ZL2AFP DominoEX HELP

This is a computer program for Amateur Radio transmission and reception using a computer and HF radio transceiver. The program provides computer chat-mode operation on the HF bands, using a sound card technique to generate and modulate for transmission using tones at audio frequency, and receive and decode the incoming signals, also at audio frequency. An SSB transceiver translates these signals to and from the HF Amateur Bands. The DominoEX mode is a development from earlier experimental DominoF and DominoG programs, but is not compatible with them. This version (DominoEXFEC V2.0) is compatible with earlier ZL2AFP DominoEX versions, and also with MULTIPSK, with and without FEC.

DominoEX operates using a variation of the MFSK technique (MFSK = Multiple Frequency Shift Keying), since MFSK offers very good immunity to interference and ionospheric effects, and is also very sensitive. However, MFSK can be quite difficult to tune in, and suffers from some interference effects, which are usually masked by using error correction. This unique program addresses these limitations in a special way that wipes away all problems. DominoEX is easy to use, and hence ideal for beginners. You will be impressed with the performance!

MFSK is a respected and mature technique, a generalized form of FSK (FSK = Frequency Shift Keying). FSK and MFSK modes enjoy good immunity to noise and do not require a linear transmitter. MFSK modes were first developed in the 1950s and 1960s. The best known of these modes were Piccolo and Coquelet. An earlier experimental design by ZL1BPU and ZL2AFP, DominoF (with two sets of 8 interleaved tones) was in many ways most similar to Coquelet. The new DominoEX mode uses just one tone set, and has a more effective and efficient technique for tackling propagation effects.

DominoEX was specially designed for use on 80m at night, and to be easy for beginners to operate. The techniques used give independence from tuning and drift problems, and reception performance is so robust that error correction is generally not required. As a result the mode is quick to tune, very 'slick' (quick change from TX to RX) and has a high typing speed.

This ZL2AFP DominoEX version has optional (and automatic) Forward Error Correction (FEC). This mode is very robust, and FEC is not normally required. It can be helpful for ensuring that file transfers are accurate, especially under conditions of erratic lightning interference or severe multipath effects, but it does add delay and slows down data transfer.

In these documents, DominoEX means the operating mode in general terms, while ZL2AFP DominoEX specifically implies this ZL2AFP DominoEX program.

This program was written by Con Wassilieff ZL2AFP, using the PowerBASIC V8.02 Windows compiler. Con contributed the amazing synchronous waterfall, and patiently interpreted the design intentions into reality. The development took nearly two years, and many long evenings of code writing and testing.

The IFK+ modulation scheme, the Nibble Varicode, the Secondary Text idea, the soft decision FEC quality metric and various other sneaky algorithms were devised by Murray Greenman ZL1BPU. The convolutional coder uses a NASA standard algorithm, and the soft decision Viterbi decoder was provided by Con Wassilieff ZL2AFP, based on work by Phil Karn KA9Q, Peter Martinez G3PLX, Dr Knud Larsen and others. Much of the underlying MFSK technique, including the sync concept, the sliding DFT integrate-and-dump detector, the sliding matrix interleaver and the bit-wise MFSK16 varicode were provided by Nino Porcino IZ8BLY and Murray Greenman ZL1BPU, from work with MFSK16 in STREAM by Nino IZ8BLY. FEC coding for DominoEX was first released in MULTIPSK by Patrick Lindecker F6CTE.

Ionospheric research, and the design for NVIS applications was undertaken by Murray Greenman ZL1BPU, with the (perhaps unwitting) assistance of Peter Martinez G3PLX, Steve Olney VK2ZTO, Alberto di Bene I2PHD and Dr Gary Bold ZL1AN. Simulation was undertaken by ZL1BPU and ZL2AFP using the simulator PATHSIM provided by Moe Wheatley AE4JY. Most on-air testing was between ZL1BPU and ZL2AFP over a 500km 80m NVIS path, with additional tests over shorter and longer paths and on other frequencies thanks to ZL1AN, HB9BDM and many others.

DominoEX has a number of special advantages over other digital modes:

1. High tolerance of receiver drift and tuning offset.

   Unlike MFSK16, which requires a tuning accuracy of 4Hz, and a drift rate of less than 4Hz per minute, ZL2AFP DominoEX will handle an offset of up to 200Hz, and drift of 200Hz/minute, provided of course that the signal remains within the operating passband. In most cases you can tune the signal in with the receiver, not the software - making it as easy to tune as RTTY.

   NOTE: Not all programs with DominoEX have this feature - not all have correctly employed the IFK+ receiving technique - check and compare with ZL2AFP DominoEX!

2. Easy tuning.

   Not only is the tuning display clear and sharp, even when signals are weak, but you need only centre the signal within 100Hz or so. Other modes and other software require spot-on tuning, and make it difficult to tune weak MFSK signals.

3. Very fast receiver sync.

   Text is printed very soon after tuning is achieved (there is minimum latency, under one second, or 5 sec with FEC).

4. High tolerance of multi-path.

   DominoEX can handle about 60ms of multi-path error (by comparison RTTY copes with less than 5ms). Large multi-path errors are common with NVIS propagation (such as 80m at night), and where long and short paths exist at the same time.

5. Low data rates and narrow signals are practical.

   Low data rate options are viable without Doppler, drift and tuning problems. For example, DominoEX 8 performs well under the worst 80m conditions, is easy to tune, occupies a bandwidth of under 350Hz, and yet still goes at 50WPM - faster than PSK31! It is also more sensitive and much less error prone that PSK31.

6. High typing speed.

   With a Varicoded character set and no FEC (FEC = Forward Error Correction), a data rate of 70 WPM is achieved at the default symbol rate of only 10.76 baud. The character coding gives high efficiency at low data rates, and yet a full Extended ASCII character set (256 characters) is provided. The DominoEX mode is sufficiently robust that FEC is not usually needed. With FEC the data rate drops to 35WPM (same as PSK31 with no FEC!) For LF, try DominoEX 4 with FEC - still 12.5 WPM!

7. Excellent NVIS performance.

   DominoEX provides useful and easy communications on low HF bands impaired by multi-path (80/40/30m). RTTY would not give any readable copy under these conditions, and even PSK31 would be difficult. DominoEX also performs very well on higher bands since it has similar weak signal characteristics to MFSK16, yet is much easier tuning.

8. Secondary channel for automatic ID.

   The varicode allows a special set of characters is set aside for use as a 'secondary channel'. When the transmitter is idle (nothing in the keyboard buffer) it sends a fixed predefined message that is received in a special window. This is typically used as automatic station ID.

9. Synchronous Waterfall

   The ZL2AFP DominoEX program uses a Synchronous Waterfall, i.e. one which operates at the symbol rate, and is locked to it. This has four important advantages:

   • The signal is very sharp and clear, even when very weak.
   • Non-synchronous information (such as noise) disappears when a signal is tuned in.
   • The signal can be seen and tuned right down to the threshold of reception, well below the audible limit and at least 10dB better than any other similar program.
   • The effects of multi-path and Doppler are clearly visible as broadening of the dots on the waterfall.

   No other software compares with ZL2AFP DominoEX for sensitivity and clarity of waterfall tuning display.

As is sometimes the case with modes designed for a specific purpose, other applications are also made possible, almost by accident. DominoEX has been found to be the perfect mode for VHF DX - more sensitive than PSK31, easier to tune, and immune to drift. It also has high Doppler shift tolerance. Try DominoEX 22 for Meteor Scatter!

What - you really expected there'd be any? Well, let's be honest, there are a very few:

1. The mode is not as narrow as PSK31, but then it's still narrow enough for at least six DominoEX QSOs to fit in the bandwidth of a transceiver IF. It also works better than PSK31 under most circumstances, and gives far fewer errors.
2. There is some sensitivity to carrier interference in between the tones, although this is reduced with FEC on. Carrier interference is spread by the IFK+ technique.
3. Typing speed is fast, but still not really suitable for file transfer. There's also (as yet) no picture transmission mode.
4. Not enough software versions exist. So far there are two for Windows and two for LINUX, and only the Windows versions have FEC.
5. There are not enough operators using DominoEX!
6. Sensitivity under conditions of just noise is slightly less than some other modes (notably MFSK16).
7. It can be hard to tell the difference between DominoEX and MFSK16 at times. It's also only possible to determine which way up (which sideband) a signal is on, and whether FEC is in use, by trial and error (although ZL2AFP DominoEX has auto-FEC). These problems can be rectified by smarter software. See Signal Recognition.

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No performance is guaranteed, or promised, either expressed or implied, and no responsibility will be accepted by the authors if the program or documentation fails to live up to expectations, or causes your PC or radio to crash and burn. All care, but no responsibility.

This program and associated documentation are respectively © Copyright Con Wassilieff ZL2AFP and Murray Greenman ZL1BPU 2003-2005. Please do not copy, alter or publish without permission. All Rights are Reserved. No trade marking is claimed for the 'DOMINO' or 'DominoEX' names. Apparently the 'DOMINO' Trade Mark is variously owned by big blue and a well known fast food delivery company, which may say something about the flavour of computer products, or the performance of pizza!