To:      QRSS Knights and Friends
From:    Joe Taylor, K1JT
Subject: New software for MEPT
Date:    March 13, 2008

About two weeks ago Murray Greenman, ZL1BPU, wrote to me suggesting
that I consider adding a mode optimized for MEPT to my software
package WSJT.  I expressed interest in the idea, and we exchanged a
few emails about possible specifications.  Then I sat down and wrote
out some detailed specs, and finally got busy to write a bare-bones
program implementing the new mode.

I write now to let you know that an early release of the program is
ready for testing.  The program's name is WSPR (pronounced "whisper",
which seems appropriate for estremely weak signals).  The name of the
digital protocol implemented in WSPR is MEPT_JT, where the letters
stand for "Manned Experimental Propagation Tests, by K1JT".

At present WSPR is a stand-alone executable, independent of WSJT.  It
is functional for both transmitting and receiving, but it has no
frills -- no graphics, no GUI, etc.  It is executed from a Windows
command prompt.  Like WSJT, WSPR uses a computer sound card to
generate audio tones to modulate an SSB transceiver operating on upper
sideband.  In receive mode the sound card digitizes audio from the
transceiver.  The program scans a 200 Hz passband (the "QRSS window")
looking for MEPT_JT signals, and decodes them.  Basic operating
instructions for the initial release can be found in the file
WSPR_Instructions.TXT at
http://physics.princeton.edu/pulsar/K1JT/WSPR_Instructions.TXT , and
the program itself can be downloaded from
http://physics.princeton.edu/pulsar/K1JT/WSPR.EXE .


Basic specifications of the MEPT_JT mode are as follows:

1.  Transmitted message: callsign + 4-character-locator + dBm 
    Example: "K1JT FN20 30"

2.  Message length after lossless compression: 28 bits for callsign,
    15 for locator, 7 for power level ==> 50 bits total.

3.  Forward error correction (FEC): long-constraint convolutional 
    code, K=32, r=1/2.

4.  Number of channel symbols: nsym = (50+K-1)*2 = 162.

5.  Keying rate: 12000/8192 = 1.46 baud.  

6.  Modulation: continuous phase 4-FSK.  Tone separation 1.46 Hz.

7.  Synchronization: 162-bit pseudo-random sync vector.

8.  Data structure: each channel symbol conveys one sync bit and one
    data bit.

9.  Duration of transmission: 162*8192/12000 = 110.6 s.  

10. Transmissions start two seconds into an even UTC minute: i.e., at
    hh:00:02, hh:02:02, ...

10. Occupied bandwidth: about 6 Hz

11. Minimum S/N for reception: around -27 dB on the WSJT scale (2500
    Hz reference bandwidth).  

You can run Argo, Spectran, or WSJT at the same time as WSPR, in
order to provide a waterfall spectral display.

In normal operation WSPR displays information every two minutes and
is silent otherwise.  In transmit mode in prints a single line when a
new transmission starts.  In receive mode the program looks for all
detectable MEPT_JT signals in a 200 Hz passband, decodes them, and
displays the results.  If nothing is decoded, nothing will be printed.
In T/R mode the program alternates in a randomized way between
transmit and receive sequences.

Like JT65, MEPT_JT includes very efficient data compression and strong
forward error correction.  Received messages are nearly always exactly
the same as the transmitted message, or else they are left blank.

Version 0.3 of MEPT_JT is functional -- and extremely sensitive -- but
the user interface is rather spartan.  Suggestions for improvements
will be most welcome!

Please email all suggestions to k1jt at arrl dot net.

	    -- 73, Joe, K1JT