Getting Started with Fuzzy Modes

This page is for those who are totally bewildered by the whole concept of Fuzzy modes such as Hellschreiber,
and don't know where to begin - so begin here!. Most of this information is in Q&A format.

Download PDF Getting Started Manual (165k)


Why should I consider Hellschreiber?

Hell is a very old mode, but was well thought out in the first place, so has very good performance, even by modern standards. It is suitable for live QSOs, and is ideal for rag chewing, being very slick and easy to use, and easy to tune. Hell is reasonably sensitive, and very noise and interference immune, since the human eye/brain processor is used. With modern DSP processing, "Fuzzy" reception and presentation, the mode is now better than ever.

There are times when other favourite digital modes will not perform adequately. For example, PSK31 will not work when there is excessive polar flutter or ionospheric Doppler. RTTY suffers very badly from selective fading and multi-path. Feld-Hell is not particularly affected by these problems, although it is affected by multi-path reception to some extent. The smart ham chooses the correct mode for each occasion.

Hellschreiber modes are for real person to real person, real time, point to point contacts. There are no Hell repeaters (except the moon and some Oscar satellites), no Hell bulletin boards, and no automated operation. Hell is for rag-chewers and DX operators. Hell is easy to set up and easy to tune, requires a minimum of equipment, and so is an ideal mode for beginners.

Is Hell a digital mode?

Well, in so far as it is transmitted by a computer, and on-off keyed, then maybe it is, just as Morse is. When it comes to the regulations and operating rules in your country, then focus on what is transmitted - it's a digital transmission.

However, in Hellschreiber, analog dot timing is important, and linear transmitter operation is important to preserve the careful envelope shaping (and sometimes grey dots too), so the transmission really contains analog data. Without any question the receiving process is an analog process, since the display is grey-scale and the human eye and brain are used to interpret what is received.

So really, the overall answer is NO - Hell is a Fuzzy mode, half way between digital and analog, just like Morse. Unfortunately Hell is often lumped together with digital modes because a computer or electronics is usually used to generate it.

If you ask the FCC, they will tell you it is a digital mode (even they are not sure). Their point of view is useful however, as it does mean that the US Hell operators are permitted by this ruling to use the same parts of the bands that the rest of the world uses. Without this ruling US Hell would be stuck in the SSB sub-band.

Just what is a "FUZZY" mode?

We describe Fuzzy modes as those which use the human skills of pattern recognition, noise rejection, and context interpretation to the maximum. To do this, the human has to be presented with the signal as received, without any electronic attempts at interpreting the data before presentation.

For this reason, Fuzzy modes are always uncoded. This means that the data to be sent is transmitted in a way that directly represents the data, not a code which can be translated into the data. Thus Fuzzy modes are less efficient than digital modes (from the point of view of bits per character), because they contain more redundancy, which is used to provide better interpretation of the received information. See the Philosophy of Fuzzy Modes page for more information.

You might consider Fuzzy modes to be half-way between digital modes and analog modes. Examples of Fuzzy modes are Morse, Hell and Facsimile. Television and SSTV are very close to being Fuzzy modes, but usually have digital synchronisation.

There is a whole section on this site about Fuzzy Modes.

There seem to be many different Hell modes - what are they all?

There are indeed several known on-off keyed Hell modes, but only the most famous Feld-Hell is still in regular use. Then there are the frequency domain modes: Finally there are the modern "designer" modes - specialised modes designed for high performance under different conditions - See the Hell Formats page for details.

Which Hell mode should I operate?

For HF DX, you should use Feld-Hell, or FM-Hell, as almost everyone on HF uses either the IZ8BLY sound card software, or MIXW, which both offer these modes. There are even a few real Hellschreiber machines still in use! If you use other software, it must be compatible with the Feld-Hell 122.5 baud (2.5 char/sec) standard. Once you have established contact, you can negotiate which mode in which to continue the QSO. PSK-Hell and FM-Hell from the IZ8BLY software are perfect for long distance DX.

Some operators will happily try MT-Hell with you, provided you use a compatible mode. MT-Hell is especially useful on HF if signals are strong but there is bad lightning interference or multi-path reception. It is also very effective to change to MT-Hell to combat on-frequency carriers, Morse or Pactor. Be aware however that not all C/MT-Hell versions are mutually compatible. G3PPT MTHKBD2 is reasonably compatible with the EVM C/MT-Hell, as is the latest IZ8BLY version. There is not much choice of software here.

For LF, MF and low HF bands, almost anything goes, so long as you can find someone to work. The most common modes are Feld-Hell, FM-Hell and Duplo-Hell. Because low HF and MF are so noisy, MT-Hell can be effective, with FM-Hell for long distances. On LF, S/MT-Hell with transmission widths of about 1 - 4Hz are useful for beacons.

All Feld-Hell software transmits compatible signals,(the standard is 122.5 baud, 2.5 characters/sec) but this is not true of MT-Hell. For example, IZ8BLY V 2.6 and above C/MT-Hell is not compatible with other versions since a different (time domain) receiving technique is used. Here is a list of compatible MT-Hell modes:

Where should I operate?

This is a thorny question. First of all, you MUST operate within the rules for your country, and within the guidelines set down by the IARU for your region. Here are some points to ponder:

Hell Facts and Fiction
  • Feld-Hell is on-off keyed CW, just like Morse
  • Feld-Hell is uncoded and human readable, just like Morse
  • The IARU "CW" recommendations do not mean Morse, they mean "CW" (continuous wave)
  • Feld-Hell is narrow band (300-350 Hz), with an identical spectrum to 80 WPM Morse - FM-Hell is much narrower (150hz)
  • Many Hell operators believe that Feld-Hell should be used in the IARU recommended CW segments of the HF bands, with Morse and other CW modes.
  • It is widely believed that "CW" means "Morse Code". This is incorrect - it means "Continuous Wave" and the term can be applied to any on-off keyed mode.
  • Some operators consider Hellschreiber to be a "digital mode", but by the same definition (on-off keyed carrier), so is Morse
  • Hell is transmitted as a digital mode, but is also an analog mode, and can sometimes even send grey dots!
  • Hellschreiber operators suffer the same QRM as other CW modes, especially on 20m.

We believe that Hell operators can quite legitimately operate Feld-Hell anywhere where CW modes are permitted, but check your local regulations, which may specifically allow "Morse"and not "CW". Hell operators should of course keep clear of Morse stations, and from each other by at least 500 Hz, and especially keep clear of the QRP Morse area at 14.059 - 14.061MHz. Most operation on 20m is now around 14.072 - 14.075MHz. Obviously we should expect the IARU to clarify the situation as time goes on.

Reasoned discussion of where best to operate would be welcome. The proper forum for this debate should presumably be the Hellschreiber Reflector.

Where will I find Hell signals?

These are frequencies in current use, and should be in line with the IARU recommendations. Frequencies are quoted in MHz and are generally the indicated USB dial frequency. Any corrections or additions to this information should be sent to the author.
Current Operating Frequencies
80m    3.575 (Region 1) 3.559 (Region 3)
40m    7.030 -  7.040
30m   10.135 - 10.145
20m   14.065 - 14.080 (most operation around 14.075 MHz)
17m   18.101 - 18.107
15m   21.063 - 21.070
10m   28.063 - 28.070 and 28.100 - 28.110 (novice)

Frequencies quoted are for actual transmitted carrier frequency.
Check the operating rules for your country or region.

What does "actual carrier frequency" mean?

Confused about how frequencies are quoted? So are many folk! It would be easy to quote just the reading on your receiver dial, but it isn't that simple, because the display will differ from those of others, depending on your rig, your software, and your settings. The ONLY thing you can rely on is the actual transmitted frequency. Fortunately for us, Hellschreiber generally transmits only one frequency.

Here's an example. You use the IZ8BLY software, and your tone frequency is set to 980 Hz. Your transceiver is on USB, and the RIT is off. Your display says 14.0630 MHz, and you have a Hell signal tuned in exactly on the tuning display. The transmission carrier frequency will be 14.0630 MHz + 980 Hz = 14.06398 MHz. If you push the "TUNE" button (on the IZ8BLY software), that's the frequency you will radiate, which you can check with your frequency counter (you do have one, right?).

The method of determining the carrier frequency and the display frequency depends on the mode, but the guideline for Hell is as follows:

What Class of Emission is Hell?

On-off keyed Hellschreiber (Feld-Hell) generates double sideband AM, has a single modulating channel without subcarrier, and is a Facsimile mode, hence it is A1C. When transmitted via an SSB transmitter it will be J2C. The full definition is 350HJ2C.

PSK-Hell might be P1C. When transmitted by an SSB transmitter (as it always is) it is J2C,or 150HJ2C. FM-Hell is probably F1C. For example, FM245 would be 150HF2C.

Sequential MT-Hell (S/MT-Hell) is multiple tone MFSK with 5 or 7 channels of information, so is F7C. When transmitted via an SSB transmitter it will be J2C, just the same as Feld-Hell! At 30 Hz tone spacing, the full definition will be 250HJ2C.

Concurrent MT-Hell (C/MT-Hell) involves 7 or more concurrent subcarriers transmitted via an SSB transmitter as J2C. As transmitted by the G3PLX software, the full definition will be 250HJ2C.

Multi-tone Hell is considered a single "channel", because the data carried on each subcarrier tone frequency is not independent of the other tones. For the record, 80 WPM Morse, on-off keyed, is A1A, or when sent via an SSB transmitter is J2A - full definition 350HJ2A, and is spectrally identical to Feld-Hell.

How about DXCC - is Hellschreiber recognised?

Hellschreiber is currently recognised by the ARRL DXCC Committee as RTTY! Considering that the name of the wartime Hell machine "Feldfernschreiber" means "field teleprinter", their ruling is understandable. In time maybe they will understand that Hell is not a digital mode, and give it a classification of its own.

Is Hellschreiber legal?

Hellschreiber was recognised as a distinct mode by the CCITT well before the Second World War. In most countries Hellschreiber is legal if RTTY is legal. In many countries any mode is legal if the technology is public domain or the equipment freely available. If in doubt, check with your local licencing authority.

For US Amateurs, consider the following recent comments. First, from Steve WB8IMY (Technical Editor, QST):

"As to the nature of the mode (digital or image), the FCC admits that the distinction is unclear. However, they are aware that most of the activity is taking place in the digital sub-bands and that most of the amateur digital community appears to consider Feld-Hell to be a digital mode. So, they seem content to classify Feld-Hell as digital."
From Chris Imlay, W3KD, ARRL General Counsel:
"Discussions with FCC staff concerning the legality of Hellschreiber resulted in... (classification J2B) ...The legality of other amateur modes should be determined by the same method."
From Paul Rinaldo, W4RI, ARRL Technical Relations Manager:
"US amateurs may transmit Hellschreiber in the RTTY/data segments using single-sideband transmitters. J2B is the appropriate emission symbol".
The FCC accepts that Feld-Hell (and its variants) qualify as legal modes under Part 97 of the FCC Regulations section 97.3(c).

How do I describe the mode in my Log Book, or on a QSL card?

I'd put down "Hell" or Feld-Hell", since J2C is a bit vague. FH, C/MT and S/MT will work too.

What software do you recommend?

This decision depends on your computer as much as anything else. See the Software page for suggestions.

What computer do I need?

For the software suggested, you need a PC. Not an Archimedes, BBC, Commodore, Mac ... or ZX Spectrum. Apart from the shareware program Multimode by Black Cat Systems for the MAC, there is no recent software that I know of for any other modern computers -let me know if you know something I don't! Any sort of PC will have its uses, from a 10 MHz XT upwards. There is also a choice of software for LINUX.

It is quite practical to use an old PC or an older lap-top for Feld-Hell transmit and receive.

What else do I need?

All Hell modes and software need more than just a PC - they require some sort of interface to the real world. It may be as simple as a speaker taped to the microphone, or a Hamcomm interface, but virtually all software uses a standard PC sound card. You will then need cables to suit your radio and sound card.

Everything you need to know about setting up the IZ8BLY software can be found in the help file. The business of setting up the computer and cables is described in the downloadable Getting Started document.

Can I use a Baycomm modem (or some other interface) for Hellschreiber?

In a word, no. Stick with the PC sound card.

Are there any Hell contests?

For many years the Hell contest run by the DARC has taken place on the first full weekend in October. It is followed by a VHF contest on the following Thursday evening. Unfortunately the rules and operating frequencies preclude any real international action in the HF contest. More information is available from:
   DF5BX, Werner Ludwig
   Postfach 12 70
   D-49110 Georgsmariehutte
   Germany
This contest is on 80m, 40m and VHF only, so is biased towards European operators. We hope that the rules will be changed, or another contest introduced, which encourages DX operators to take part.

Hellschreiber Activity Day There is an informal "uncontest" on ALL BANDS from DC to daylight, run on the last Saturday of the 1st, 4th, 7th and 10th months. (January, April, July, October). There are no rules, but a self-scoring system is devised to add interest. Details are sometimes posted on the Reflector, as are the results. This is an excellent DX opportunity. Special calls and rare prefixes often appear! There are also occasional multi-mode contests which have a Hellschreiber section.

Why does the received text slope sometimes?

The slant is caused by the receiving dot scanning or sampling rate being different to the transmitting dot rate. Old mechanical machines are governed mechanically, and actually have an adjustment to minimize the slant on received text. If the receiving equipment runs slow, the text will slope down, and if it is too fast, it will slope up. The picture below is a photograph of a tape received on a mechanical Feld-Hell machine from the 1940's, using the protocol we still use today, and demonstrates an error of about 1 in 200. The whole purpose of printing the text in two rows is to allow the characters to be easily readable with excessive slope.

Text received by the same equipment that sent it will always appear without slant. For this reason, "local copy" of your signals will always look correct. Modern systems, which use a PC sound card, have the sampling and dot timing controlled by a crystal oscillator on the sound card, and should therefore be much more accurate. If the reference is within 1 in 104 the slant will be almost unobservable (this represents the height of one dot in 200 characters). From time to time you will see transmissions from badly adjusted systems with more error than this. They may be from poor quality sound cards, or from PCs running the LA0BX software, where the actual PC system clock is not correctly calibrated.

Does it really matter if my text slopes?
No, it does not. Your text will always be readable. However, everybody will keep telling you that your text is sloping, and almost every signal you see will appear to be sloping.

How do I know who is right and who is wrong?
Take a vote - most signals you see will be close, so if everyone slopes the same way, it is you that has the problem! If you use IZ8BLY Hellschreiber or MIXW, there is a simple way to use a standard time/frequency station as a reference.

Can I recalibrate my sound card?
It is not really practical to do this in hardware, and replacing the sound card is both expensive and not guaranteed to fix the problem. It has been found that many of the older cards are better than the new ones! Good software will offer a software sound card calibration facility to correct sloping text.

You can also use this feature to work out what correction factor an other operator should be using. Note your normal calibration setting, change the setting so that the other station is printing straight, then subtract your normal correction factor from the new value (observing sign), and tell him this number with the sign changed. The sign should be opposite to yours.

Why don't we use an asynchronous system to avoid the slope problems?
The asynchronous systems, L-Hell and GL-Hell, allow the receiving machine to align itself for every character using a start-stop system. The trouble is that the synchronism information is prone to noise and incorrect interpretation, so does not allow the system to operate as a truly Fuzzy (human readable) system. These systems were designed for land-line use. Printing everything twice is a small price to pay for the enhanced performance of a truly Fuzzy mode.

How do I operate?

Hell operating procedure is very like Morse procedure, and not too dissimilar to RTTY or PSK31 procedure. It's very straightforward. Most of the same abbreviations apply.

What is the Duty Cycle of Hell?

Feld-Hell has a much lower duty cycle than most modes - even Morse. This is because there is a large field of untransmitted white dots around each character. On average, there are only 61 dots transmitted in every word, which potentially contains 294 dots, so the duty cycle is only 21%. This has major benefits for the transmitter, which will stay cooler.

Stated another way, the transmitter peak-to-average ratio is very high. This means that the mode offers impressive noise rejection performance. However, it is important to realise that the meters on your rig will not realistically indicate the actual peak power output, and it is important to make sure that the transmitter will handle the peaks, and is tuned up for them. By comparison, the duty cycle on Morse is about 46%. The duty cycle on S/MT-Hell is between 50 and 80%, and on C/MT-Hell about 80%. PSK-Hell runs about 90% and FM-Hell 100%, but they don't need much power.

Technical Hints

Other Digital Modes

While this site is dedicated to the Fuzzy modes, digital modes are fun to use and experiment with too. Many of them can be operated using the same hardware described above.
Copyright © M. Greenman 1997-2005. All rights reserved. Contact the author before using any of this material.
home HOME