Digital Symbols

SUBJECT: SYMBOLS FOR DIGITAL MODES USAF MARS: ROGER B. HUGHES / AFA9HR / AFF9TD Quick Guide to Documentation on Symbols for Digital Modes Objective The idea of this quick overview is to explain what the symbols used in digital modes such as K and AR come from and how they are used. 1. Overview of the symbols used in CW and radiotelegraphy. 2. Overview of the symbols used in radio teletype (RATT) and other more modern modes such as MT63 and MFSK. 3. Reference to the Allied Communications Procedures publications that contain the relevant information for use within USAF MARS. Topics for Reference 1. Frequently on amateur circuits that use digital modes, such as PSK31, different techniques have been used to have a protocol that works under specific circumstances, e.g. KK is frequently used in amateur circuits to indicate “over” as the double character is most likely to be well interpreted when working on marginal links under marginal power. In military circuits, this is unacceptable, the correct signal is a single K meaning “over”. 2. In summary, we have the following: • K — “over” — all transmissions end in either K or AR, never both • AR — “out” — never use AR and K together on MARS circuits • AS — “wait” — short time wait, say up to 15 seconds • AS AR — “wait out” — wait longer than 15 seconds 3. All the operating symbols are listed in the ACP set of publications which may be found on http://jcs.dtic.mil/j6/cceb/acps/ 4. ACP 125(F) is for radio telephone and all MARS operators should become familiar with it. Anything questionable in terms of procedures can usually be answered by reference to this publication. 5. ACP 124(D) for radiotelegraph, which goes into detail on all the prosigns. Note that in CW, that some of the prosigns like AR are actually sent as a single character and are usually written with a bar over the character combination to PAGE 1 OF 4 DURATION: NOVEMBER TRAINING SUBJECT: SYMBOLS FOR DIGITAL MODES USAF MARS: ROGER B. HUGHES / AFA9HR / AFF9TD do this. In modern texts, the bar cannot be easily done in current Word Processing software, so people tend to use an underline instead of an overline, i.e. writing it as AR; another alternative is to brace it as follows <AR>. Of course, if you are not using CW, then just sending the text letters will achieve the right effect. But suppose you are sending CW and you are using a computer to send it? Then you need to define characters that have the right “sound” to equate to AR, i.e. to equate to the letter A followed immediately by the letter R without the usual inter-character space of three dits duration, but just a single dit duration space. In MixW, the international character with the same dot-dash combination as AR is used, namely +, so instead of typing AR, which will give you .- .-. which is AR rather than <AR> type +, which will give you .-.-. which is a true <AR> or AR or AR One should always take great note of which prosigns do have a line over them in CW, as these must be sent as a continual single character when using CW. It is very confusing to a CW operator to hear the letters sent separately as it won’t sound “right”. A computer Morse program receiving “.-.-.” will typically print this not as “+” but as “<AR>” with the braces around the <AR> to indicate that it is a code group. In Fldigi, the current keyboard character for generating <AR> during transmission is “}”, which is the right curly brace. If you have messages that have been prepared digitally for other modes of transmission and wish to use computer generated CW to send the text, do please make sure that the “plaintext” prosigns of AR and BT are changed to the characters corresponding to <AR> and <BT> in your Morse code software. <BT> in both MixW and Fldigi is “=”. In CW nets, one should also note the use of the II character as a separative sign. This is simply two I’s with the usual inter-letter space. It is used before and after the precedence of the message, before the FM prosign, before the TO prosign and before other prosigns in the address part of the message. e.g. look at the following for a correctly formatted message as sent in CW: DE AFA9HR NR 123 II R II 230100Z NOVEMBER 2009 II FM ROGER / AFA9HR / CA II TO ALL 9R1 STATIONS II INFO DENNIS / AFA9AY /CA BT message text here BT K PAGE 2 OF 4 DURATION: NOVEMBER TRAINING SUBJECT: SYMBOLS FOR DIGITAL MODES USAF MARS: ROGER B. HUGHES / AFA9HR / AFF9TD Now, you might be thinking, that those II characters make things tricky. Well, normally when writing or typing the text, when receiving it manually, the II would be written as a short dash, so the preceding message would look like this: DE AFA9HR NR 123 - R - 230100Z NOVEMBER 2009 - FM ROGER / AFA9HR / CA - TO ALL 9R1 STATIONS - INFO DENNIS / AFA9AY /CA BT message text here BT K Because there is no nice formatting built into Morse, the II separative sign is extremely useful in helping one be ready to receive Important Information such as the precedence, date-time-group, from address etc. The separative sign is also useful when acting as a net control and you want to acknowledge messages from different stations, or if you are joining a net and have messages for individual stations of same or different priority, e.g. DE AFA9HR ZBO 1R AFA9AY II 2P AFA9PF II 1R AFA9HS K 6. ACP 126(C), which is the radio teletype manual, has some very good descriptions of prosigns and their usage from a radio teletype perspective and was also written a few years after the radio telegraph manual listed in the previous paragraph, so is a little more modern in style. Both are excellent documents. However, you will note that the radio teletype manual does mroe frequently consider how to sectionalize large messages. 7. ACP 131(F) is the operating signals document that gives all the Z codes for military frequency usage as well as Q codes in a very comprehensive listing. Remember, don't ever use Z codes on amateur frequencies, only Q codes. On military frequencies, use a Z code if one exists with the right meaning in preference to using a Q code of equivalent meaning. If no Z code exists, then use a Q code. It should be noted that a huge number of the Z codes were specifically designed for use with Morse code (CW) transmissions, as CW was a predominant mode of military communications in weak signal conditions for many decades and having codes greatly speeds up the communications efficiency. A large number of these codes are no longer used in practice and a greatly reduced subset can be PAGE 3 OF 4 DURATION: NOVEMBER TRAINING SUBJECT: SYMBOLS FOR DIGITAL MODES USAF MARS: ROGER B. HUGHES / AFA9HR / AFF9TD used for MARS usage. The advantage of this document is in the explanation of the numeric quantifiers that can be used to good effect with some of the codes to describe specific conditions such as closing down temporarily or immediately. One final note with regard to use of operating signals contained in Z codes and Q codes is warranted. Whilst Z codes and Q codes are very useful for CW and are also useful for some of the slower modern digital modes that work under extremely low signal to noise (S/N) ratios of down to -12 dB and lower, they should never be used on voice circuits as plain language is the only thing authorized for voice circuits and, I would argue, neither should they be used on very fast digital modes, unless you are an extremely slow typist. Plain language is much better to understand and if a single letter of plain language gets garbled you can decode the meaning quite easily without getting things wrong, a single letter wrong on a Z code and one can get a different meaning. Hence the importance, if using Z and Q codes of sticking to what is normally used in a typical contact in the typical sequence to ensure that rapid understanding is achieved. PAGE 4 OF 4 DURATION: NOVEMBER TRAINING.

Load more