Radiofacsimile,radiofax orHF fax is ananalogue mode for transmittinggrayscale images viahigh frequency (HF)radio waves. It was the predecessor toslow-scan television (SSTV). It was the primary method of sending photographs from remote sites (especially islands) from the 1930s to the early 1970s. It is still in limited use for transmitting weather charts and information to ships at sea.
.jpg)
.jpg)
Richard H. Ranger, anelectrical engineer working atRadio Corporation of America (RCA), invented a method for sending photographs through radio transmissions. He called his system the wireless photoradiogram, in contrast to the fifty-year-oldtelefacsimile devices which used firsttelegraphic wires, and then later was adapted to use the newertelephone wires.
On 29 November 1924, Ranger's system was used to send a photograph from New York City to London. It was an image of PresidentCalvin Coolidge and was the first transoceanic radio transmission of a photograph. Also that year,AT&T engineerHerbert E. Ives transmitted the first color photograph.[2]
Charles J. Young, son of the RCA founderOwen D. Young, andErnst Alexanderson, developed a radio facsimile system forGeneral Electric. On 12 August 1931 this system successfully transmitted a copy of theUnion-Star newspaper ofSchenectady, New York to the transatlantic linersAmerica andMinnekahda. It took 15 minutes to copy a single page measuring8+1⁄2 by 9 inches (220 by 230 mm).[3]
Beginning in the late 1930s, the Finch Facsimile system was used to transmit a "radio newspaper" to private homes via commercial AM radio stations and ordinary radio receivers equipped with Finch's printer, which used thermal paper. Sensing a new and potentially golden opportunity, competitors soon entered the field, but the printer and special paper were expensive luxuries, AM radio transmission was very slow and vulnerable to static, and the newspaper was too small. After more than ten years of repeated attempts by Finch and others to establish such a service as a viable business, the public, apparently quite content with its cheaper and much more substantial home-delivered daily newspapers, and with conventional spoken radio bulletins to provide any "hot" news, still showed only a passing curiosity about the new medium.[4]
DuringWorld War II thousands of photographs were transmitted from Europe, and from the Pacific Islands, to the United States. The majornews agencies (AP,UPI,Reuters), maintained their own transoceanic radio facsimile transmitters as close to the action as they could. The iconicflag raising on Iwo Jima was printed in hundreds of American newspapers within a day of being taken, because it was transmitted fromGuam toNew York City by wireless radiofacsimile, a distance of 12,781 km (7,942 mi).[5][better source needed]
By the late 1940s, radiofax receivers were sufficiently miniaturized to be fitted beneath the dashboard ofWestern Union's "Telecar"telegram delivery vehicles.[6]
In the 1960s, theUnited States Army transmitted the first photograph via satellitefacsimile toPuerto Rico from theDeal Test Site using theCourier satellite.
A decade after the introduction of radiofaxNational Weather Service (NWS) began transmittingweather maps using the radiofax technology. The NWS named this new serviceweatherfax (portmanteau word from the words "weatherfacsimile") The cover of the regularNOAA publication on frequencies and schedules states "Worldwide Marine Radiofacsimile Broadcast Schedules".
Facsimile machines were used in the 1950s to transmitweather charts across the United States via land-lines first and then internationally viaHF radio. Radio transmission of weather charts provides an enormous amount of flexibility tomarine andaviation users for they now have the latest weather information andforecasts at their fingertips to use in the planning of voyages.
Radiofax relies on facsimile technology where printed information is scanned line by line and encoded into an electrical signal which can then be transmitted via physical line or radio waves to remote locations. Since the amount of information transmitted per unit time is directly proportional to thebandwidth available, then the speed at which a weather chart can be transmitted will vary depending on the quality of the media used for transmission.
Today radiofax data is available viaFTP downloads from sites in theInternet such as the ones hosted by the National Oceanic and Atmospheric Administration (NOAA). Radiofax transmissions are also broadcast by NOAA from multiple sites in the country at regular daily schedules. Radio weatherfax transmissions are particularly useful to shipping, where there are limited facilities for accessing the Internet.
The term weatherfax was coined after the technology that allows the transmission and reception of weather charts (surface analysis, forecasts, and others) from a transmission site (usually the meteorological office) to a remote site (where the actual users are).
Radiofax may also be used to transmit pages ofnewspapers. Stations like JJC use this way of transmitting news by using radio facsimile technology.
Radiofax is transmitted insingle sideband which is a refinement ofamplitude modulation. The signal shifts up or down a given amount to designate white or black pixels. Adeviation less than that for a white or black pixel is taken to be a shade of grey. With correct tuning (1.9 kHz below the assigned frequency for USB, above for LSB), the signal shares some characteristics withSSTV, with black at 1.5 kHz and peak white at 2.3 kHz.
Usually, 120 lines per minute (LPM) are sent (For monochrome fax, possible values are: 60, 90, 100, 120, 180, 240. For colour fax, LPM can be: 120, 240[7]). A value known as theindex of cooperation (IOC) must also be known to decode a radio fax transmission - this governs the image resolution, and derives from early radio fax machines which used drum readers, and is the product of the total line length and the number of lines per unit length (known sometimes as thefactor of cooperation), divided byπ. Usually the IOC is 576.
APT format permits unattended monitoring of services. It is employed by most terrestrial weather facsimile stations as well as geostationary weather satellites.
| Signal | Duration | IOC576 | IOC288 | Remarks |
|---|---|---|---|---|
| Start tone | 5s | 300 Hz | 675 Hz | 200 Hz for colour fax modes. |
| Phasing signal | 30s | Black line interrupted by a white pulse. | ||
| Image | Variable | 1200 lines | 600 lines | At 120 lpm. |
| Stop tone | 5s | 450 Hz | 450 Hz | |
| Black | 10s |
Today, radiofax is primarily used worldwide for the dissemination of weather charts,satellite weather images, and forecasts to ships at sea. The oceans are covered by coastal stations in various countries.
In the United States, fax weather products are prepared by a number of offices, branches, and agencies within theNational Weather Service (NWS) of theNational Oceanic and Atmospheric Administration (NOAA).
Tropical and hurricane products come from theTropical Analysis and Forecast Branch, part of theTropical Prediction Center/National Hurricane Center. They are broadcast over US Coast Guard communication stationsNMG, inNew Orleans, LA, and NMC, the Pacific master station on Point Reyes, California. AfterHurricane Katrina damaged NMG, the Boston Coast Guard station NMF added a limited schedule of tropical warning charts. NMG is back at full capability, but NMF continues to broadcast these.
All other products come from theOcean Prediction Center (OPC) of the NWS, in cooperation with several other offices depending on the region and nature of information. These also use NMG, NMC, and NMF, plus Coast Guard station NOJ inKodiak, Alaska, and Department of Defense station KVM70 inHawaii.
Ever since the loss of theRMSTitanic highlighted the dangers oficebergs in the North Atlantic, anInternational Ice Patrol has also originated weather data, and its charts are broadcast by the Boston station during the prime iceberg season of February through September, using the call sign NIK.
CBV, Playa Ancha Radio inValparaiso,Chile broadcasts a daily schedule of Armada de Chile weather fax for the southeastern Pacific, all the way to the Antarctic. Also in the Pacific,Japan has two stations, as does the Bureau of Meteorology inAustralia. Most European countries have stations, as doesRussia.
Kyodo News is the only remaining news agency to transmit news via radiofax. It broadcasts complete newspapers in Japanese and English, often at 60 lines per minute instead of the more normal 120 because of the greater complexity of written Japanese. A full day's news takes dozens of minutes to transmit. Kyodo has a dedicated transmission to Pacific fishing fleets from Kagoshima Prefectural Fishery Radio, and a relay from 9VF/252, which is said to be located inSingapore. These transmitters are considerably more powerful than others used for this mode.
The German Meteorological Service (Deutscher Wetterdienst, DWD) transmits a regular daily schedule of weather charts on three frequencies 3.855 MHz, 7.88 MHz and 13.8825 MHz from their LF and HF transmitting facility inPinneberg.
