ZL2AFP DominoEX HELP

Description

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 the experimental DominoF and DominoG programs, and is not compatible with them.

This mode 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. 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 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 DominoF (with two sets of 8 interleaved tones) was in many ways most similar to Coquelet, which used two tone sets, one with 8 tones, the other with four, used wide spacing, and directly coded the ITA2 character set into sequential tone pairs. The new DominoEX mode uses just one tone set, but has a more effective and efficient technique for tackling propagation problems, and many other improvements.

The techniques used give independence from tuning and drift problems, and reception performance is so robust that error correction is not required. As a result the mode is quick to tune, very 'slick' (quick change from TX to RX) and has a high text speed, typically about 7x the baud rate.

Incremental Keying

DominoEX employs a method of transmitting data by encoding not the actual data to be transmitted, but the difference between the current data and the last transmitted piece of data. This technique was invented by Steve Olney VK2ZTO, and used first for extremely narrow band transmissions (where drift problems can be challenging). It was first successfully employed on LF by Alberto I2PHD in the JASON program, and for the first time at typing speed on HF in the earlier DominoF. This technique of difference encoding is called IFK (Incremental Frequency Keying). The new DominoEX mode takes this technique to a new level with an improved algorithm we call IFK+. IFK+ is used to give easy tuning, freedom from drift problems, and an efficient means of reducing multi-path interference and improve robustness.

Techniques

New techniques have been developed, and old techniques revived, by Con ZL2AFP and Murray ZL1BPU, in order to carefully optimize the signal spectrum and the way data is transmitted. The mode was developed specifically for low HF bands where multi-path reception is a problem. The software was designed for beginners with limited skills and perhaps equipment with limited performance, and to operate easily and quickly. It is this combination of techniques which give DominoEX its unique character:

• Incremental Frequency Keying to provide independence of tuning.
• Receiver impulse response analysis is used to provide very fast symbol synchronism. (Sync is NOT transmitted!)
• Latency (time taken for data to leave one end of the link and arrive at the other) is under 1 sec including the time taken to operate the transmitter VOX, the radio link propagation time, receiver decoding and sync lockup time!
• A tone set management algorithm prevents repeated tones in order to provide very good ISI performance (ISI = Inter-Symbol Interference). The tone set is managed so that ionospheric modulation products cannot easily spill from one possible tone position to another, or from one symbol to the next. This is done by always adding two to the tone number, even if the data to be sent is a repeat of the one before. This is the essence of the IFK+ algorithm.
• The design is character based, not a binary system or bit-based system. Most characters consist of two symbols. This technique was first used in Coquelet, and according to the Coquelet developers, two symbols per character offers the best signal to noise performance and error rate for an MFSK coded system.
• A unique character-based Varicode alphabet coding scheme is used. Each group of one, two or three tones mean a specific character. The most used characters consist of just one tone, and the rarely used ones three tones. The improvement in text speed over a fixed alphabet is about 1.4:1, and by using the varicode the character set can be unlimited in size. Character sync is efficient because it is designed directly into the character set.
• A low data rate is used (typically 10.76 baud or 10.76 symbols per second). The low data rate is important to defeat the timing effects of multi-path reception.
• Three similar modes with different speeds are offered so performance can be matched to conditions.

Advantages

DominoEX gains a number of special advantages through using these techniques:

1. IFK+ used in DominEX provides high tolerance of receiver drift and tuning offset. (The DominoEX software will actually copy signals while the receiver is being tuned!) Unlike MFSK16, which requires a tuning accuracy of 4Hz, and a drift rate of less than 4Hz per minute, DominoEX will handle an offset of much more than 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.
2. Receiver lockup and sync are very fast. Text is printed very soon after tuning is achieved (there is minimum latency, under one second).
3. Because of the special IFK+ algorithm, and the low data rate, 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 (up to 60ms).
4. Very low data rates and very narrow signals can be practical without drift and tuning problems. (DominoEX 8 performs flawlessly under the worst conditions, is easy to tune, occupies a bandwidth of only 178Hz, and yet still goes at 50WPM - faster than PSK31! It is also more sensitive and much less error prone that PSK31.
5. With a Varicoded character set and no FEC (FEC = Forward Error Correction), a data rate of 70 WPM is achieved at a symbol rate of only 10.76 baud. The DominoEX mode is sufficiently robust that FEC is not really needed. (An FEC option is now available in versions - it is very effective, but halves the typing speed.)
6. 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.
7. The character coding gives high efficiency at low data rates, and yet a full Extended ASCII character set (256 characters) is provided.
8. Text, raw and error corrected data, files and graphics could be transmitted in future versions because the system design is modular and based on four-bit data entities.
9. Varicoding allows characters outside the normal character set to be defined for other purposes ('super-alpha' characters). These can be used for control purposes, since they are non printing. The many unused 'super-alpha' combinations are also non-printing, and act as a simple means of suppressing characters received in error.
10. A sub-set of 'super-alpha' 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.

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.

Signal Recognition

It is very important for digital modes to be easily recognised and identified. Thus the onus is on the designer to provide something unique for each new mode. Of course MFSK modes can be easily separated from other modes by their musical sound.

• MFSK16, the most popular MFSK mode, has a single idle tone which appears at start of transmission, and again periodically while the transmitter is idle.
• Throb has a soft edged sound, two tones which frequently beat with each other, and a very slow data rate.
• Olivia sounds fast, very wide, and sounds very jumbled. It has a unique 'nee-naw-nee-naw' sound at the start of transmission.
• DominoF can be identified by the insistent "falling" sound to the tones when idle or between words.
• DominoEX can be identified by complete lack of any apparent idle sequence, and no starting tone.

The several different DominoEX speeds can be identified by ear (listening to the cadence) or on the waterfall, by the clarity of dots. If the waterfall dots are indistinct, the selected speed is probably incorrect.

On the waterfall display, while the transmission is idle, the DominoF signal (see left picture above) looks like a series of downward pointing stair-steps, in a very regular pattern. DominoEX has no such pattern (see right picture above). It tends to look jumbled all the time. During idle, there is a slight increase in the density of higher tones.

The speed can also be identified by the apparent bandwidth on the waterfall - for example about 200Hz for DominoEX 11, and about 300Hz for DominoEX 16. If the speed is set incorrectly, the waterfall will be blurry, with dots of uneven brightness, and the problem obvious. Tuning is easy. Just keep all the signal between the two yellow lines, one in the middle and one at the bottom of the waterfall display, either by tuning the receiver, dragging the tuning scale to the left of the waterfall display, or dragging the display itself.

Installation

Simply unzip the archive into an appropriate folder on your hard drive. Only one executable (.EXE) file is required. Create a link to it, by right-clicking on the filename in Explorer (see picture on right). You can then drag this shortcut to the Desktop or Task Bar. A setup file will be created when you first start the program. Any other files in the archive will be associated with this help system, and if needed, should all be unzipped into the same folder as the executable.

The program should work on any PC with Windows™ 95 or later, provided it has a Sound Blaster™ compatable sound card. A computer speed of 120MHz and 32MB of memory should suffice, although the computer will be much more responsive on faster computers. 16 baud and 22 baud speeds may not work correctly on anything slower than a 300MHz Pentium. You will also require suitable cables or an interface for connection between the sound card and the HF transceiver.

Start the program by double-clicking the executable program filename in Explorer, or using the shortcut you have created. A single window is displayed, containing all you will need for enjoyable QSOs. The first thing to do is to set the user's callsign by clicking on Options on the menu bar, and dragging the mouse down to Callsign. This allows the automatic 'macros' to generate the required information. You can also set the 'Secondary Channel' text here.

The size of the application window is adjustable. The default size is 640 x 480, but it can be dragged wider and taller by left-clicking on the right or left edge, or on the bottom right corner, and dragging with the mouse button down. The tuning display graphics are of fixed size, so stay the same when the screen is enlarged. The window can also be made to take up the full screen using the Maximize button on the program banner (top right).

Setting up the sound card is no different from other modes. Set the receive signal level by adjustment of 'Line In' on the Recording Control Applet, which can be called up from the Menu Soundcard/Input item. Make sure that the 'Line In' tick box on the applet has a tick showing. Set the transmitter level by adjusting the Wave slider on the Volume Control Applet, which can be called up from the Menu Soundcard/Output item.

It does not matter too much if the transmitter operates non-linearly, but it is best to keep drive to the minimum necessary, in order to reduce the risk of hum and transmitter overload. Remember also that if the sound card output is too high, or the level into the rig is too high, clipping can result. Assymetrical clipping causes second harmonics to be generated, and these will still be within the transmitter passband, and will appear on air. A good guide is to keep the sound card level down to about 1/4 and adjust the input level to the rig just below where there an ALC indication. Your transmitter will be happier if you keep the power down on long overs. The mode is very sensitive and 1W output power will give you an impressive operating range.

Guided Tour

The program consists of just one main window, from which all settings and features are accessed. There are several main areas to consider. These are:

• Menu
• Secondary Text Bar
• Transmit Window and Receive Window
• Tuning Displays
• Macro Buttons and Control Buttons
• Status Line

Bear in mind that your version of the software may have slightly different menu options, and they may be differently arranged to those shown. It is very difficult to keep the help file as current as the software releases. This description applies to version 1.0 Build 13.11.05.

Menu

At the top of the main window underneath the "banner" is a line of text reading "File   Mode   Options   Tools   Soundcard   Help". If you click on any of these, various options are available via drop-down menus. You will note that some of these items have the first letter underlined. This indicates that the menu can also be brought up using the ALT key, so the menu can be navigated with cursor keys.

File / Send file

Brings up a file selection dialog to allow a text file to be transmitted (should only be used for text files). The file is copied into the transmit buffer, but not into the keyboard buffer. It is best to use the yellow Stop file/Clear TX screen Tool Bar button once the file has been sent, to ensure that the TX buffer is cleared for further use for manually sent text. Without clearing the buffer, unpredicatable things may happen, such as typed text being lost and not transmitted. There is no provision for data files or images to be transmitted, and no mechanism for receiving and saving files (yet!). The transmitter is not automatically started when you select a file for transmission.

File / Save RX screen to file

Saves the current receive screen to a file in the same folder as the program. The file name is automatically assigned, for example 'IFK+save074923.doc'.

File / Exit

Closes the program immediately, even when in transmit, and releases the sound card.

Mode

Allows each of the six operating modes to be selected. The current mode is indicated with a tick (check) mark. You can't change speed while transmitting, as the program drops back to receive. The range is from 4 baud to 22 baud:

	MODE	BAUD	BW	TONES	SPEED	TONE SPACING
	DominoEX 4	3.90625	173Hz	18	~25 WPM	Spaced baud rate x2
	DominoEX 5	5.3833	244Hz	18	~50 WPM	Spaced baud rate x2
	DominoEX 8	7.8125	346Hz	18	~50 WPM	Spaced baud rate x2
*	DominoEX 11	11.025	262Hz	18	~70 WPM	Spaced baud rate x1
	DominoEX 16	15.625	355Hz	18	~100 WPM	Spaced baud rate x1
	DominoEX 22	21.533	524Hz	18	~140 WPM	Spaced baud rate x1

* The default mode (marked pink in table) is 11 baud spaced baud rate x1.

Options / Callsign

Sets the operator's callsign for use in macros. A simple dialog box allows the callsign to be entered.

Options / Save RX to file?

Permits automatic periodic capture of RX screen to file. Marked with a tick (check) mark when active. See File / Save RX screen to file.

Options / Secondary channel text font

Sets the font and size used for the received secondary channel text message window. 10 to 12 point fonts are suitable. Color is always black.

Options / Secondary channel text

Sets the secondary channel text message. Should contain at least user's callsign, but can also contain user's name, location and weather etc. A simple dialog box allows the text to be entered.

Options / Received text character set

Sets the secondary channel received text character set. Can be 'All 256 ASCII characters' or 'Restricted to 64 ASCII'. Restricting the character set can make Secondary Text easier to read under very poor conditions. The transmitted character set is not affected, but can be restricted through choice of message characters (numbers and upper case).

Options / Secondary text echo?

Sets whether the outgoing Secondary Text is echoed in the transmitting stations Secondary Text window. Marked with a tick (check) mark when active. The text will be black.

Options / PTT settings

A small window comes up when you click on this, allowing the serial port used for PTT control to be selected. Any port from COM1 to COM9 can be selected, and "none" is a valid option. PTT operates by raising DTR positive for transmit. Note - the little dialog box tends to hide under the main window!

Options / Symbol sync filter

Selects options for symbol sync filter time constant. 'A little sync average' is the default in normal (keyboard) mode, and 'No sync average' is the default in Sentence mode. 'A lot of sync average' can be tried when conditions are very difficult. The symbol sync filter has three time constants; 0, 1 and 8 symbol periods, corresponding to 'No sync', 'A little' and 'A lot' respectively. A longer filter time constant can reduce the effect of noise. There is a slider under the waterfall that can also set this filter to the same values.

Options / Keyboard mode

In 'sentence' mode, transmission starts when you press ENTER, and stops when the point in the transmit buffer where you pressed ENTER is reached. This is used to send single short comments, typically in net operation. In 'Keyboard' mode, transmission does not start until you press Transmit or ALT T, and stops when you press Receive or ALT R, or <EOT> is detected in the buffer. In this mode ENTER is transmitted the same as any other character. This is the default option. The chosen option is indicated with a tick (check) mark when active.

Tools / Squelch trigger level

Sets the signal to noise ratio at which text will print. The default value is 5, and increasing the value reduces the sensitivity.

Tools / Bandwidth capture range

Sets the width of the active receiver bandwidth. This in effect moves the upper yellow line on the tuning display as well as changing the capture range. The default value is 122, and decreasing the number decreases the bandwidth (lowers the yellow line). Wider bandwidth increases the risk of poor copy due to carrier and noise interference, while narrower bandwidth requires more care with tuning and lower drift tolerance. Setting much less than 120 will result in zero copy. Best not to fool with this one!

Tools / Receive input attenuation

Sets a coarse gain on receiver sensitivity. The default value is 1, and should suit everyone. Fine adjustment is done using the Recording Control Applet (see below).

Tools / AGC for waterfall display

Sets the AGC threshold, i.e. where AGC starts acting. The AGC is detected from the waterfall FFT, so acts faster than the symbol rate.

Tools / Delete current file being sent

Does just that! Otherwise you can get into a heap of trouble when you try to send a file that turns out to be bigger than you expect. The file isn't lost - it is just removed from the transmitter queue.

Help / Help

Calls up this Help file (specifically "DominoEX.htm" in same folder as program).

Help / About

Calls up a small box giving version information, credits and copyright details.

Secondary Text Bar

A small window across the top of the program below the menu is used to display "Secondary Text". This data is sent whenever the user's typing is not keeping up with the native speed of the mode, and is used to send a fixed ID or informative message. Both the transmitting station's message (during transmit) and the message of the station being received are shown here, scrolling along like an advertising display in a single line. This handy feature is unique to DominoEX. A button labelled '2nd' to the left of this window allows you to access a dialog to change the Secondary Text message. You can change the message any time - including while on transmit. This message should always include your callsign, but can include anything else, up to 256 characters. Shorter messages are better. Messages over about 60 characters will overflow the receive display, and will be scrolled through as new text arrives.

The Secondary Text provides an instant Beacon Mode. Set the message you want, and start the transmitter! It is also a handy feature for net control instructions and can be useful for advertising skeds, operating location and equipment - you name it!

Receive Window

The Receive Window is the large window (white background) immediately below the Secondary Text Bar. Anything received appears here, including junk between stations if the squelch is set low. Whatever is transmitted also appears here too, but only as the characters are actually transmitted. When the last transmitted text appears here, you can return to receive.

Normally the text appears sequentially line after line, with old text scrolling off the top of the display. However, by clicking in the window, it is possible to change the "insertion point" so the text will (in a most confusing manner) appear before text already received. Normally this is no issue, but if you click in the Receive Window in order to cut and paste text, remember to return the insertion point below the last received text. text can be copied from this window by highlighting with the mouse and pressing CTRL+C.

Transmit Window

The Transmit Window is the smaller text entry box (white window) below the Receive Window. Anything you type here will be sent to the transmitter once transmission is started. The same comment about the insertion point applies - it is possible to edit text by moving the insertion point (clicking in the window) and then continuing later to type at the end of the text by again moving the insertion point. Some points to note:

1. If you click away from the TX window, anything you type will either go off into space (i.e. nowhere useful) or into the Receive Window, which isn't especially helpful. Make sure to return "focus" to the TX Window after clicking in the RX Window, by left-clicking in the Transmit Window after any text already there.
2. You can "type ahead" by typing in the TX Window while you are receiving. When the transmission is subsequently started, the text already in the buffer will be sent first. It is not advisable to change speed with text in the buffer.
3. You can copy and paste text from the Receive Window to the Transmit Window, and even from one point in the TX Window to another point in the same window, but take note of the comments above about the insertion point. You can also copy and paste from any other application that supports it (e.g. a text document). Use CTRL+V to paste into the Transmit Window.

   Macro text appears in the Transmit Window after macro keys are pressed. File text is sent without appearing in the Transmit Window.

Tuning Displays

Three tuning displays are provided. The largest and most obvious is the Waterfall Display, the upper-most of the group on the right of the Receive Window. This indicates the signal tuning, and the quality of the received signal. Because the DominoEX Waterfall is synchronous with the signal, it will give a very sharp and clear display if the signal is of the correct type, and will be slightly blurred if it is not. Each little white dot (domino pip?) represents a burst of tone, or symbol. The scale on the left is frequency, in Hz, and changes when the mode is changed. The bottom of the scale (by default 1000Hz) is set by sliding the waterfall with the mouse.

The waterfall clarity is superb - you can always see the signal, even if it is very weak. The DominoEX example to the right was recorded with the signal 10dB below the noise in a 3kHz bandwidth, and the signal can be tuned by eye down to -15dB! Most other digital mode software is very difficult to tune with the signal below the noise, because you can't tell signal from noise.

The waterfall image moves left to right with time, and can be dragged up and down to tune the signal. Two yellow lines are visible on the display - one in the centre of the waterfall, the other right at the bottom of the waterfall. If all the signal falls between these two yellow lines (which are preset to indicate the receiving range), then the signal will be decoded correctly. It does not matter where in this window the signal falls, or if it drifts (provided all of the signal stays within the yellow lines). This gives you up to 200Hz of tuning latitude.

In the example to the right, you can see the signal as a series of little white stripes over the range 1030 to 1230Hz. The signal is only roughly centred between the yellow lines, and is about 200Hz wide. Adjustment of Waterfall tuning is described under Receiving (below). When there are significant problems caused by multi-path reception, the distinct little white stripes will show broadening or transient effects. When this becomes quite marked, copy will suffer, and a slower mode should be used. As the signal gets weaker, the noise background becomes more obvious, but you will be able to easily tune any signal that could be copied.

Below the Waterfall Display are two small Sync Displays. Their main purpose is to illustrate received timing variations. They can be useful when considering using different speeds. On the left, a cumulative indication of symbol sync versus time is shown. This is useful as an indication of multi-path reception, and the sync can often be seen to change abruptly when there is a fade. This display moves from left to right, and illustrates the tips of the sync triangle in the time domain. A bright green band indicates the centre of each successive symbol, as the display slowly moves along. Ragged upper and lower edges indicate multi-path reception. Fades will show as a darker or narrower section, followed perhaps by a vertical shift in the green band. There will also be a vertical shift in the green band whenever reception starts and the new signal is acquired. The height of this window is equivalent to the length of one symbol (1/baud rate).

On the right, below the Waterfall, the instantaneous Sync Display shows how each symbol is interpreted. A triangular green line with the apex uppermost indicates where the receiving software has determined the centre of the current symbol to be. This indication changes quickly with propagation changes. The red vertical line indicates the average receiver symbol clock position, i.e. the average of the peak in the green line. Sync tracks very quickly and is not affected greatly by noise.

The receiver signal level should be adjusted so that this display shows a full-height green triangle, perhaps a little flattened on top, but not too flattened, and not too small, preferably at least half the maximum height. This is best adjusted using the sound card Recording Control applet level control rather than the receiver audio gain. The height of the green line will change with signal strength, but operation is not fussy as the software has excellent AGC.

Macro Buttons and Control Buttons

Ten Macro Buttons are provided under the TX Window. When you press one of these with a mouse click, standard text is placed into the TX buffer for transmission. You can change both the text content and the labels, and thus the purpose of the buttons. This is done by right-clicking on the button, and editing the text in a small dialog box.

Each one of the buttons corresponds to a Function Key on the keyboard, hence the default names for the buttons. They can therefore also be called up by pressing the corresponding Function Key, which most operators find more convenient, as they then don't have to change focus from the keyboard to the mouse. It is suggested that when the button function is changed, the Function Key number be retained as part of the button name. Note that the F10 Macro is pre-defined to provide a 'delayed end of over', sending the special <EOT> sequence. This Macro can also be edited, so you can easily append your callsign. The message can have several lines of text, and should have at least one new line after the <EOT> sequence. Here's an example:

de ZL1BPU K
<EOT>

The special <EOT> sequence can be used in any of the other Macros, so for example you can easily make a CQ message that stops the transmitter when it's done. The <EOT> sequence is not recognised from the keyboard.

The three Control Buttons to the right, above the Macro Buttons, are Transmit, Receive and Stop. They cause the program to Transmit, Receive, or Pause (neither transmitting or receiving). I think we can all understand these! The active mode has its button greyed out.

Note also that ALT+T, ALT+R and ALT+P sent from the keyboard serve the same functions as clicking on the buttons with the mouse, and can be more convenient.

Be aware that the buttons all act instantly - if you press Receive or STOP while transmitting, transmission will cease instantly, even with data still in the buffer. When you press Transmit again, sending will continue from the buffer where it left off. You can however use a 'delayed end of over' function through the use of the <EOT> sequence in any Macro. The software will then not return to receive until all the text buffer has been sent, up to the point where the Macro was used.

If you press Receive while the transmitter is still busy with transmitting data, you will cut the transmission short. It is really important to wait until all the data has gone before pressing Receive. STOP is useful to prevent the RX Window from moving up and down while you are trying to capture text.

The fourth "button" in this group (bottom left) is the sync averaging slider. Move it to the right for more averaging, and left for less. It has thrwee settings, which correspond to the settings from the Menu. You can click either side of the slider, or drag the slider, but clicking on it does nothing.

Status Line

The bottom line of the window provides status information. On the left, the transmit / receive status, then the sync averaging setting (0 = none, 1 = 'a little', 8 = 'a lot'), and then an indication of how much of the file being transmitted remains to be sent. The next indicator is an interesting "Relative Signal to Noise Meter", which compares the power of the strongest tone against the background. Finally, on the right, for operator convenience, the current local date and time and date as reported by the computer.

The small graphic with diagonal lines at the extreme right of the Status Line is the "handle" used to adjust the program window size. Left-click on this point and drag the window as wide as you need. As the graphics are fixed-size, if you drag vertically, the receive window grows, but the tuning graphics and the Transmit Window remain the same size.

Receiving

The DominoEX program automatically starts in receive mode. The Receive Control Button will be greyed-out. The waterfall and tuning displays will be active. Adjust the audio level (receiver gain at a comfortable level), then use the Soundcard / Input menu item to set the Input Level so the triangular green line just moves on background noise, and there is some sign of the noise on the waterfall display. The program has AGC and audio level is not critical. Tune in a signal, and adjust the receiver tuning until ALL the signal is within the area between the yellow lines on the waterfall.

If more convenient, adjust the waterfall up and down. This can be achieved by left-clicking on the waterfall and dragging the scale display or the waterfall itself up or down. The range is 0Hz to 3000Hz. If your computer speed is under 200MHz, drag slowly. Be aware that the scale of the display changes with the speed setting.

The Waterfall drag affects only the receive signal, not the transmit signal, so work like a receiver RIT. It is best to set the Waterfall start (the scale value at the bottom yellow line) at 1000Hz when tuning around for a QSO, and tune in the signal with the receiver so the lowest tone is close to 1100Hz. That will ensure that the transmitter and receiver are on the same frequency.

If clear text in the Receive Window does not result, check that ALL the signal is between the yellow lines, check that the signal is the "right way up" (correct sideband), and finally check that it is the correct mode! If the signal is tuned correctly, but only the Secondary Text is active, maybe it's a beacon transmission or the operator has fallen asleep...

If the level is too high, the waterfall will smear and individual dots will be indistinct. If the level is too low, the waterfall display will be faint, and poor quality reception will result. Poor print quality can also occur if there is excessive multi-path on the signal. This will be observed on the waterfall as patches of wider than normal tones (vertical stripes or curved lines rather than dots). These effects often occur at a point of fade, and can happen occasionally to frequently. If this happens frequently during a QSO, change to a lower speed as soon as possible, and also be alert for the other operator changing speed (you will hear the tones change). It may also be helpful to reduce the sync averaging at such times. If the signal is weak and especially noisy, increasing the sync averaging may help improve copy.

Hint: DominoEX 11 received in one of the other modes, or vice versa, will give a blurry waterfall, and no sensible print. MFSK16 may look OK on the DominoEX 16 waterfall, but will not sync, the waterfall will show a dominant lowest tone, and there will of course be no sensible print.

As the DominoEX signal drifts, you can adjust the receiver tuning slowly without losing copy, or drag the waterfall in the required direction to centre the signal. You only need to keep the signal between the yellow lines, so tuning is easy.

If your receiver step-tunes in 10Hz or smaller steps, you should not lose copy if you tune very slowly, but if the tuning is in 100Hz steps or greater, it will be better to drag the waterfall for tuning. The waterfall tuning has 1Hz resolution. In order to transmit back on about the same frequency, make sure the bottom of the received signal is approximately at 1100Hz (preferably adjust receiver tuning rather than dragging the waterfall).

Transmitting

While still receiving, you can type in the Transmit Window, cut and paste text, or press Macro buttons, so text will go into the TX Window. This text will be transmitted immediately the transmitter starts, followed by anything you subsequently type in the TX buffer. You can edit text in the buffer before it is sent, even copy, cut and paste, no matter whether the text was typed, copied from the RX window, or from the Macros. You can also do this while transmitting, but you'll need to be fairly quick! Backspace is handy, as it works "over the air" - you can correct text already sent by deleting at the other end!

To start transmitting DominoEX, simply press ALT+T, or left-click the Transmit Control Button. This will now be greyed-out, and the transmitter signal will appear from the sound card, triggering the VOX in the transceiver. Without VOX, the transmitter can be automatically placed in transmit using a hardware transmit control circuit connected to a COM port DTR pin. When correctly set up, DTR goes positive on transmit. The very first time you transmit, there will be a short delay before any tones appear.

Put the software into transmit, and while it idles (no keyboard text sent), adjust the audio level and VOX sensitivity for correct operation. If using the Microphone input for transmit audio, it is best to leave the MIC level setting in the normal SSB position and adjust the transmit power level using the sound card applet. Use the Output Menu to set the Wave Level and the Volume Control to give the correct transmitter drive. Ensure that the sound card output or the transmitter microphone input are not overdriven. This can cause clipping, and assymmetrical clipping results in generation of harmonics within the transmitter passband. The result is a poor sounding signal with excessive bandwidth.

When all the text to be sent has gone (it will appear in the Rx Window) the transmitter will idle, sending 'Secondary Channel' characters, used to send your ID message, and at the same time keeping the receiving station's software in synchronism. As soon as new text is typed, this will be sent in place of the idling. (If you listen to the signal, you won't be able to hear that it is idling, because it is still sending data). Nobody will be able to tell if you are a slow typist!

At the end of an over, wait for the last text to be sent, and shown on the receive screen, and then press ALT+R or left-click on the Receive Control Button. The transmitter will stop immediately, and the receiver will start. Any characters remaining in the TX buffer (the Transmit Window) will remain there unsent until the start of the next over.

The over can also be completed automatically using a Macro. You can set up any of the Macro buttons to contain the <EOT> sequence, which will automatically switch the software to receive when the sequence is detected in the TX buffer. This is handy as it means you can finish typing your over, slip away for a cup of tea, and be back in time to read the incoming text and type the next over! The <EOT> sequence can be used in any Macro, and comes set up for an end of over sequence on Function Key F10. The <EOT> sequence is not recognised from the keyboard.

Mode Definition

This programs encompasses six DominoEX modes, identical except for baud rate, speed and bandwidth, and hence of course performance. The lowest transmitted tone is 1100Hz in all modes.

Modulation

Multi-tone frequency shift keying, using one of 18 tones in a single uniform tone field, spaced x1 baud rate 11 baud and above, and 2x baud rate below 11 baud.

Sync Modulation

No Symbol Sync transmitted. Symbol Sync recovered from receiver transient response. Character sync transmitted as one bit per nibble, designed into the Varicode.

Coding

Characters are varicoded into one-, two-, or three-nibble items, which are subsequently incrementally coded nibble-wise by subtracting each nibble from the previous transmitted difference, in order to remove frequency dependence. Two character sets (Primary and Secondary) are defined.

Necessary Bandwidth

The necessary bandwidths for the most commonly used modes DominoEX 8, DominoEX 11 and DominoEX 16 are 346, 262 and 355Hz respectively.

ITU Emission Designator

The mode is SSB transmitted and therefore rates as J2B rather than F1B, so the modes mentioned above are 346HJ2B, 262HJ2B and 355HJ2B. It is impossible to tell from a reception point of view whether F1B or J2B is transmitted.

Final Notes

DominoEX will be a legal mode of transmission in most countries because it uses narrow-band MFSK, the operating program is publicly and freely available, and the coding technique and alphabet coding are also public domain. There is no hidden encryption, and the alphabets used are ITA5 (extended ASCII) or an ITA5 subset. If your country has more draconian rules, check with your administration - refer them to the DominoEX website, noting that MFSK16, with similar bandwidth and the same character set is already legal in most countries.

DominoEX is the first system available to Amateurs to exploit IFK on HF, and is also the first to deploy managed tone sets. It is not yet the ultimate digital mode - just the beginning! The authors are keen to hear from other developers interested in taking these ideas further, or in achieving some of what has been attempted here in some better way. For example, there are far more efficient ways to achieve improved ISI, and there are character based FEC systems that should be explored. There are developers with better skills and more experience, whose interest we are attempting to arouse with this simple program. We are especially interested to see mainstream developers include this mode in their Windows™ and LINUX™ applications.

If you save this file and its associated images in the same folder as the DominoEX executable, it will be called up by the HELP function within the program.

Technical Details of DominoEX

Why the name DOMINO?

Consider the similarities - can you think of others?

• A field of white dots on a black background (the waterfall)
• Dots on a grid or matrix (frequency and time domain spacing of tone elements)
• Black and white representing things in the digital world
• The two independent ends of the Domino tile might represent the two symbols of each character, or the rendering of data as a numerical difference

We realise that there are shortcomings to the DominoEX program, and would love to hear constructive comments that could improve the mode performance. We are not interested in hearing about how many macros should be added, addition of a logging feature, or other bells and whistles. Just tell us how to make DominoEX work well.

Please pass this program on as-is, and at no charge, to anyone you feel would be interested, but do not reverse engineer the executable code or write something similar but not quite compatible. If you are interested in writing your own improved version, contact the authors for information and advice. We are particularly interested in the development of this technology for Emergency Communications applications. Con ZL2AFP is prepared to make the source code available to genuine developers.

ZL2AFP DominoEX was written by Con Wassilieff ZL2AFP. Ionospheric simulation thanks to PathSim by Moe Wheatley AE4JY. The Help, user documentation, Developers' Pack and web information were written by Murray Greenman ZL1BPU. The original concept was by Murray Greenman ZL1BPU with input from many sources, but nothing would have come of it all without assistance and much midnight oil from Con.

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!

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Copyright © M. Greenman 1997-2005. All rights reserved. Contact the author before using any of this material.  HOME