National HRO
Encyclopedia
The original National HRO was a 9-tube shortwave
general coverage communications receiver
manufactured by the National Radio Company
of Malden, Massachusetts
, USA.
, and Howard Morgan (of Western Electric
) designed the electronics in Hoover's garage in Pasadena, California
. 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".
The HRO receiver was first announced in QST
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, 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
speaker in a rack panel was US$30.00. The HRO found widespread use during World War II
as the preferred receiver of various Allied monitoring services, including Y-Service stations associated with the code-breaking group at Bletchley Park
(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.
-type dial, and plug-in tuning coils that slid into a full-width opening at the bottom of the front panel. The dial, designed by James Millen, allowed for 500 tuning steps 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 coils, A, B, C, and D, covered 14-30, 7-14.4, 3.5-7.3, and 1.7-4 MHz, respectively. Two other 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. Each of the four main coils also had bandspread 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.
There were also several sub-variations on these models.
, 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 WWII
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 tubes 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 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
enthusiasts and other hobbyists.
Shortwave
Shortwave radio refers to the upper MF and all of the HF portion of the radio spectrum, between 1,800–30,000 kHz. Shortwave radio received its name because the wavelengths in this band are shorter than 200 m which marked the original upper limit of the medium frequency band first used...
general coverage communications receiver
Communications receiver
A communications receiver is a type of radio receiver used as a component of a radio communication link.-Features:Commercial communications receivers are characterised by high stability and reliability of performance, and are generally adapted for remote control and monitoring...
manufactured by the National Radio Company
National Radio Company
The National Radio Company, headquartered in Malden, Massachusetts, USA was an American manufacturer of radio equipment from 1914 to 1991.-History:...
of Malden, Massachusetts
Massachusetts
The Commonwealth of Massachusetts is a state in the New England region of the northeastern United States of America. It is bordered by Rhode Island and Connecticut to the south, New York to the west, and Vermont and New Hampshire to the north; at its east lies the Atlantic Ocean. As of the 2010...
, USA.
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 HooverHerbert Hoover
Herbert Clark Hoover was the 31st President of the United States . Hoover was originally a professional mining engineer and author. As the United States Secretary of Commerce in the 1920s under Presidents Warren Harding and Calvin Coolidge, he promoted partnerships between government and business...
, and Howard Morgan (of Western Electric
Western Electric
Western Electric Company was an American electrical engineering company, the manufacturing arm of AT&T from 1881 to 1995. It was the scene of a number of technological innovations and also some seminal developments in industrial management...
) designed the electronics in Hoover's garage in Pasadena, California
Pasadena, California
Pasadena is a city in Los Angeles County, California, United States. Although famous for hosting the annual Rose Bowl football game and Tournament of Roses Parade, Pasadena is the home to many scientific and cultural institutions, including the California Institute of Technology , the Jet...
. 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".
The HRO receiver was first announced in QST
QST
QST is a magazine for amateur radio enthusiasts, published by the American Radio Relay League . It is a membership journal that is included in membership with the ARRL. The publisher claims that circulation of QST in the United States is higher than all amateur radio-related publications in the...
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, 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
The ohm is the SI unit of electrical resistance, named after German physicist Georg Simon Ohm.- Definition :The ohm is defined as a resistance between two points of a conductor when a constant potential difference of 1 volt, applied to these points, produces in the conductor a current of 1 ampere,...
speaker in a rack panel was US$30.00. The HRO found widespread use during World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
as the preferred receiver of various Allied monitoring services, including Y-Service stations associated with the code-breaking group at Bletchley Park
Bletchley Park
Bletchley Park is an estate located in the town of Bletchley, in Buckinghamshire, England, which currently houses the National Museum of Computing...
(Station X) in England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
. 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 micrometerMicrometer
A micrometer , sometimes known as a micrometer screw gauge, is a device incorporating a calibrated screw used widely for precise measurement of small distances in mechanical engineering and machining as well as most mechanical trades, along with other metrological instruments such as dial, vernier,...
-type dial, and plug-in tuning coils that slid into a full-width opening at the bottom of the front panel. The dial, designed by James Millen, allowed for 500 tuning steps 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 coils, A, B, C, and D, covered 14-30, 7-14.4, 3.5-7.3, and 1.7-4 MHz, respectively. Two other 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. Each of the four main coils also had bandspread 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 ParkBletchley ParkBletchley Park is an estate located in the town of Bletchley, in Buckinghamshire, England, which currently houses the National Museum of Computing...
) - HRO-5 (1944–1945, octal tube version).
There were also several sub-variations on these models.
Production
The US military told National, "Start building HROs. We'll tell you when to stop.". Before, during, and after WWIIWorld War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
, the HRO concept of using plug-in coils with micrometer tuning was copied in several countries, including Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
and Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
. 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 WWII
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
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 tubes 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 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
Vintage amateur radio is a subset of the amateur radio hobby, considered a form of nostalgia much like antique car collecting, where enthusiasts collect, restore, preserve, build, and operate amateur radio equipment from bygone years, most notably those using vacuum tube technology.Popular modes of...
enthusiasts and other hobbyists.
See also
- ARC-5ARC-5The AN/ARC-5 Command Radio Set is a series of radio receivers, transmitters, and accessories used to provide two-way Morse code and AM radiotelephone communication for U.S. Navy aircraft during World War II and the years following. It was an improvement of the Navy's ARA/ATA command set. Similar...
- ART 13 transmitter
- BC-348BC-348The 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:...
- BC-654BC-654The 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-654 and associated support equipment.The BC-654 first saw...
- Collins Radio
- Hammarlund super proHammarlund Super ProThe Hammarlund Super Pro was an American made radio communications receiver.- History :In March 1936, the Hammarlund Manufacturing Company initiated the first of the famous “Super-Pro” line, the SP-10 receiver, followed in January 1937 by the SP-100...
- R-390AR-390AThe R-390A /URR is a general coverage HF radio communications receiver designed by Collins Radio Company for the US military.-History:The R-390A military shortwave radio receiver was the result of a project undertaken by the U. S. Army Signal Corps in 1954 to replace the existing R-390 receiver...
- Vintage amateur radioVintage amateur radioVintage amateur radio is a subset of the amateur radio hobby, considered a form of nostalgia much like antique car collecting, where enthusiasts collect, restore, preserve, build, and operate amateur radio equipment from bygone years, most notably those using vacuum tube technology.Popular modes of...
External links
- The Evolution of the National HRO and Its Contribution to Winning World War II
- HRO receiver
- HRO receiver models
- National Radio product line
- A brief history of the National Company, Inc.
- National Radio with HRO details
- Downloadable copies of HRO manuals
- Radio Museum with searchable data base
- Dating The Early HRO, Antique Wireless Association