Radioteletype Communication Methods and Evolution

Radioteletype communication has a rich history, with various methods emerging over the years. The first radioteletype system was developed in the 1920s.

In the early days, radioteletype communication relied on Morse code, which was a time-consuming and labor-intensive process. It wasn't until the 1930s that the first teletype machines were introduced, allowing for faster communication.

These early teletype machines used a mechanical printer to produce typed pages, which were then transmitted over the airwaves. The machines were bulky and required a lot of maintenance, but they paved the way for more advanced systems.

The history of RTTY is a fascinating story that spans over a century. Landline teleprinter operations began in 1849 with a circuit between Philadelphia and New York City.

Émile Baudot designed a five-unit code in 1874 that is still in use today, marking a significant milestone in the evolution of RTTY. Teleprinter system design continued to improve, and by the beginning of World War II, it became the principal distribution method used by news services.

The US Department of the Navy successfully tested printing telegraphy between an airplane and ground radio station in August 1922, paving the way for the development of radioteletype.

The early history of amateur RTTY is a fascinating story. The first amateur radio operators, known as "hams", began experimenting with RTTY in the 1920s.

In the 1920s, amateur radio operators in the United States and Europe started using RTTY for communication. They were attracted to the technology's potential for efficient and reliable communication.

The first RTTY equipment was built by amateur radio operators themselves, using homemade kits and scavenged parts. This pioneering spirit laid the foundation for the development of modern RTTY technology.

RTTY became a popular mode of communication among amateur radio operators in the 1930s, with many operators using it for contesting and DXing.

The Baudot code, used in RTTY, was designed by Émile Baudot in 1874 and is still in use today. It's a five unit code that was a significant improvement over earlier systems.

The Baudot code was chosen for its simplicity, which allowed for faster transmission speeds. However, this simplicity came at a cost: the code does not use any error correction, which made it more prone to errors in radio transmission.

Consider reading: Did the Telegraph Used Morse Code

Radio transmission, especially on short wave, is quite different from wireline transmission. A short crack in the signal can cause a bit to be falsified, making reliable data transmission more difficult.

The operator's influence was crucial in determining the success of a QSO, or contact, with RTTY. An experienced operator could save a QSO by recognizing typical misspellings and knowing how contest participants behaved.

The lack of error correction in the Baudot code was a compromise made to increase speed, but it's a challenge that RTTY operators still face today.

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Tape and Relay Centers played a crucial role in the development of RTTY technology. The three types of centers were Torn Tape Centers, Semi-Automatic Centers, and Automatic Centers.

Torn Tape Centers were a common sight in early RTTY operations. They used a variety of receiving converters, including the FRB and CV-97/UX models.

In Semi-Automatic Centers, operators relied on keying machines like the MD-168/UX and KY-44A/FX to transmit messages. These machines were essential for sending coded messages over RTTY channels.

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Automatic Centers, on the other hand, used fax recorders like the RD-92/UX and AN/UXH-2 to transmit messages without the need for manual keying. The TT-41/TXC-1B and TT-66/TXC fax scanner and recorders were also used in these centers.

Here are some examples of the equipment used in these centers:

The original radioteletype system is based on the Baudot code or ITA-2 5-bit alphabet. This system uses character asynchronous transmission with 1 start bit and 1, 1.5, or 2 stop bits.

Transmitter modulation is normally Frequency Shift Keying (FSK), although occasionally an AFSK signal modulating an RF carrier is used on VHF or UHF frequencies. The standard transmission speeds are 45.45, 50, 75, 100, 150, and 300 baud.

Common carrier shifts are 85 Hz, 170 Hz, 425 Hz, 450 Hz, and 850 Hz, although some stations use non-standard shifts. RTTY transmissions on LF and VLF frequencies use a narrow shift of 85 Hz due to the limited bandwidth of the antennas.

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Some combinations of speed and shift are standardized for specific services: amateur radio transmissions are almost always 45.45 baud – 170 Hz, and NATO military services use 75 or 100 baud – 850 Hz.

The technical parameters of a 2FSK transmission are determined by two parameters: the distance between the two tones and the scanning speed. In amateur radio, the distance ('shift') is fixed at 170 Hz, and the scanning speed at 45 baud (exactly 45.45 Bd).

The 5-bit Baudot data must be converted into the 8-bit ASCII (or UTF-8) data used by modern computers for decoding. This was also done by a converter in the past, the data was then output via a classic RS-232 serial interface.

Here are the standardized combinations of speed and shift for specific services:

RTTY data transmission is surprisingly slow, with a writing speed of around 6 characters/second in the early days and 13 characters/second later on.

The use of electromechanical teleprinters, like those used in the telex system, was a marvel of precision engineering.

Operating without error correction was still viable for wireline transmission, but radio transmission on short wave is quite different, with a short crack enough to falsify a bit.

The serial data code used in RTTY, called Baudot code, uses 5 bits per character, resulting in a maximum of 32 possible codes, which is just enough to represent the alphabet and a few special characters.

A change of levels in RTTY data transmission can be disastrous if lost during the transfer, resulting in characters being printed in the last selected level.

The lack of error correction in RTTY makes reliable data transmission more difficult, especially on short wave, where a short crack can falsify a bit.

RTTY's simplicity is also its strength, with a high tone for a logical one and a low tone for a logical zero, making it easily created with amateur means.

The challenge of RTTY lies in its weaknesses, which require skilful operation and experience to master, making it a more engaging and rewarding mode to use.

Expand your knowledge: Joint Data Network

RTTY has a typical baud rate for Amateur operation of 45.45 baud, which translates to approximately 60 words per minute.

This relatively slow transmission speed means RTTY has low spectral efficiency, requiring around 250Hz receiver bandwidth, more than double that required by PSK31.

In theory, the shift size can be decreased to 22.725Hz, reducing the overall band footprint substantially.

RTTY, using either AFSK or FSK modulation, produces a waveform with constant power, allowing for the use of a more efficient Class C amplifier.

This is in contrast to many digital transmission modes, which require linear amplifiers.

Despite its weaknesses, RTTY remains popular as a "keyboard to keyboard" mode in Amateur Radio.

Modern digital modes, such as MFSK, offer much better data reliability through the use of Forward Error Correction.

However, RTTY has its own unique challenge, which can only be mastered with experience and a little dedication.

This challenge is part of its appeal, making RTTY a more engaging mode for operators.

Worth a look: Digital Private Mobile Radio

Radioteletype operators can benefit from a variety of equipment manuals and descriptions.

Robert Downs WA5CAB has shared his manuals, which are a great resource for those looking to learn more about various units of equipment. His information is a valuable contribution to the community.

Manuals for specific devices like the CV-116/URR FSK converter and the TMC SFO, SFO-1, SFO-2 teletype regenerator are also available.

The 1953 Directory of military communication equipment is a comprehensive resource that provides an overview of the communication equipment used during that time period.

Here are some specific manuals and resources mentioned in the article:

Military Surplus Units 1972 were listed in a 1.0 MB pdf document that's available for download. It includes brief descriptions of the units.

The pdf document is a valuable resource for those interested in military surplus RTTY units from 1972. It's a great starting point for anyone looking to learn more about these units.

The document can be found online, making it easily accessible to anyone with an internet connection.

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Communication equipment manuals and descriptions are a treasure trove of information for those looking to understand and work with various communication systems.

Robert Downs WA5CAB has shared his manuals, which are a valuable resource for anyone interested in communication equipment.

Manuals for the CV-116/URR FSK converter and TMC SFO, SFO-1, SFO-2 teletype regenerator are also available, offering detailed descriptions of these units.

The 1953 Directory of military communication equipment is a comprehensive resource that provides an overview of the various equipment used during that time.

For those looking for specific information, here are some key manuals and resources to consider:

Keyers - FSK/AFSK Converters are used to convert audio signals into digital data for transmission.

Robert Downs WA5CAB has shared manuals and information on various units, including keyers.

FSK (Frequency Shift Keying) is a transmission method where the signal shifts between two frequencies, and it's still used today.

Early FSK keyers include the FSA, FSB, and FSC models.

For FSK transmission, the distance between the two tones is fixed at 170 Hz, and the scanning speed is 45 baud (exactly 45.45 Bd).

The KY-30/GRT is an example of an FSK keyer.

The TH-39/UGT and TH-39A/UGT are AFSK (Amplitude Shift Keying) keyers, specifically the TMC TIS-2 and TIS-3 models.

Here are some examples of keyers and FSK/AFSK converters: