National HRO
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The original National HRO was a 9-tube HF (
shortwave Shortwave radio is radio transmission using shortwave (SW) radio frequencies. There is no official definition of the band, but the range always includes all of the high frequency band (HF), which extends from 3 to 30 MHz (100 to 10 me ...
) general coverage
communications receiver A communications receiver is a type of radio receiver used as a component of a radio communication link. This is in contrast to a ''broadcast receiver'' which is used to receive radio broadcasts. A communication receiver receives parts of the r ...
manufactured by the
National Radio Company The National Radio Company, headquartered in Malden, Massachusetts, United States, was an American manufacturer of radio equipment from 1914 to 1991. History The company was incorporated, in 1914, as the "National Toy Company", but by 1916 had inc ...
of Malden,
Massachusetts Massachusetts (Massachusett language, Massachusett: ''Muhsachuweesut assachusett writing systems, məhswatʃəwiːsət'' English: , ), officially the Commonwealth of Massachusetts, is the most populous U.S. state, state in the New England ...
, United States.


History

James Millen (amateur radio call sign W1HRX) in Massachusetts was in charge of the mechanical design. According to several accounts, Herbert Hoover, Jr. (amateur radio call sign W6ZH), son of US President Herbert Hoover, and Howard Morgan (of
Western Electric The Western Electric Company was an American electrical engineering and manufacturing company officially founded in 1869. A wholly owned subsidiary of American Telephone & Telegraph for most of its lifespan, it served as the primary equipment ma ...
) designed the electronics in Hoover's garage in
Pasadena, California Pasadena ( ) is a city in Los Angeles County, California, northeast of downtown Los Angeles. It is the most populous city and the primary cultural center of the San Gabriel Valley. Old Pasadena is the city's original commercial district. I ...
. Dana Bacon (W1BZR) was also involved and wrote about the receiver as second author with James Millen. Some of National Radio's tool makers marked their overtime slips with HOR for "Hell Of a Rush." Management decided that a version of that abbreviation should be the name of the new receiver, choosing the slight alteration HRO to make it less objectionable. That was quickly countered by saying that HRO stood for "Helluva Rush Order".http://www.qsl.net/jms/bio_rem/bhnc.html Antique Wireless Association The HRO receiver was announced in
QST ''QST'' is a magazine for amateur radio enthusiasts, published by the American Radio Relay League (ARRL). It is a membership journal that is included with membership in the ARRL. The publisher claims that circulation of ''QST'' in the United St ...
magazine in October 1934 and shipped in March 1935, incorporating many design features requested by the fledgling airline industry that were also attractive to the amateur radio community. According to the 1935 instruction manual,ftp://bama.sbc.edu/downloads/national/hro1935/ National HRO Manual the HRO price was US$233, the external power supply (to reduce heat in the receiver cabinet and hum) was US$26.50 less tubes, and a 7000
ohm Ohm (symbol Ω) is a unit of electrical resistance named after Georg Ohm. Ohm or OHM may also refer to: People * Georg Ohm (1789–1854), German physicist and namesake of the term ''ohm'' * Germán Ohm (born 1936), Mexican boxer * Jörg Ohm (b ...
speaker in a rack panel was US$30.00. The HRO found widespread use during
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
as the preferred receiver of various Allied monitoring services, including Y-Service stations associated with the code-breaking group at
Bletchley Park Bletchley Park is an English country house and estate in Bletchley, Milton Keynes ( Buckinghamshire) that became the principal centre of Allied code-breaking during the Second World War. The mansion was constructed during the years following ...
(Station X) in England. An estimated 1,000 standard HROs were initially purchased by Great Britain, and approximately 10,000 total saw use by the British in intercept operation, diplomatic communications, aboard ships and at shore stations as well as for clandestine use.


Features

The two most distinctive features of this radio were its use of a
micrometer Micrometer can mean: * Micrometer (device), used for accurate measurements by means of a calibrated screw * American spelling of micrometre The micrometre ( international spelling as used by the International Bureau of Weights and Measures; ...
-type dial, and plug-in sets of tuning coils that slid into a full-width opening at the bottom of the front panel. The dial, designed by Willam Graydon Smith, allowed for continuous analog tuning while digitally indicating incremental progress over a range of ten full turns of the large tuning knob that tuned with velvet smoothness. Ten times the circumference of the dial is 12 feet (nearly 4 m), which allowed for great frequency resolution. The four standard sets of coils, A, B, C, and D, covered 14-30, 7-14.4, 3.5-7.3, and 1.7-4 MHz, respectively. Two other sets of coils, E and F, sold separately, covered 960–2050 kHz and 480–960 kHz, respectively. Before each radio left the factory, a technician custom calibrated a set of A, B, C, and D coils for that particular radio, a process that took nearly 4 hours.http://www.qsl.net/jms/bio_rem/bhnc.html National Receivers Each of the four main sets of coils also had
bandspread In a radio receiver, a bandspread control is a secondary tuning control that allows accurate tuning of closely spaced frequencies of a radio band. With a main tuning control that covered a wide range of frequencies, for example 10-14 megahertz in a ...
modes set by moving screws that limited the frequency range to 28-29.7, 14-14.4, 7-7.3, 3.5-4 MHz, respectively, for amateur radio use.


Models

Main HRO models: *HRO (also called HRO-Sr, 1935–1943) *HRO-Jr (February 1936 – 1943, US$100 version of Sr with only one coil not individually aligned to the receiver and lacking crystal filter, phasing control, and signal strength meter) *RAS (1939-?, HRO-Jr for US Navy with general coverage coils and 175 kHz IF so the radio could receive the 500 kHz distress frequency) *HRO-M (used in conjunction with
Bletchley Park Bletchley Park is an English country house and estate in Bletchley, Milton Keynes ( Buckinghamshire) that became the principal centre of Allied code-breaking during the Second World War. The mansion was constructed during the years following ...
) *HRO-5 (1944–1945, octal tube version) There were also several sub-variations on these models.


Production

The
US military The United States Armed Forces are the Military, military forces of the United States. The armed forces consists of six Military branch, service branches: the United States Army, Army, United States Marine Corps, Marine Corps, United States N ...
told National, "Start building HROs. We'll tell you when to stop." Before, during, and after
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
, the HRO concept of using plug-in coils with micrometer tuning was copied in several countries, including Germany and Japan. The best known copies are probably two German models widely employed as monitoring receivers by the German services, the KST made by Korting Radio and the R4 made by Siemens. Following World War II came the HRO-7 (1947–1949, 12 tubes, including 2 miniature tubes), HRO-50 (1949–1950, built-in tuning dials and power supply, push-pull audio amplifier, improved styling and performance), HRO-50-1 (1951, increased IF selectivity), and HRO-60 (1952–1964, dual conversion for coils B (7-14.4 MHz) and A (14-30 MHz), heater current regulation for the HF oscillator and mixer tubes). These were followed by two solid-state receivers that did not use plug-in coils: the HRO-500 (October 1964 – 1972, 5 kHz - 30 MHz, and HRO-600 (1970-1972?, 16 kHz - 30 MHz). Breaking with tradition, the HRO-600 used a frequency counter instead of a micrometer tuning dial. Ironically, the HRO-600 used
nixie tube A Nixie tube ( ), or cold cathode display, is an electronic device used for displaying numerals or other information using glow discharge. The glass tube contains a wire-mesh anode and multiple cathodes, shaped like numerals or other symbo ...
s for its digital frequency display and thus was, technically, no longer "all solid-state" as its predecessor, the HRO-500, had been. HRO receivers were said to be outstanding and continued to be popular although even better and more expensive general coverage receivers from such companies as
Collins Radio Rockwell Collins was a multinational corporation headquartered in Cedar Rapids, Iowa, providing avionics and information technology systems and services to government agencies and aircraft manufacturers. It was formed when the Collins Radio Compa ...
became available in the 1950s and later. One can still find HRO receivers dating back to the original model that have been restored by
vintage amateur radio Vintage amateur radio is a subset of amateur radio hobby where enthusiasts collect, restore, preserve, build, and operate amateur radio equipment from bygone years, such as those using vacuum tube technology. Popular modes of operation include spe ...
enthusiasts and other hobbyists.


See also

* ARC-5 *
ART 13 transmitter The AN/ART-13 was a radio transmitter manufactured by Collins Radio that found widespread use during and after World War II in military aircraft. History US Navy (T-47/ART-13 Radio Transmitter) training on board the USS Nereus, circa. 1952 In ...
*
BC-348 The BC-348 is a compact American-made communications receiver, which was mass-produced during World War II for the U.S. Army Air Force. Under the joint Army-Navy nomenclature system, the receiver system became known as the AN/ARR-11. History The ...
*
BC-654 The SCR-284 was a World War II era combination transmitter and receiver used in vehicles or fixed ground stations. History The Crosley Corporation of Cincinnati, Ohio manufactured the Signal Corps Radio set SCR-284 that consisted of the BC-6 ...
*
Hammarlund super pro The Hammarlund Super Pro was an American-made radio Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30  hertz (Hz) and 300  gigahertz (GHz). T ...
*
R-390A The R-390A /URR is a general coverage HF radio communications receiver designed by Collins Radio Company for the United States Armed Forces. History The R-390A military shortwave radio receiver was the result of a project undertaken by the United ...


References


External links


The Evolution of the National HRO and Its Contribution to Winning World War II








Originally published in
The AWA Review The Antique Wireless Association (AWA) is chartered as a non-profit educational organization in New York State and is an IRS 501(c)(3) tax-exempt corporation based in Bloomfield, New York. It was originally established in 1952 by Bruce Kelley, Geor ...
(Vol 1 1986)
National Radio with HRO details


{{DEFAULTSORT:National Hro Radiofrequency receivers Amateur radio receivers Military radio systems of the United States World War II American electronics Equipment of the United States Navy Military equipment introduced in the 1930s