January 27th 2008

Mode to try: QPSK31

Description
===========

QPSK31 is very similar to regular PSK31 (actually called BPSK31).
The difference is that it uses a quadrature PSK modulation (4
states) rather than a binary PSK modulation (2 states). In theory
it should provide more reliable reception because of the extra
states employed in an error correcting fashion. On the downside,
it requires more critical tuning but as this is handled by the
software you use it's not something to worry about.

Specifications
==============

MultiPSK's help pages say this about QPSK31....

Baud rate       : 31.25
Speed           : 37 wpm in capital letters and 51 wpm in small
                  letters (average)
Receive mode    : USB
Bandwidth       : about 80 Hz,
Demodulation 	: coherent,
Synchronization : automatic using the signal
Correction code : no
Convolution code: Yes for QPSK31 (Rate=1/2, Constraint length=5,
                  use of Viterbi decoder with soft decison)
Interleaving 	: no
AFC             : about +/- 10 Hz depending on signal-to-noise
                  ratio
Drift tolerance : 20 Hz/min in QPSK31 (depending on level)
Pmean/Ppeak     : 0.35 for QPSK31
Lowest S/N      : -11.5 dB

Operating guide
===============

Basically use QPSK31 just as you would regular PSK31. The only
real thing to make sure of is that your rig is in USB mode. If
not, your sigs will be "upside-down" just as in RTTY. Tuning may
be a little more demanding but this should be handled by your
software.

Recommended Frequencies
=======================

Just like PSK31 the primary area on 30m is around 10.140 MHz (VFO)
in USB.

Try to avoid placing your signal on a carrier frequency of
10.141 MHz (i.e., 10.140 MHz + 1000Hz AF) as this is the PropNet
beacon frequency. You should also try to avoid transmitting over
the top of the QRPP folks who hang out over a 200Hz range starting
at 10.140 MHz carrier frequency (i.e., 10.139 MHz + 1000Hz - 1200Hz)

I would recommend setting your VFO to 10.140.15 MHz USB and you should
be just fine!

Availability
============

Just about every multi-mode program out there has
the QPSK31 mode.

Some recommended Windows software to try:

Digipan     http://www.digipan.net/
MultiPSK    http://f6cte.free.fr/
DM780       http://hrd.ham-radio.ch/DM780/DM780.htm
MixW        http://www.mixw.net/

And for Linux, you could try

FLDigi      http://www.w1hkj.com/Fldigi.html

For Mac there is only MultiMode (to my knowledge) it is available
at http://www.blackcatsystems.com/software/multimode.html

On the 27th I will configure my autospotter software to report
QPSK transmissions so you should be able to see yourself on the
spot page at http://www.projectsandparts.com/30m/

Sound Sample
============

As QPSK31 sounds identical to regular PSK31 I haven't provided a
sound sample this month. I will start this in February when we
look at MFSK16.


73 es GL!
Sholto, KE7HPV
Republic, WA.

Comments or errata to: KE7HPV