Talk:Radioteletype

Could someone who knows adds some information on the history of RTTY, e.g. when it was first used? I know that Baudot codes have been around since the 1870s; is RTTY of similar provenance? -- Cabalamat 01:04, 25 September 2005 (UTC)

User:Eyreland added a lengthy section named History but I removed it, as it seemed to be a copyvio ([1]). Mysid 10:35, 21 March 2006 (UTC)

I've added some details to the history of RTTY. More to follow as I find time to research my files for original documents to reference. Wa3frp (talk) 16:00, 16 December 2007 (UTC)

The history section seems inaccurate based on History of radio, because it is hard to square the dates in that article with an 1840s or even 1870s beginning to radioteletype. Put simply: this article needs to explain how there could be radioteletype before there was radio. Brianwc (talk) 04:16, 3 September 2009 (UTC)

Hi! Thanks for your question and comment. Please review the first sentence in the second paragraph whiche reads "...Radioteletype evolved from these earlier landline teleprinter operations..." I am using the first two paragraphs to show how radioteletype evolved from landline teleprinter operations. I feel that this is key to a full understanding of the history of radioteletype. Does this help? Thanks!Wa3frp (talk) 04:19, 5 September 2009 (UTC)

Would a list of common/popular rtty frequencies/stations be appropriate?

Please discuss... 66.28.178.67 17:31, 27 September 2007 (UTC)

It would certainly be good to include categories of stations, types of transmissions, modulation types, or long term stations and frequencies that have been published somewhere. Former stations such as news broadcasts are no problem. Original logs are out of place here because it is original research. It is best to format the information as text in paragraphs rather than a list. Graeme Bartlett 21:04, 30 September 2007 (UTC)

There are very few non-encrypted RTTY stations today, most notable being the German Weather Service. If there is no objection, I shall add the frequencies and callsigns.

Sv1xv (talk) 16:17, 7 January 2008 (UTC)

It is my opinion that this is useful information and should be posted. However, it also needs to be checked often and kept current. This is because no information is better than incorrect information. Be sure to also post the shift and speed. I believe that the German Weather Service uses 425 Hz shift and 50 baud. Wa3frp (talk) 12:41, 8 January 2008 (UTC)

OK, I just added this information plus a link to the source (DWD web site). Sv1xv (talk) 18:58, 8 January 2008 (UTC)

How it works

I propose that this section is moved immediately before "Technical Specification". It must also be expanded to include a very brief description of parallel to serial conversion, numbers shift, start/stop bits. Information duplicated in "Technical Specification" should be removed.

Is there any information or refernece to the "6-bit ITA2" alphabet and the system using it ?

In addition to "RYRY..", the "THE QUICK BROWN FOX...." test sequence should be included.

Do you propose any other additions and changes?

Sv1xv (talk) 08:00, 11 January 2008 (UTC)

These all all very good improvement ideas. The only reference that I've located so far on "six bit ITA-2" comes from http://lycos.com/info/baudot-code--characters.html?page=3 and I'd suggest that any reference to "...THE QUICK BROWN FOX..." also have a link to http://en.wikipedia.org/wiki/Pangram.

Wa3frp (talk) 20:02, 11 January 2008 (UTC)

I just added a "Technical description" section, but did not yet touch the existing "How it works". Your comments please?

Sv1xv (talk) 19:41, 12 January 2008 (UTC)

WA3FRP, thanks for the corrections and improvements. Next step is to copy some information from "how it works" into "technical description" and then delete the former subsection. Sv1xv (talk) 09:53, 13 January 2008 (UTC)

The following block of text was merged with "Technical description" and then deleted:

“ RTTY uses a variety of different modulation methods, of which frequency shift keying is the most common.

The FSK RTTY signal starts at the teleprinter as groups of dc impulses, known as marks and spaces. Each group represents an alphanumeric character or a function. As the operator types characters and functions on the teleprinter, the connected originating transmitter's carrier is shifted by a predefined frequency, usually 170 or 425 Hz. At the receiving end, the shifted carrier is detected and the audio output is normally fed to an external Terminal Unit ("Demodulator") which converts the audio signal to dc impulses which operate the teleprinter. These FSK signals can be heard on a communications radio receiver equipped with a BFO (beat frequency oscillator), and have a "beedle-eeeedle-eedle-eee" sound, usually starting and ending on the high-pitched tone.

The most common test-signal is a series of "RYRYRY" characters, as these form an alternating tone pattern exercising all bits and are easily-recognized.

* Coding used is typically 5-bit ITA2 code (also known as the Baudot code), which is asynchronously with start and stop bits. * At least one common RTTY system uses 6-bit ITA2 character codes. * More modern systems use 7-bit or 8-bit codes, e.g. ASCII.

Many RTTY operators had equipment which featured paper punch-tape readers. The operator would type the message on the TTY keyboard, which would punch the code into the tape. The tape could be re-done as desired, then transmitted at a steady, high rate, without typing errors. A tape could be reused, and in some cases - especially for use with ASCII on NC Machines - might be made of plastic or even very thin metal material in order to be reused many times.

”

Sv1xv (talk) 20:24, 13 January 2008 (UTC)

looking very good. Much more information and better flow than before.

Russ Wa3frp (talk) 02:00, 14 January 2008 (UTC)

De VA2JOT QUOTE: The line output of a teleprinter can be at either digital logic levels (a 5V signifies a logical "1" or mark and 0V signifies a logical "0" or space) or line levels (-80V signifies a "1" and 80V a "0"). When no traffic is passed, the line idles at the "mark" state.

Seems to me there were either 20ma or 60ma DC circuits. Applied voltage was chosen depending on the loop resistance. At least, this how the local loop was engineered in North America on Bell System TTY circuits. Loop closure by the TTY was Mark, loop open was Space. The signalling was based on current flow, not the applied voltage.

Long loops or toll circuits used 43A1 carrier channel units (FSK). At the subscriber end, a subset equipped with a 43A1 unit converted the FSK to 20 or 60ma loop current. —Preceding unsigned comment added by 142.169.28.200 (talk) 13:42, 2 September 2009 (UTC)

Slow by modern standards

The statements in this section are not very accurate, RTTY is not a very robust mode (SITOR-A and PACTOR perform much better) neither a very slow one (150 baud is not bad). Lack of error detection and correction is its main drawback. Most users did not change from RTTY to some other mode, they just abandoned HF radio links in favor of landline and satellite (press, AFTN, etc). I propose that this section is corrected and merged with "How it works".

Sv1xv (talk) 08:00, 11 January 2008 (UTC)

I agree with your comments here as well.

Wa3frp (talk) 20:03, 11 January 2008 (UTC)

I changed this section to "Comparison with other modes" and tried to reflect the foregoing discussion.--Albany45 (talk) 03:52, 19 March 2010 (UTC)

I read your changes and they are an improvement over what was there before. I do have a question about RTTY FSK. Could this simply be RTTY? I see RTTY as FSK or AFSK and there is no discernable difference between the two to the receiving station.

For example could "...For its transmission speed, RTTY FSK has low spectral efficiency..." be edited to "...For its transmission speed, RTTY has low spectral efficiency..."?

And, could "...The typical FSK signal with 170 Hz shift at 45 baud requires around 250 Hz receiver bandwidth, over double that required by PSK31..." be edited to "...The typical RTTY signal with 170 Hz shift at 45 baud requires around 250 Hz receiver bandwidth, over double that required by PSK31..."?

While "RTTY" is often used to imply the mode designation F1B, other emission modes can be used for radio teletype. (I define RTTY as transmission of Baudot code via radio in such a way that you could connect a physical teletype machine. I think this is consistent with the 2nd definition in the main article?) As you note, AFSK (A2B) has been used. Earlier, some attempts (commercial, not amateur, I think) were made with on-off keying, which would probably be A1B. (We could include a reference to Types of radio emissions.) It might be better for this section to refer to "FSK RTTY" instead of "FSK". On the other hand, FCC 97.307 makes the "mistake" of saying "RTTY" instead of RTTY FSK! --Albany45 (talk) 18:43, 22 March 2010 (UTC)

First of all, the only reason that on-off keying (A1B) was used to my knowledge was amateur, before 1953, since frequency shift keying was not legal. Do you know of a commercial use of A1B? Second, only F1B and A2B were, and are, the only two modes that I'm aware that had widespread use on RTTY. I'd say that the FCC s correct in this case. FSK RTTY and AFSK RTTY is RTTY. I use FSK but I'd say that I've never been able to tell a correctly adjusted AFSK signal from an FSK signal. —Preceding unsigned comment added by Wa3frp (talk • contribs) 19:21, 22 March 2010 (UTC)

You may be right about OOK/A1B, we need further research. After demodulating AFSK and FSK, you have the same result, but if you listen to FSK with an AM detector, you get nothing useful.--Albany45 (talk) 16:23, 23 March 2010 (UTC)

Finally, could "...The FSK signal requires constant transmitter power, which allows the use of Class C RF power amplification, while other modes require linear amplification..." be modified to "...The RTTY signal requires constant transmitter power, which allows the use of Class C RF power amplification, while other modes require linear amplification..."? Wa3frp (talk) 22:56, 19 March 2010 (UTC)

constant transmitter power is not required, but it is a feature, it could work with varying transmitter power, the important thing is that the power envelope is constant, so the signal can handle amplitude distortion, so C class is not a problem. So change the word requires to uses. Your comparison with PSK31, and spectral efficiency edit has no change, I suspect you wanted to edit it to something different!Graeme Bartlett (talk) 01:53, 20 March 2010 (UTC)

"Constant power" envelope of simple FSK (with discontinuous frequency steps) is a distinguishing feature. The wording can be improved.--Albany45 (talk) 18:43, 22 March 2010 (UTC)

I updated the section based on the above. I now realize that my use of "AFSK" above dates me. Originally, AFSK RTTY was AM-modulated VHF in the late 40's and into the 70s, I suspect. (FSK on VHF/UHF was practically impossible in the early days, because equipment was not very stable.) In the current literature AM AFSK is hardly mentioned, and "AFSK" means using AF tones from a soundcard to modulate an SSB transmitter. Much ink is spilled (see above!) on whether that kind of "AFSK" is the same as directly generated FSK (i.e. FM modulating an RF or IF oscillator with the data waveform). Mathematically, they are identical, except that the AFSK method allows for noise and distortion to be added to the transmitted signal if the sound card and the transmitter connection are not set up right. Should these points be made in the technical description section?--Albany45 (talk) 17:33, 23 March 2010 (UTC)

Technical description too technical

I understand that this section is a technical description, but even for a technical description it is too technical. There is an excessive amount of unexplained jargon, with acronyms or terms like "UART," "mark state," "digital logic levels," and "5-bit character." I'm a layperson and extremely, hopelessly lost. Please, someone rewrite this section in friendlier, streamlined terms. It might help to break it into subsections under the main heading. Could the three distinct parts be their own subsections? i.e. Teletype, Modem, and Radio — Preceding unsigned comment added by Contortrix (talk • contribs) 20:27, 17 July 2012 (UTC)

HI Amy, I'm not sure if you are still active on Wikipedia as I see that your last edit was done on July 2012, but I thought that I'd reply anyway. You noted above that acronyms or terms like "UART," "mark state," "digital logic levels," and "5-bit character" appear to be unexplained jargon. I've just checked and the terms, such as UART and digital logic, link to the main article on that subject. I've added a link for five-bit character. I hope that this helps you. Wa3frp (talk) 15:34, 25 August 2012 (UTC)