PSK 31
PSK31 is a fun mode of operation.  I first got into PSK in May of 2001 and have enjoyed operating it since.  I had operated a little RTTY and AMTOR back in 1994 using a Kantronics all-mode TNC, but lost interest after a while.  However, when I got interested in QRP I learned about the PSK31 mode and its low-power capabilities, and soon regained my interest in digital HF keyboard-to-keyboard operation.  Basically what PSK31 is is a Phase-Shift-Keyed 31 Hz wide signal.  The narrow bandwidth of the signal makes it good for low-power work since the signal will be more easily read by the DSP function of the decoding software.  The mode supports a full character set giving upper and lowercase letters and punctuation.  This is contrasted to standard RTTY which only allows for uppercase characters due to its five-bit coding system.  PSK31 is sent at 31.25 baud which works out to 50 WPM. 

At first I had planned to buy & build a Warbler PSK transceiver kit, but soon found plans for a PSK31 interface on the internet.  I decided to build the interface to use with my Kenwood TS-140 so that I wouldn't be stuck on just one band as I would have been with the Warbler kit.  Plus I could run higher power than 5 watts if I wanted to.  I quickly built the interface from scratch and was on the air.

The program I use for PSK31 is MultiPSK.  It is a free, but full-featured program that not only sends & receives PSK31 with a sound card, but a whole host of modes including multiple PSK modes, RTTY, SSTV, MFSK, Packet, as well as many other digital modes.

MultiPSK also has the ability to set up macros, or blocks of text that you can send by clicking a button.  You can set up the macros to be anything you want, from CQ announcements to your station's equipment setup.  The macros make it easier to send information that you would otherwise have to type in.  PSK31 is sent at 31.25 baud which works out to 50 WPM, so it's handy to have macros to send.  Even fast typists will have the transmit buffer occasionally catch up to them.  One operating habit I've gotten into is to type my reply to the station I'm in QSO with when they are transmitting.  When it's time for my over I press the transmit button and let the text in the buffer transmit and finish typing.

Since PSK is an excellent low-power mode, I normally operate with a power level of no more than 20 watts.  There really isn't any reason to use 100 watts when operating PSK.

The HF PSK frequencies are as follows:
160 meters - 1.807
80 meters - 3.580
40 meters - 7.070
30 meters - 10.140
20 meters - 14.070
15 meters - 21.070
10 meters - 28.120

Frequencies are usually tuned in USB mode, so the actual operating frequencies will range from the base freq to 3 kHz up.  What this means is that you can fit dozens of 31 Hz-wide PSK signals into the same bandwidth of one SSB signal.
Links
www.packetradio.com   Despite its name, has a ton of information about PSK operating, plus has schematics for building your own PSK interface.
Small Wonder Labs Warbler   A neat 5 watt PSK transceiver kit.
AC6V's website has various PSK software programs available for download.
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