PSK-31 is a sound card mode which has re-instilled in many hams a new excitement in HF radio. It has been around for a few years, and in the last 18 months the usage has exploded. Many articles in QST, hams spreading the word about this mode, and ease of getting started have driven this explosive growth.

PSK-31 uses the PC CPU, software and sound card interface to provide all modulate / demodulate functions as well as operator interface and control. The sound card is attached to an HF SSB rig using the PC speaker out and microphone in ports on the sound card. Typically, there is an interface installed between the sound card and the rig to adjust signal levels and provide good isolation between the two devices. On the SSB rig side, typically the microphone input and external speaker out are used. PTT control is done via a control signal on a PC serial port (RTS or DTR) and isolated with an opto isolator to drive the rig PTT line. In some cases, the accessory port of the rig can be used in lieu of the microphone and external speaker ports.

Advantages of PSK-31 are:

  - A very effective low power communication mode - most rigs are < 50w

  - Extremely efficient of band width used - 31 Hz wide signal, separation of as little as

    100 Hz is normal

 - Data rates are consistent with that of a fast typist, variable length encoding is used

   to raise the effective data rate above the 31 baud level

 - Upper and lower case characters and backspace are supported

 - Easy to use, many good free software packages available

 - Lots of activity, used widely throughout the world

 - Good dx mode (except for over the pole contacts - see below)

 - All HF bands 80 - 10m can be used, although 20m is by far the most popular

Disadvantages

 - No error correction is used, so contacts involving phase distortion can render the mode

   much less effective. This occurs often in contacts over the pole with polar flutter. In

   all other cases, the mode is reasonable resistant to other forms of noise or distortion

Where to get software and information:

 - Digipan software: available free from http://www.digipan.net/

 - Hamscope software: available free from http://www.qsl.net/hamscope/

Some websites and reflectors available for PSK31 mode

 - http://kk7uq.hfradio.org/index.htm Sound card interface design

 - http://www.psk31.com/ A good general information site

 - http://groups.yahoo.com/group/psk31 PSK31 Reflector

 - http://aintel.bi.ehu.es/psk31.html The "official" psk31 website

MFSK-16 is a sound card mode which has been introduced as an alternative to PSK-31 for long haul dx and over the pole communications. An article by ZL1BPU in QST a year ago has driven much interest in this mode, although it is not as popular as PSK-31 in overall usage.

MFSK-16 uses frequency modulation instead of phase modulation, and as a result is much less susceptible to errors caused by phase distorting multi-hop and over the pole communications. Forward error correction is also a feature of this mode which enhances reliable communication in low signal level or noisy conditions.

Like PSK-31, MFSK16 uses the PC CPU, software and sound card interface to provide all modulate / demodulate functions as well as operator interface and control. The sound card is attached to an HF SSB rig using the PC speaker out and microphone in ports on the sound card. Typically, an interface used for PSK-31 will work with the MFSK-16 mode.

Advantages of MFSK-16 are:

- A very effective low power communication mode - most rigs are < 50w

- Efficient of band width used - 250 Hz wide signal, separation of as little as

  300 Hz is acceptable

- Data rates are consistent with that of a fast typist, variable length encoding is used

  to raise the effective data rate

- Upper and lower case characters and backspace are supported

- Good free software packages available

- Fairly good 20m activity, used widely throughout the world

- Very good dx mode

- All HF bands 80 - 10m can be used, although 20m is by far the most popular

Disadvantages

- Wider signal than PSK-31 (250 Hz vs 31 Hz)

- Buffered FEC functions provide a delay in startup of an ‘over’, so is not a

  good contest mode, but is an excellent ragchew mode

- A little harder to tune than PSK-31, requires better frequency stability

Where to get software and information:

- Hamscope software: available free at  http://www.qsl.net/hamscope/

- Stream software: available free at  http://iz8bly.sysonline.it/

Some websites and reflectors available for MFSK-16 mode

- http://kk7uq.hfradio.org/index.htm  Sound card interface design

- http://groups.yahoo.com/group/MFSK    MFSK16 Reflector

The concept of using the PC Sound Card as the audio source for digital modes has also been effectively applied to RTTY. An excellent software program has been provided, free of charge, by Makoto Mori, JE3HHT.

Like PSK-31, and MFSK16, the MMTTY version of RTTY uses the PC CPU, software and sound card interface to provide all modulate / demodulate functions as well as operator interface and control. The sound card is attached to an HF SSB rig using the PC speaker out and microphone in ports on the sound card. Typically, an interface used for PSK-31 will work with the MMTTY. Because the frequency shift is controlled by the software, new types of RTTY are being tried - including the 23 baud RTTY mode which occupies much less bandwidth than normal RTTY.

The MMTTY implementation is available from JE3HHT, and the ‘engine’ has been licensed to other software providers such as Hamscope and Zakanaka.

Advantages of MMTTY are:

- An excellent implementation of RTTY, using the sound card and PC.

- Compatible with RTTY using conventional methods

Disadvantages

- Wider signal than PSK-31 (250 Hz vs 31 Hz), and greater separation required than

  MFSK16

- Error rates higher than MFSK-16 for comparable power

- Upper case only, no backspace supported

Where to get software and information:

- MMTTY software http://www.qsl.net/mmhamsoft

- Hamscope software: available free from http://www.qsl.net/hamscope/

- Zakanaka software: http://www.qsl.net/kc4elo

Some websites and reflectors available for MMTTY mode

http://kk7uq.hfradio.org/index.htm   Sound card interface design

http://groups.yahoo.com/group/MMTTY        MMTTY Reflector

The concept of using the PC Sound Card as the audio source for digital modes has also been effectively applied to Slow Scan TV. An excellent software program has been provided, free of charge, by Makoto Mori, JE3HHT, who also provided the MMTTY program.

Like the other sound card modes, MM-SSTV uses the PC CPU, software and sound card interface to provide all modulate / demodulate functions as well as operator interface and control. The sound card is attached to an HF SSB rig using the PC speaker out and microphone in ports on the sound card. Typically, an interface used for PSK-31 will work with the MMTTY.

Advantages of MM-SSTV are:

- An easy to use software package for SSTV.

- Compatible with other methods of implementing SSTV

Disadvantages

- Since the common method of starting a SSTV QSO is to use SSB, some method of

  switching between microphone and the sound card interface must be implemented

Where to get software and information:

- MM-SSTV software http://www.qsl.net/mmhamsoft

Some websites and reflectors available for MM-SSTV mode

- http://kk7uq.hfradio.org/index.htm Sound card interface design

- http://groups.yahoo.com/group/MM-SSTV MMSSTV Reflector