
memory. This operation only takes a second or so to complete. The
DSP then performs all signal processing operations in real time
using its 10 MIPS engine. The resulting output from the DSP is a
stream of data bits that is sent to the PC for further processing
by programs such as PCTOR or PC-PACTOR.
In addition to the RS 232 connection, an audio signal from your
transceiver is fed to the DSK's analog to digital convertor. If
PCTOR is to be used to transmit data over the air, additional
wiring to the transceiver PTT and FSK control is also required.
All the DSP modems used in this package uses non-coherent
detection principles to recover digital signals. The operation
may be summarized as follows:
The audio signal is first digitized by an A/D convertor and then
applied to two parallel discriminator filters. The envelopes of
the outputs of the discriminator filters rectified and then
low-pass filtered. The output of the low pass filter are
thresholded and the corresponding 0/1 output applied to the TxD
serial line (the FLAG output of the 320C26). In addition, the
output of the low pass filter is written to a D/A convertor. This
signal is useful as a tuning aid when an oscilloscope is used.
Just tune for maximum positive to negative transitions.
2. RS232 Connections
For a minimal interface, Rd, Td, DTR, RTS, DCD, and Ground, is
required. This will allow operation on RTTY and AMTOR.
For a 25-pin serial connector:
pin 2 (TD) - output data bits (mark -12V, space +12V)
pin 3 (RD) - input data (also connected to pin 8 (DCD))
pin 4 (RTS) - PTT (off -12V, on +12V)
pin 8 (DCD) - input data bits (mark -12V, space +12V)
pin 7 (Ground)
For a 9-pin serial connector:
pin 3 (TD) - output data bits (mark -12V, space +12V)
pin 2 (RD) - input data (also connected to pin 1 (DCD))
pin 7 (RTS) - PTT (off -12V, on +12V)
pin 1 (DCD) - input data bits (mark -12V, space +12V)
pin 5 (Ground)
If this program is to be used with the popular BAYCOM packet
program, an additional wire link between RD and CTS is needed.
3.0 Special modems
Four modems are provided for usage on RTTY, AMTOR, PacTOR, and HF
Packet. The main features are summarized in the following table
Tone freq's BW Data LPF
--------------------------------------------
RTTY 2125/2295 85 50
AMTOR 2125/2295 100 100
PacTOR 2110/2310 160 100
HF Packet 1600/1800 160 150
--------------------------------------------
4.0 Disclaimer
The author, Johan Forrer KC7WW is not responsible for any damage,
injury, loss of profit or gain associated with the use,
installation, or application of this software.
December 1993
J.B.Forrer KC7WW
26553 Priceview Drive
Monroe, OR 97456
United States of America