National HRO
A shortwave receiver with micrometer dial and plug-in coils.
The National HRO was a nine-tube shortwave communications receiver built by the National Radio Company in Malden, Massachusetts. Its mechanical design was overseen by James Millen (call sign W1HRX). The electronics were reportedly designed in Pasadena, California, in the garage of Herbert Hoover, Jr. (W6ZH), son of the U.S. president, along with Howard Morgan of Western Electric. Dana Bacon (W1BZR) also contributed and co-wrote about the receiver with Millen. The name originated from overtime slips marked "HOR" for "Hell Of a Rush" by National’s toolmakers; management softened it to "HRO" to make it less objectionable, though it was quickly said to stand for "Helluva Rush Order."
Announced in QST magazine in October 1934 and shipped in March 1935, the HRO incorporated features requested by the emerging airline industry that also appealed to amateur radio operators. According to the 1935 manual, the receiver cost US$233, the external power supply (which reduced heat and hum) was US$26.50 without tubes, and a 7000-ohm speaker in a rack panel was US$30.00.
During World War II, the HRO became the preferred receiver for Allied monitoring services, including Y-Service stations linked to the codebreakers at Bletchley Park (Station X) in England. Britain initially bought about 1,000 standard HROs, and roughly 10,000 total were used by the British for intercept operations, diplomatic communications, aboard ships, at shore stations, and for clandestine work.
The receiver’s two most distinctive features were a micrometer-type dial and plug-in tuning coil sets that slid into a full-width opening at the bottom of the front panel. The dial, designed by William Graydon Smith, allowed continuous analog tuning while digitally showing incremental progress over ten full turns of the large tuning knob. Ten times the dial’s circumference measured 12 feet (nearly 4 meters), providing fine frequency resolution. The four standard coil sets—A, B, C, and D—covered 14–30, 7–14.4, 3.5–7.3, and 1.7–4 MHz, respectively. Two optional sets, E and F, covered 960–2050 kHz and 480–960 kHz. Before leaving the factory, a technician spent nearly four hours custom-calibrating a set of A, B, C, and D coils for each radio. Each main coil set also had bandspread modes, set by moving screws, that limited the frequency range to 28–29.7, 14–14.4, 7–7.3, and 3.5–4 MHz for amateur use.
- Manufacturer
- National Radio Company
- Location
- Malden, Massachusetts, United States
- Type
- 9-tube HF general coverage communications receiver
- Announced
- October 1934 in QST magazine
- First shipped
- March 1935
- Original price (1935)
- US$233
- External power supply price (1935)
- US$26.50 less tubes
Lore & Background
The mechanical design was overseen by James Millen (amateur call sign W1HRX) in Massachusetts. According to several accounts, Herbert Hoover, Jr. (W6ZH), son of U.S. President Herbert Hoover, and Howard Morgan of Western Electric designed the electronics in Hoover's garage in Pasadena, California. Dana Bacon (W1BZR) was also involved and co-authored a piece on the receiver with Millen. The name HRO originated from overtime slips marked HOR for 'Hell Of a Rush' by tool makers; management chose the slight alteration HRO to make it less objectionable, though it was quickly said to stand for 'Helluva Rush Order'.
The two most distinctive features were a micrometer-type dial designed by Willam Graydon Smith, which allowed continuous analog tuning with digital indication over ten full turns of the large knob, and plug-in sets of tuning coils that slid into a full-width opening at the bottom of the front panel. Four standard coil sets (A, B, C, D) covered 14–30, 7–14.4, 3.5–7.3, and 1.7–4 MHz respectively; two optional sets (E and F) covered 960–2050 kHz and 480–960 kHz. Each radio left the factory with a set of A, B, C, and D coils custom calibrated by a technician in a process taking nearly four hours. The four main coil sets also had bandspread modes for amateur bands.
Reader's Guide
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 operations, diplomatic communications, aboard ships, at shore stations, and for clandestine use. The U.S. military told National to 'Start building HROs. We'll tell you when to stop.' Before, during, and after World War II, the HRO concept of plug-in coils with micrometer tuning was copied in several countries, including Germany and Japan; the best-known copies are the German KST by Korting Radio and the R4 by Siemens. Postwar models included the HRO-7, HRO-50, HRO-50-1, and HRO-60, followed by two solid-state receivers that did not use plug-in coils: the HRO-500 and HRO-600. The HRO-600 broke tradition by using a frequency counter instead of a micrometer tuning dial, and ironically used nixie tubes for its digital display, making it no longer all solid-state. HRO receivers continued to be popular even after better and more expensive general coverage receivers from companies such as Collins Radio became available in the 1950s and later. Restored examples dating back to the original model are still found among vintage amateur radio enthusiasts.
Did You Know?
- The micrometer dial allowed continuous tuning over ten full turns, giving a tuning circumference of 12 feet.
- An estimated 10,000 HROs were used by the British during World War II.
- The HRO-600 used nixie tubes for its digital frequency display, making it not all solid-state.
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