The first ARQ-M link was built in the Netherlands, and began exchanging messages with a counterpart in New York in 1947.
In contrast, radio communications are subject to a wide variety of noises and other signal problems that leads to losses.
To forward telex messages successfully over radio links, some form of error correction should be applied.
[1][5] By 1956 ARQ radio circuits were running from New York to Amsterdam, Berne, Brussels, Frankfurt, London, Paramaribo, Paris, Rome, and Wien, with plans for Copenhagen, Lisbon, Madrid, and Oslo.
[1] International shortwave ARQ data links have been replaced by undersea cables and satellite circuits.
[5] The New Zealand Post Office used a two channel multiplex ARQ system to communicate on two circuits between Wellington and Vancouver and Sydney over shortwave radio for a few years till 1961.
[10] The Department of Transport in Australia used to run several multiplexed ARQ data links to remote airports prior to the use of AUSSAT.
[11] A station at Perth, VZPH and VKP communicated with Cocos Island VZCC, Port Hedland VZPD, Darwin VZPM, and Sydney VZSY.
[11] The stations in Sydney (Pernrith Rx, Llandilo Tx) communicated with Alice Springs, VZAS, Mount Isa, VZMA, Norfolk Island VZNF, and Lord Howe Island, VZLH.
One link ran between Companhia Portuguesa Radio Marconi in Lisbon and the Vatican.
Canadian armed forces used shortwave radio as satellite links into the Arctic are difficult.
[15] In order to synchronise to the synchronous data stream the encoded characters can be sent erect or inverted.
These rates allowed running at the same speed as 50 baud Telex landline systems.
If the raw error rate increases to 3% the link will be blocked all the time with retransmissions.
[25] In practice use of subchannels has not been observed although international partial rate fixed services were once available.
ARQ-M was standardised by the Comité consultatif international pour la radio.
The XII Plenary session in New Delhi in 1970 approved recommendation 342-2 Automatic error-correcting system for telegraph signals transmitted over radio circuits.
[16] The CCITT produced recommendation S.13 [26] Use on radio circuits of 7-unit synchronous systems giving error correction by automatic repetition.
[29][30] Companies that manufactured equipment for this system were found in Germany, Japan, Netherlands, Switzerland, and USA.
Hasler from Berne in Switzerland made a four channel TOR (Telex on Radio) system.
The channel divider has output control lines for each subchannel A1 A2 A3 A4 B1 ... for both receive and transmit sides.
Each subchannel on the send section side includes a serial to parallel converter, and a tripping pulse that clocks in the next character.
[5] On the send section the channel circuit includes a delay line feeding a repetition storage.
From here the five bit code goes to a parallel to serial converter, controlled by a repetition cycle timer on the receive side.
[5] Because the telex network does not give feedback to a sender about when a message is delivered, and a shortwave ARQ link may or may not be available, systems with ARQ links set them up to be store and forward half duplex systems.
Call charges were calculated for the time when the link was running without errors, either at six or ten second increments.
Two stations communicating with ARQ-M will use two different frequencies as data is continuously transmitted in each direction.
Channels are often running in idle mode and have a rhythmic sound, as the symbol pattern repeats every 7/12 second.
Such a chart will show 24 pulses on each line for a two channel system, forming columns down the page.
[15] Software is available to receive and decode utility transmissions that use ARQ-M including Go2MONITOR,[37][38][39] and there is also hardware such as the Code300-A from Hoka Electronic,[40] and Wavecom M 4010.