DominoEX - Frequently Asked Questions


General Questions

Why should I use DominoEX rather than another mode?
It depends on what you are looking for. If you need an easy to use, quick to tune fast response mode that works under poor conditions, there are few other choices. This is especially true if you are a digi-mode beginner, or find tuning these modes difficult. Since DominoEX works better than both RTTY and PSK31, and is faster and slicker than both, is there really any choice?

Why is the DominoEX waterfall display so much clearer than that of other programs?
Because the designers are more clever... no, not at all! Actually it is because the waterfall display is operated synchronously with the incoming data. Most tuning displays do not do this. It also helps that the waterfall has its own AGC.

You will notice that as soon as a signal appears (even if very weak), the noise just instantly disappears, because it is not synchronous with the signal. In addition, if you have the speed wrong, the waterfall will be more furry. Sync is so good that it works on signals you can't hear, and so even these weak signals are clear on the waterfall.

What happened to the old Domino (DominoF)?
DominoF (and DominoG) were development versions, used to prove the technology now included in DominoEX. The new modes are significantly superior, and benefit from over a year of on-air testing. They are faster and easier to use, and sport a full character set as well as secondary text and technically better performance. Just throw out the old software.

Is DominoEX compatible with the old Domino?
No, it is not, unfortunately. There are several points of difference. To have kept them the same would have been to miss out on all the new advantages, such as improved ISI performance, faster text speed and enlarged character set. You should not now use the old programs, or confusion would reign!

How do I tell DominoEX from another MFSK mode?
DominoEX has 18 tones, and is the only mode with 18 tones, but I don't expect you'll be able to count them! The biggest giveaway is that it is the only narrow MFSK mode without an obvious idle condition. MFSK16 starts with a single tuning tone (the lowest) and returns to it when idle. DominoEX does not, since it is never idle. The old DominoF had a downward swooping sound during idle.

You can tell one DominoEX mode from another DominoEX mode by listening to the cadence (the rate of the tones). You can check that the sound is the same as your setting by briefly transmitting and listening to your signal. You soon get used to it.

A certain confirmation is that the waterfall display will be very clear and sharp at the correct speed, and furry if the speed is wrong. If the speed seems correct, but nothing prints, or prints garbage, carefully check the tuning, and also check that you have the correct sideband. No, you can't change sidebands from in the program.

Which sideband should I set my rig to for DominoEX?
The same one you use for SSB would be the best bet. That is what everyone else will expect. That means LSB below 9MHz, and USB above 9MHz, including VHF and UHF.

How does DominoEX compare with Morse for sensitivity?
Morse is pretty good, especially between experienced operators. However, it's not just a matter of sensitivity, as propagation conditions come into the equation as well. Morse actually takes some beating when ionospheric conditions are unstable.

Although dependent on the operator, and a subject of considerable discussion, nobody, experienced or otherwise can copy Morse by ear at reasonable speeds much below -6dB S/N in 3kHz bandwidth (perhaps slightly lower with a good narrow filter). However, without any FEC, DominoEX 8 for example, can be copied 100% at -15dB S/N in 3kHz, while DominoEX 4 achieves about -18dB S/N in 3kHz. In all cases, copy is better by about 3dB when a narrow filter is used. By the way, under these conditions, DominoEX 8 rattles along at 55 WPM!

Computer-read Morse is significantly inferior to DominoEX in all respects, as it suffers badly from signal amplitude errors.

How does DominoEX compare with SSB for sensitivity?
Operators' ears acquire a certain amount of 'training', but even the best operator can't copy SSB at 0dB S/N in 3kHz bandwidth for very long, as it takes considerable effort and concentration. DominoEX works easily down to -15dB S/N, so you can run 10% of the power and still have better copy than SSB, and with none of the effort.

Sometimes DominoEX 11 performs badly on 80m in the early evening, and yet 8 baud is superb, and 16 baud is also good. Why is this?
DominoEX 11 has its tones spaced about 11Hz apart. The receiver can discriminate tones with a resolution of about 3Hz. On 80m during the early evening, in addition to quite marked multi-path, there is often as much as 4Hz Doppler shift. This causes confusion in the receiver. The DominoEX 8 mode has its tones double spaced, at about 16Hz apart, the same as DominoEX 16. The resolution is then 4Hz, which gives a better margin for Doppler, even though the speed is slower.

You will note that later in the evening, 11 baud performs better again. When things are very noisy, DominoEX 8 will be better than DominoEX 11 or DominoEX 16, because the slower symbols give better noise handling.

Why do we have so many different speeds (modes)?
The ionosphere has a wide range of different properties depending on propagation conditions. Obviously the highest speeds would be preferable, but don't always work. By providing speeds in approximate half-octave steps, you can be assured of finding something suitable. The high bands have high Doppler, but lower timing problems. Lower bands have moderate Doppler, except around sunset, but have pronounced multi-path timing problems. LF bands are very noisy, and here and on VHF signals are very weak but stable, and so very slow but very sensitive modes work best. A little experimentation will soon show what's best. Here's a rough guide:

In this context, 'DX' means different things on different bands. For example, on 80m DX means anywhere outside groundwave range; on 20m double-hop or long path; on LF, MF and VHF, any weak signal application. DominoEX works a bit like a manual (stick shift) car - when the going gets tough, change down a gear!

Hint - Print this chart out and stick it on your computer!
Hint - 4 baud is good for QRP beacons on any band. Just drop the beacon message in the Secondary Text and press Transmit!
Hint - When working in a net with local and DX stations, all participants should use the lower of the recommended speeds - but remember these are only a guide.

Why such odd speeds as 11 and 22 baud? What do the names mean?
To make program operation simpler, and the program compatible with as many computers as possible, we have stayed with the four most common standard sound card sampling rates: 8000, 11025, 16000, and 22050 samples/sec. There are 1024 samples per symbol in the faster modes, and 2048 per symbol in the slower modes. We end up with speeds of 8000 2048 = 3.90625 baud; 11025 2048 = 5.3833 baud; 16000 2048 = 7.8125 baud, and 11025 1024 = 10.7666 baud; 16000 1024 = 15.625 baud; 22050 1024 = 21.5333 baud.

In all cases we round the true baud rate up or down to the nearest integer to give the name. For example, 21.5333 baud gives us DominoEX 22. Any the wiser now?

Can I use DominoEX to transmit files or pictures?
At present, no. You can transmit a text file (with or without error correction) to the other operator's receive screen, but that's all. There are plans to add file and image transmission, and a simple protocol for each has been defined, but at present there is no functional software to support them.


Program Related Questions

When I change speeds, the tones come out wrong for a few seconds. Why is this?
It should be that the transmitted data is flushed when you change speeds. This would avoid the problems. However, in the interests of program simplicity, this isn't done at present, so samples remaining in the buffer when the transmitter stopped are sent first, and of course at the new speed the samples are wrong. Don't worry, nothing you typed is lost.

A related problem (nothing in the buffer) means that when you FIRST transmit after starting the program, nothing happens for a second or two. Don't worry, no data is lost.

There seems to be a problem with the RX screen. Sometimes my transmitted text shows as a random series of characters up the left margin, and the guy at the other end sees the same. Why is this?
We wish we knew! It is an idiosyncracy of the way Windows™ 'Rich Edit' boxes work, and something to do with the process of transferring text from the keyboard buffer to the transmitter queue. For some reason 'LF' characters are substituted for the real data. It has proved to be a difficult bug to fix as it happens only occasionally, and never at all on some computers.

To avoid this problem, it seems to be best to leave the typing 'insertion point' focus in the transmit window. The problem is more likely to occur if you cut and paste text, change focus to another program, or click in the RX window. When the problem happens, the most reliable solution is to close the program and restart. Sometimes the problem goes away if you change back to receive and then transmit again, but all the untransmitted text should be cleared.

Sometimes the Function Keys don't seem to work. Why is this?
This is one of the 'features' of the Windows™ operating system, especially XP. You probably inadvertently pressed the 'ALT' key at some point. Just press the Function Key again and it will probably work.

Why do I lose changes to some settings if the computer crashes?
The setup (including the MACRO contents) is kept in a file which is saved only when you close the program. If you make changes you want to keep, and there is some risk of the computer crashing, close the program after making your changes, then reopen it. Some options always revert to defaults - operating mode and sync filtering, for example.

What automatic functions can I use in Macros?
There is only one automatic function available in this demonstration program: the <EOT> 'delayed receive' function. This can be included in any Macro, provided it is on a new line at the bottom of the Macro, and followed by two new lines. There are no plans to add further automatic functions.

Sometimes the program won't recognise the sound card, and I've found that there are two programs opened! One is hidden under the other. Why is this?
There is no mechanism in this relatively simple(!) program to prevent multiple instances from being opened, and of course the second instance is placed on top, and can't access the sound card. Simply close this one and use the other. It is best not to launch two instances. This is most prevalent if you have a shortcut to the program on the tool bar and inadvertently click twice. It is best to place your shortcut in the menu structure, or put the shortcut on the desktop.

I seem to be having a problem with PTT when I send a file. What's happening?
There is a poorly understood and inconsistent interaction between the Windows functions to open a file and to open a COM port. On most computers and operating systems there is no problem. However, due to a combination of circumstances sometimes it is found that while when transmitting and a file is then selected to be transmitted, everything goes as expected, but when the file is selected before the transmission is started, the transmitter drops out.

The best solution is to use VOX if you meet this problem, or simply select the transmit switch on the rig before sending a file. You may also find that PTT works if you always do things in the same order. You could also avoid sending files, of course.

Be aware that selecting a file for transmission DOES NOT automatically start the transmitter. You still have to press ALT+T or use the Mouse TX button.

With FEC on, there seems to be quite a delay before text I type appears on the screen. Why is this?
When FEC is used, the data is fed through a coder which is 7 bits long, followed by an interleaver (to jumble the bits) 40 bits long, and so a delay is introduced, At the receiver, the de-interleaver is also 40 bits long, while the Viterbi decoder works back about 15 bits. The total delay is about 4 seconds at 11 baud.

In a related problem, when you tune in a signal with FEC, it will take several seconds for viable text to appear. You will see the Confidence Meter rise before the text appears.

With FEC on, does the transmission delay mean some characters are lost at the end of the over?
Yes, certainly there is this risk. When you stop typing, leave a few seconds for the TX buffer and coders to be flushed before going back to receive. If you use VOX or PTT control, the easiest way to achieve this is to use the RX macro which sends the sequence. The transmitter will not stop until this sequence has been flushed from the coder and transmitted. You can also add this sequence to any macros you define.

With FEC on, is the signal any wider?
No, the signal width stays the same with FEC on, as the modulation is the same. The typing speed will be halved.

With FEC on, is the signal encrypted, and so illegal on ham bands?
The FEC coding uses two standard NASA algorithms, which are public domain (we use R=1/2 and K=7). The interleaver is also public domain (published on the MFSK16 web site, we use L=4 by default). There is no encryption. The FEC mode is quite legal - the same encoding is used in MFSK16. Anybody with the DominoEXFEC software or a recent version of MultiPSK can copy the signals.


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