MFSK16

MFSK Applications

When to Use MFSK16

The strengths of an MFSK mode with FEC lie in is robustness and reliability under poor conditions. This mode was developed to enable those skeds to be kept, no matter what the conditions prevailing. MFSK is neither fast nor error free - just reliable and robust. For fast error-free activity an ARQ mode such as Pactor should be used, but do not expect the same performance in poor conditions.

MFSK16 is a keyboard-to-keyboard "real time" mode, suitable for rag-chewing, nets and DX. Since the error correction is of the FEC type, it is also highly appropriate for bulletin broadcasts. Its technical superiority and ease of use should make it a natural replacement for RTTY, and should be considered for other rag-chew activity as well. Use MFSK when conditions are very changeable, the band is dying, or there is excessive ionospheric doppler. Use MFSK on low bands when you want good copy despite very bad static and lightning noise.

At some point in the future an ARQ version of MFSK16 for BBS use may be developed. This could have automatic mode change and power level change to take advantage of improved path conditions.

Where to Use MFSK16

MFSK16 is a digital mode, and an FSK mode. Use it at the lower end of the digital allocation on each Amateur band, where RTTY operation normally takes place, for example at around 14.080 MHz on the 20m band. Be careful if the band is busy with other signals. Use the waterfall display to find a gap about 250 - 500 Hz wide, and fit your signal in. The MFSK signal is typically 350 Hz wide - narrower than many other digital signals.

MFSK is sideband dependent, so the signal MUST be transmitted using the correct sideband. All MFSK operation is on USB above 10 MHz, and LSB below 10 MHz. In this document frequencies are quoted as the Idle Carrier Frequency (the lowest audio tone).

LF
Use MFSK16 on the LF bands - the US "Lowfer" band, the European and Australasian 136 and 180 kHz bands. For the ultimate DX weak signal performance, use the lowest baud rates and modest number of tones, for example 3.9 baud 8 tones. Typing speed will be SLOW. Narrow receiver filters are not necessary. FEC at these baud rates will cause very long delays, which will not be important when used for beacon purposes, but will make QSOs a trial of patience.

MF
MFSK16 copes very well with power noise and lightning noise on MF. Night-time performance on 160m and 80m is very good - 10W power should give good copy at modest typing speeds over a 3000 km range. Use 7.8 baud, 32 tones for example, without FEC. This gives about 40 WPM! Daytime range will be sensitivity limited, and PSK31 may be more appropriate if noise is low and signals are weak, but stick with MFSK if it's noisy.

The calling frequency in the South Pacific is 3.545 MHz idle carrier. It can also be heard in ZL and VK on 3.559 MHz.

HF
On the upper HF bands, MFSK16 is no better than PSK31 for normal QSOs, skeds and so on, especially when conditions are good. When conditions are poor however, or there is bad polar flutter on the intended path (long path for example), an MFSK mode is much better. 7.8 baud 16 tone or 15.625 baud 16 tone offer excellent performance. QRM will be less of a problem than with PSK31.

MFSK really shines on 30, 20, and 17 metre bands. On the higher bands, 15, 12m and 10m, PSK31 or STREAM will probably be more appropriate for long distance contacts. The 17m calling frequency is 18.106 MHz idle carrier. 14.080 MHz is suggested for 20 metres.

VHF/UHF
It would be more appropriate to use PSK31 for DX on VHF. If drift is a problem, use PSK-Hell, STREAM or Feld-Hell, which is especially good with extreme drift such as satellite doppler shift. An MFSK mode, especially with a very slow baud rate, would be excellent for moonbounce, due to immunity from phase errors (libration).

How MFSK16 is Defined

The technical designation of radio modes is defined by the CCIR, and nowhere more succinctly explained than in the FCC Part 47 Rules, paragraph 2.201. From this information we see that MFSK16 is a multi-frequency, single channel, FSK telegraphy transmission mode. The CCIR designation is therefore F1B (or F1D if transmitting non-text data).

The definitions make no distinction between single-carrier and multi-carrier single channel systems, so MFSK and RTTY are equivalent. After all, RTTY is in reality 2FSK.

Transmission Bandwidth

Necessary bandwidth is also defined by CCIR, and the process explained well in FCC Part 47, paragraph 2.202. For a telegraph signal the necessary bandwidth is defined as:

BW = 2M +2D.K

Where M is the maximum modulating frequency and D is the peak deviation. K is a factor related to the keying technique. K=1.2 for hard keyed FSK.

For an MFSK system this formula can be restated as:

BW = B +m.s.K

where B is the baud rate, m is the number of tones, and s is the tone spacing. For example, for a 16 tone, 15.625 baud system with 15.625 Hz tone spacing (the MFSK16 default mode), the bandwidth is:

BW = B +m.s.K = 15.625 + 16 x 15.625 x 1.2 = 315.625 Hz.

Thus the overall designation of the default MFSK16 mode is 316HF1B.

As a comparison, 170 Hz shift 50 baud RTTY is 254HF1B. In practice most RTTY signals heard on Amateur bands are rather wider than this! Due to the way MFSK16 is generated, it will be very difficult to create a wider signal by overdriving the transmitter, although excessive audio level can cause audio harmonics to occur that cannot be the fault of the transmitter or system design.

MFSK16 Software

MFSK16 was envisaged as an open source, open specification mode. As such, the intention is that any competent developer can create a version for a preferred hardware platform. So far, all work has been for Windows 95/98 and the SoundBlaster 16 sound card, on a Pentium Class computer. There is also interest in a Linux version.

It is to be hoped that within the forseeable future, MFSK16 will be available for:

For this to be possible, the full specification, the algorithms and the crucial source code will need to be released into the public domain. This should happen over the next few months as the technical details are finalised. These documents will be released on this web site, probably in PDF and text file formats.

Where do I get MFSK16 Software?

At present the public release must wait until testing is complete. This will ensure that the software performs as expected, and that it is easy to use without requiring a degree in rocket science. The last effort to finalize everything, complete documentation and so on will take a few weeks yet.

Technical experts and experienced digi-operators are at present testing the development software in order to check for problems and familiarise themselves with the mode. If you have the technical capability, the time, and the interest to take part in the test program, send an email to MFSK-subscribe@egroups.com. This will automatically subscribe you to the tester's email reflector.

Software for testers is available from the Documents Page. This test software by Nino IZ8BLY is called "STREAM", and also includes Nino's super-PSK mode, PSK63F.

Further information will be added to this web site as it becomes available. The release software will be posted here as soon as possible, and the MFSK, HFSIG, Hellschreiber, PSK31 and MT63 Reflectors will be informed. Release will possibly be as early as mid August.

MFSK16 Home Page