A highly robust digital mode for HF, designed especially for NVIS propagation - useful for experts and beginners alike.
The new DominoEX replaces the older DominoF experimental mode. The two modes are not compatible.
An alpha release of DominoEX with FEC is now available! This is fully compatible with DominoEX and also with F6CTE's MultiPSK.
WINDOWS SOUND CARD PROGRAMMER WANTED - see note at bottom of page!
DominoEX is a computer-based radio mode intended for simplex chat-mode operation on the lower HF bands, although the performance is excellent from LF to VHF. You can use any SSB transmitter, even an old "steam radio" type. DominoEX has been designed to get around several problems which exist with other digital modes, such as difficult tuning, slow response, and poor performance on the 80 - 30m bands.
- DominoEX is so robust that Forward Error Correction (FEC) is not usually required for perfect print.
- The new mode is so 'slick' that it would be useful for contesting. It is great for nets - it's as slick as RTTY, faster, and far better!
DominoEX is a digital mode with MFSK (Multi-Frequency Shift Keying), used to send data (for example, hand-typed text) by radio. MFSK sends data using many different tones, sent one at a time. Each tone element ('symbol') can carry several bits of data, unlike most other modes, where each element represents only one bit. Thus the symbol rate is much lower for the same data rate when MFSK is used. This is beneficial, since it leads to high sensitivity with good data rate and modest bandwidth. Even more important, low symbol rates are less effected by multi-path reception timing effects.
Thus MFSK is ideal for HF operation, since it has good noise rejection and good immunity to most propagation distortion effects which adversely affect reception of other modes. MFSK is already used on HF by modes such as MFSK16, ALE, THROB and Olivia. DominoEX is a narrow mode (more like MFSK16 or RTTY).
The narrow-band MFSK technique has a few limitations. The main disadvantage is that radio transceivers with high stability and tuning accuracy are generally required, since very narrow frequency differences are used. MFSK is also prone to interference from data arriving from different ionospheric paths (although less so than other modes), and prone to interference from fixed carriers within the data passband. With Forward Error Correction (FEC) deployed to reduce errors, these modes can become slow and clumsy to operate, or consume excessive bandwidth. With DominoEX, we have taken a different approach, concentrating on perfecting the design for best NVIS (Near Vertical Incidence Signal) reception. All the inherent MFSK problems are also avoided or much reduced.
DominoEX uses a series of new techniques to counter the general limitations of MFSK. To avoid tuning problems, IFK (Incremental Frequency Keying) is used, where the data is represented not by the frequency of each tone, but by the frequency difference between one tone and the next. An additional technique, called Offset Incremental Keying is used to counter inter-symbol interference caused by multi-path reception. This gives the mode a great improvement in robustness.
DominoEX offers:
- simple QSO mode with the usual features
- incredible tuning tolerance - up to 200Hz offset
- incredible drift tolerance - up to 200Hz/minute!
- typing speed 50 to 100 WPM, low bandwidth
- no need for a highly linear transmitter
- designed specifically for 80/40/30m
- secondary (ID) channel for full-time transmission identification
- varicoded data for higher throughput - up to 140WPM!
- high multi-path tolerance for NVIS conditions
- lower error rate - no FEC required!
- full extended ASCII character set
- FEC option offered for secure copy under the poorest conditions
- Combination of IFK+ and FEC substantially eliminates carrier interferenceDominoEX will handle TX/RX offsets and mistuning of up to 200Hz with ease. It also has better (by design) multi-path performance than other modes, and this means low-error copy without requiring FEC, which in turn means faster typing and quicker response. FEC can be switched in (where offered - depends on the program) where needed, and gives 100% copy under marginal conditions plus reduction of carrier interference effects. Automatic FEC detection and switching is also offered in the ZL2AFP DominoEXFEC program.
No one mode can be perfect for all conditions. When propagation is stable (line of sight, VHF tropo, or single hop on higher bands) high speeds are possible, offering enhanced performance with good tuning tolerance and reasonable robustness (rejection of interference). When conditions deteriorate, multi-path propagation can cause timing errors, and a slower mode is indicated. The slower modes also have better sensitivity. This approach can be likened to 'changing down' in a manual car (stick-shift automobile) when the going becomes tough.On the lower bands there is considerable noise, and during the early evening quite severe multi-path propagation, requiring slower speeds. The tone spacing of MFSK modes must be related directly to the baud rate, and the narrowest practical spacing is numerically the same as the baud rate. Because the slower speeds imply using closer tones, which could lead to Doppler problems (well known to PSK31 users), these slower modes use double tone spacing to avoid the problem.
Six speeds are currently offered. The faster modes are best used on the higher bands and when conditions are good (modes shown with pink background in the table). There are also three s l o w modes designed for poor conditions and the lower bands. These modes are more sensitive, and have double tone spacing, which improves performance further by reducing the effects of drift and Doppler. Choose the one you need for the prevailing conditions. On higher bands, start with 11 baud (the default speed) and change up if conditions are good, and down if they deteriorate. 8 baud up to 16 baud are excellent for NVIS propagation on 80m. Use 8 baud when the band is especially noisy, or simply switch in the FEC option.
MODE BAUD BW TONES SPEED FEC TONE SPACING DominoEX 4 3.90625 173Hz 18 ~25 WPM ~12 WPM Baud rate x2 DominoEX 5 5.3833 244Hz 18 ~31 WPM ~16 WPM Baud rate x2 DominoEX 8 7.8125 346Hz 18 ~50 WPM ~25 WPM Baud rate x2 * DominoEX 11 10.766 262Hz 18 ~70 WPM ~35 WPM Baud rate x1 DominoEX 16 15.625 355Hz 18 ~100 WPM ~50 WPM Baud rate x1 DominoEX 22 21.533 524Hz 18 ~140 WPM ~70 WPM Baud rate x1 Table of DominoEX modes. * Default mode (with FEC off)
The speeds quoted for DominoEX are approximate for typical text in English. For speed measured in Characters per Second (CPS), divide the above values by 10. Speed varies slightly with content. Speeds and parameters have been chosen following extensive on-air and simulator testing. The lowest speeds are suggested for QRP beacons - DominoEX has a full-time (secondary text) beacon built-in!
DominoEX works by sending short transmissions of 18 different tones (called symbols), one at a time, each carrying four bits of data. So DominoEX is an MFSK mode, meaning it is naturally sensitive, resistant to interference and ionospheric effects. Several new techniques are used.These features make the mode easy to use, easy to tune, convenient, and ideal for beginners.
- DominoEX uses an Offset Incremental Frequency Keying incremental coding algorithm called 'IFK+', developed by Murray Greenman ZL1BPU, which avoids repeated tones (inter-symbol interference strategy) and gives strong sync. It is so robust that FEC is not needed.
- IFK+ means that data is carried in frequency differences rather than absolute frequency, so also gives complete independence from tuning errors and drift.
- DominoEX also has automatic nibble sync, nibble varicoding to give a large character set, and secondary channel data transmitted when the keyboard is idle. These features are designed into the character set, and add no overhead to the sending speed.
- With FEC activated, DominoEX uses the spreading effect of IFK+ to mitigate the effects of carrier interference.
- fast typingDominoEX is based on 'nibbles' of information (four data bit entities), and since exactly one nibble can be transmitted on each tone element (which we call a 'symbol'), the mode can be very efficient. When transmitting text, the specially designed character set is defined in nibbles, marked with an identifier bit to ensure automatic nibble sync. Each character transmitted consists of one, two or three nibbles (that is, one, two or three sequential tones), depending on whether the character is often or rarely used. The frequency of each tone (symbol) transmitted represents the mathematical difference between one nibble and the next (actually the increment from the last tone number to the next tone number represents the value of the next nibble).
- automatic ID
- very quick to tune
- needs no error correction
- retune without losing data
- faster sync than other modes
- designed for slick QSO exchanges
- full extended ASCII character set
- with FEC, perfect copy down into the noise
- European accented characters and simple graphics
The identifier bit in each nibble (which provides character synchronism) is automatically discovered because of the bit weighting, and used to decide the nibbles to be used to decode each character, or the order in which they should be arranged for bit-wise use. DominoEX cleverly uses one-, two- or three-nibble character sequences, almost doubling the text speed (say compared with ASCII), because more frequently used characters use fewer nibbles. The varicode allows a very large character set (584 characters!) to be accommodated. Because of the way the character set is defined, no extra sync bits are required - they are built into the character set.
With FEC activated, the transmission changes to a bit-based system similar to MFSK16, and the same varicode is used (except for the addition of the secondary text). A bit-based system allows the use of robust convolutional coding and decoding error correction techniques, although the typing speed is halved. IFK+ continues to provide the same advantages.
The receiver measures the frequency difference between successive symbols and calculates the nibble value to be decoded into characters or groups of bits. Because frequency measurement is made with high resolution (¼ of the tone spacing), differential tuning errors (such as drift and frequency offset) can be rounded out. Because measurements are made synchronously, i.e. exactly over the whole duration of each symbol, and on nothing else, there is high sensitivity and very good rejection of multi-path distortion and other inter-symbol interference.The Offset Incremental Frequency Keying IFK+ algorithm also ensures that no symbol is followed by another on the same or an adjacent frequency, and so no overlap can occur between tones arriving via different paths, to degrade reception. A fixed offset or increment is added to each symbol, causing the tones to rotate and avoid previously used tones. This considerably enhances the already good multi-path performance. Since symbol sync is recovered by studying the response to the tones in the receiver (no sync is transmitted), the sync is also enhanced because there can never be a missed sync edge caused by two sequential tones the same.
The algorithm also randomises the effects of carrier interference. Although errors will still occur, copy can often be maintained rather than stopping dead, as happens in MFSK16 under similar circumstances. When FEC is turned on, the errors caused by carrier interference are spread by the IFK decoder and again by the FEC de-interleaver, and may be completely corrected. The results are impressive, and much improved over MFSK16 and other MFSK modes, which cannot spread these 'stuck bit' errors.
You can also tune the signal while receiving, to push an interfering carrier (but not one between the tones) out of the active receive region.
MFSK was first developed in the 1950s, and most subsequent development went into wider band high speed systems. The first real narrow-band improvement was the use of a binary convolution FEC system (as in MFSK16, developed in 1999). Some theoretical work had been done on tone field management for high speed applications, but until the work undertaken by the author ZL1BPU and Con ZL2AFP in 2004, very little had been done to develop simple, robust MFSK techniques with high tuning tolerance and ISI enhancement strategies for narrow-band use.Other developers have concentrated on getting around the problems of conventional MFSK by using wider, faster transmissions with strong FEC (for example ALE and Olivia) The FEC is used to mask the underlying problems in the modem, but at the expense of wider bandwidth, unacceptable latency, or both. Virtually nothing was known about the performance of IFK modes on HF until the experimental work using DominoF was carried out in 2004. None of the existing modes, or even more recent modes such as Olivia, were optimized for noisy low HF bands where NVIS conditions predominate.
DominoEX has been designed with these parameters in mind and provides, for the first time, a viable MFSK mode for beginners on low HF bands, and a viable replacement for RTTY. Its characteristics also make it a good mode for the HF DX bands and for VHF.
If you:
- find digi-modes difficult to usethen you should be using DominoEX!
- have trouble tuning in the signals
- can't see the weak signals to tune them in
- are looking for a better mode for contesting
- can type faster than your favourite digi-mode can send
- tire of complaints that your rig drifts, or is off frequency
- are looking for a digital mode for Emergency Communications
- have difficulty copying signals reliably under NVIS conditions
- wish to have error free copy of signals right down into the noise
With no error correction, copy at -10dB S/N in 3kHz bandwidth (a signal you can barely hear) is nearly as good as MFSK16, (which is error corrected), and better than PSK31 and MT63. With FEC on, at this signal level you will copy 100% for hours at a time. Simulations have shown that it is also significantly more robust under poor propagation conditions. Unlike MFSK16 and many other modes, it is easy to tune. The mode has special properties, suited to the lower bands especially, (outlined above). There may well be better ways to do what DominoEX does, especially with regard to receiver design, and if you are a software developer, we would like your help to find them.
An experimental "Sentence Mode" of operation has demonstrated that an ARQ mode based on this technology would be viable. The sync will lock in just four or five symbols, so operation of this mode is sufficiently 'slick', that with VOX or PTT connected you can type overs as individual sentences or just a few words (rather like using an internet chat facility, or chatting on packet radio). Great for nets - how many other modes can do that?
The ZL2AFP DominoEX program needs Windows™ (95, 98, 2000 or XP), with a 120MHz Pentium™ processor or better, under 1MB disc space, 64MB of RAM and Soundblaster™ type full-duplex sound card, 640 x 480 VGA display or better. (For 22 baud and FEC a >300MHz computer is best). The program will even operate from a floppy disc, and does not make registry changes. The installation procedure consists only of copying only one executable file and making a shortcut to it.There is also now a LINUX version, which should work with most Knoppix, Debian, Ubuntu and Hamshack Hack distros.
You will also need the usual sound card radio interface and cables used by many other modes. VOX or PTT operation is possible.
- use any HF SSB transceiver
- need not be a modern one
- old radios such as the FT101 will do nicely!Download the free software archives (see below). Unzip to install the software. The Help information is available online and can be downloaded to work with the ZL2AFP program.
The signal sounds rather like MFSK16, a musical jumble of notes, but listening carefully, can be differentiated by ear. Several modes have a similar sound, but can be identified with care:- DominoF had an unusual "falling" sound to the tones, most obvious during idle, and sounded slower than MFSK16DominoEX has no single idle tone, in fact idle cannot be recognised at all. It is hard to tell if DominoEX is received inverted, but the main data and secondary text won't print. The correct speed is always identifiable because the waterfall display will look sharp if correct, and blurred if incorrect. Use the Confidence Meter (in the FEC version) to determine whether FEC is on or off.
- DominoEX has a very jumbled sound to the tones, no obvious idle, and usually sounds slower than MFSK16
- MFSK16 has jumbled tones, but a distinctive low tuning tone to start, and settles musically to a low tone during idle
- Olivia has very jumbled tones, much faster and wider, and a distinctive 'nee-naw-nee-naw' sound at the start of transmission
- ALE is much faster and wider, and sounds like a turkey gobbling - it has only 8 tonesThe default speed for DominoEX (11 baud) sounds slower than MFSK16, and is narrower (around 260Hz).
Note that there are only six speed options offered, all easily discernable by ear, and no other adjustable parameters. FEC defaults to OFF, and in ZL2AFP DominoEX turns on automatically as needed.. The designers are totally opposed to releasing software with so many options (many of them questionable) that simply confuse users and make a common format for QSOs impossible. The research work should be carried out by the developers, before release, and not left to the users!
The DominoEX software might look simple, but is really great stuff:- superb "point and drag" waterfall display for easy tuning
- waterfall is clear to see even with weak signals
- waterfall indicates correct speed setting
- fast and slick keyboard control
- automatic FEC at the receiver
- does not change the Registry
- simple macros for easy QSOs
- intuitive and easy to use
- easy on the eye
- free softwareThe software has a familiar look and feel. It is modelled on the famous MFSK16 program STREAM by Nino IZ8BLY. ZL2AFP DominoEX has an extra 'Secondary Channel' window at the top, which displays the callsign or other message from the transmitting station in 'Times Square' (scrolling) fashion. The waterfall display is clearer and sharper than all other MFSK programs! The example below was recorded using a signal with no FEC at -10dB S/N in 3kHz bandwidth - barely audible by ear. Enlarge the picture and note the quality of the text (no errors in over 300 characters) and the clarity of the tuning display:
Screen shot - ZL2AFP DominoEX
(Click on image for larger view)How many other modes - with or without FEC - will deliver 77 WPM with 100% copy at -10dB S/N, while using only 260Hz bandwidth?
And are they as easy to tune? Easy to use?
DominoEX is at present available in three different programs - the original DominoEX by Con ZL2AFP, MultiPSK by Patrick F6CTE, and gMFSK for LINUX, adapted by Hamish VK3SB. The FEC option is available in MultiPSK and now in the DominoEXFEC alpha from ZL2AFP. The ZL2AFP program has been tested on Windows™ 95, 98, 2000 and XP, desktops and laptops. Negotiations with other developers are under way, and as other developers and platforms come on board, their details will be added here. Check here frequently for updates.
Would you like to see DominoEX in MIXW?
- We need an experienced Windows sound card programmer capable of working with Microsoft MFC and the free Microsoft C compiler in order to build a definitive DominoEX DLL for MIXW.
- We can offer all documentation and source code for a fully working program (ZL2AFP's version), as well as source and compiled DLL for a preliminary (limited but semi-working) DLL written by Denis UU9JDR of the MIXW team. You can expect support from ZL1BPU, ZL2AFP and UU9JDR. The FEC details are available from F6CTE - the FEC coding technique is identical to MFSK16.
- If you believe you have the skills and are prepared to build an open source freely available DLL compatible with MIXW, please contact ZL1BPU.
Versions for MULTIPSK and LINUX now available! Please wait patiently for support from IZ8BLY STREAM and MIXW...
Local Site (ZL):
ZL2AFP DominoEX release version 1.0, 4 to 22 baud (19 Dec 2005, 76kB)
ZL2AFP DominoEX beta version 1.0 with Sentence Mode, 4 to 22 baud (17 Nov 2005, 76kB)
ZL2AFP DominoEX Help - V1.0. (for above version, extract archive to folder containing above executable)
ZL2AFP DominoEXFEC alpha version 2.0c, 4 to 22 baud with FEC (30 Nov 2006, includes HELP, 252kB)
ZL2AFP DominoEXFEC beta version 2.0d, 4 to 22 baud with FEC (4 Dec 2006, includes HELP, 252kB)
ZL1BPU Mirror Site (EU)
F6CTE MULTIPSK with DominoEX and FEC!
VK3SB gMFSK LINUX DominoEX version!Mirror Site (USA):
ZL2AFP DominoEX release version 1.0, 4 to 22 baud (19 Dec 2005, 76kB)
ZL2AFP DominoEX beta version 1.0, 4 to 22 baud (17 Nov 2005, 76kB)
ZL2AFP DominoEXFEC alpha version 2.0c, 4 to 22 baud with FEC (30 Nov 2006, includes HELP, 252kB)
ZL2AFP DominoEXFEC beta version 2.0d, 4 to 22 baud with FEC (4 Dec 2006, includes HELP, 252kB)
Online Help file
Technical details
Frequently asked questionsSource Code registration (email)
Old versions ZL2AFP DominoF and ZL2AFP DominoG are still available for comparison purposes, but their use is now discouraged. The DominoF Help File is also available (choose File/Save Page As... and save in same folder as DominoF). Source code is public domain and delivered to genuine developers by email. A 'Developers' Pack' containing specifications and technical details, example reference executables and source code is also available. Developer registration ensures that updates can be sent. Serious enquiries only please. Developers interested in adding DominoEX to their software suite should contact Con Wassilieff ZL2AFP.
There is also a 'DominoEX Beginners' Powerpoint™ presentation and associated commentary available on application. We would also like to hear about technical improvements, other related techniques and ideas for robust tuning tolerant MFSK modes including ARQ modes. Report your experiences and experiments on the MFSK Reflector.
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 - you're on your own!
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.
