by Harold A. Layer, KK6HY
update of article published in: "OTB," journal of the Antique Wireless Association, Vol. 34, No. 2, May 1993

Photo of Stoddart products

Photo of Stoddart NM40A in action on ship Photo of Stoddart NM40A in action on sub

Photo of NM-40A
NM-40A Receiver
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Photo of 533R-3
533R-3 Receiver
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Photo of NM40A NM-40A top
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Photo of NM-40A NM-40A bottom
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Photo of 533R-3 533R-3 top
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Photo of 533R-3 533R-3 bottom
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Radio historians have divided the development of radio receivers into several popular categories. Consoles, Deco, Wireless, Classics, Transistors, and Communications are examples of categories based on size, style, historical era, historical significance, circuit, or function, respectively.

I would like to propose another "function" category that has been neglected, yet vital to the history of radio communications: Research. This category would include those state-of-the-art, laboratory radio receivers designed for scientists and engineers in scientific studies of man-made, narrowband RF signals; naturally-occurring, broadband RF energy; communications surveillance and spectrum signature plotting; EMF field intensity and radio inteference; and antenna propagation surveys and measurements.

No company better represents this category than the Stoddart Aircraft Radio Company of Hollywood, California. It was founded by pioneer radio engineer, Richard R. Stoddart (born: 12/1/1900 - died: 9/26/1972). According to his official obituary he began his electronics career at age 15 by working for the Telefunken Wireless Company in New York, although another report indicates that he had a radio contract from Lee de Forest at age 14! After working as a radio operator on merchant ships, he also pursued another interest as a pilot, and barnstormed around the Poughkeepsie Airport during the 1920s. In the 1930s he was a field engineer for NBC. In 1938, Stoddart and Charles D. Perrine (W6CUH) designed the elaborate radio system for the historic Howard Hughes 1938 round-the-world flight. As the flight's radio officer,he was one of its five-man crew aboard the Lockheed two-engine plane and coordinated the complex communications links from country to country as the plane flew around the world in a record-breaking 91 hours, 8 minutes at an average speed of 218 miles-per-hour. The main radio room for this endeavor was on display at the New York World's Fair. In 1958, he was made a Fellow of the IEEE. The EMC Society now offers an annual "Stoddart Award" for technical excellence in the EMC field.

Hughes 1938 article, cover page
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Photo of 1938 Hughes article
Hughes 1938 article, page 2
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Photo of 1938 Hughes article
Hughes 1938 article, page 3
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In 1939 Stoddart worked for Lear Jet, but about a year later in 1940, he founded the Stoddart Aircraft Radio Company. In the beginning, it designed and manufactured VHF communication receivers and transmitters for airborne use, and these were important for the American support of England during World War II. Also, during the war, Stoddart produced its first research receiver, a VHF unit that featured both an average detector and a quasi-peak detector to measure narrowband and broadband radiation. In 1945, the company added the slide-back peak detector and precision signal calibration with a direct display of "microvolts-per-meter-per-kilocycle". Based on the value of this remarkable receiver to meet the growing sophistication of military communications research, the Navy contracted with Stoddart over the next decade to design and manufacture a group of receivers covering the entire RF spectrum from ELF to SHF (almost "DC to Daylight" as expressed during those years). Fig. 1 includes all models that I have been able to identify and date.

Closeup photo of NM40A dial
Closeup photo of Stoddart dial

NM-40A dial closeup

Before the advent of digital tuning, either a large analog dial or a multiple-band selector switch was required for careful tuning.

As a solution to accomodate the very narrow bandwidth window of the NM-40A, Stoddart built this gear-connected, spiral dial that allowed an incredible tuning width of 30 linear inches for its frequency range of 20 Hz to 15.5 kHz.

The 1956 NM-40A is a fascinating case-study of a Stoddart receiver and shares the fine design and craftsmanship of all Stoddart models. It was one of the most revolutionary receivers of the product line as well as one of the most bizarre radio receivers ever made. The NM-40A was the first "audio-spectrum-only" radio receiver, a scientific instrument that extended downward the detectable and measurable RF spectrum to 30 Hertz! The only other audio-spectrum-only radio receiver located by the author is the Empire NM-315, a 1963 transistor model that tuned from 20 Hz to 15 kHz.

In addition to being a narrowband, tunable superheterodyne (.1 v sensitivity @ 100,000 ohms), the NM-40A also could be operated as a broadband receiver (10 v sensitivity) for such signals as man-made RFI, natural ELF or VLF whistlers and atmospherics. The NM-40A was equipped to receive separately the electrical and magnetic components of a radio wave, and it included the precision detector and metering system that are basic features of a research receiver.

The NM-40A is a single-conversion superheterodyne with many novel features. It may have been the first radio receiver with a double-balanced crystal quad mixer. Its sensitive, untuned RF amplifier is housed in a rubber-suspended, Mumetal shielded compartment with additional Mumetal shields surrounding each of its three tubes. The receiver's local oscillator is a Wein bridge type and, also, is housed in a separate Mumetal shielded compartment. The 25 kHz IF section contains four stages, each of which is a two-tube amplifier. Two elaborate rack-and-pinion assemblies connect seven individual bandwidth and equalization potentiometers to coaxial panel controls. This allows the extremely narrow IF bandwidth window of 8 Hz to 60 Hz to be continuously adjustable--perhaps another engineering first for Stoddart.

Many of the NM-40A's components are mounted on a large printed-circuit board. A built-in 400 Hz tuning fork oscillator (accurate to within +/- 0.2 Hz) is used to provide a reference signal, calibrate the frequency dial, and the output level meter. This meter is calibrated in decibels and microvolts with a full range of 140 db (.1 v to 1 v). Other features include headphone, oscilloscope, remote output meter, and chart recorder outputs; a neon lamp overload indicator; input impedances from 50 ohms to 1000 megohms (with separate inputs for the magnetic and electrical components of an RF signal) and detector functions of: average, peak, quasi-peak, and rms. The separate power supply regulates the plate voltage and includes a time delay relay to lengthen the life of the receiver's 34 tubes. An extensive array of accessories were available for the NM-40A, some of which are shown below.

The little-known Stoddart 533Rs are a set of three solid-state receivers of exquisite workmanship. The 533R-3, for example, features analog tuning: 100 MHz to 1Ghz, calibrated attenuation that is achieved with a precision Stoddart attenuator (for which the company is famous) and variable bandwidths of 2, 6, 15, and 30MHz, and triple (detector?) outputs providing "AM LOG," "AM LIN," and "FM," as well as special X-axis and IF outputs. The portrayed receiver has a serial number of "3" and appears to be either a limited production unit. I have no schematic or other information about these receivers and would welcome any help.

In 1953 Richard Stoddart was an American delegate to the International Conference on EMI held in London. In 1958 he was made an IEEE Fellow. In 1962 he retired and sold his company to Tamar Electronics. By the early 1970s it became part of Singer Instrumentation and in the late 1970s merged with Ailtech, a division of Cutler-Hammer. In 1978 Cutler-Hammar was acquired by Eaton Corporation, and in 1991 Carnel Labs aquired Eaton's EMI/RFI line of products. In spite of the mergers, the respected name, Stoddart, continued to appear on new receiver models well into the 1980s.

Stoddart did not have the field of research receivers entirely to itself. After World War II, other companies, such as Empire Devices, Fairchild Electro-Metrics, Ferris, Hewett-Packard, Polarad, Singer, and Watkins-Johnson entered the market, but Stoddart will be remembered as the pioneer company that led the way in the evolution of radio research receivers of outstanding specifications and workmanship. Its influence in the development of radio communications needs further study.

Stoddart demonstration van
Stoddart demonstration van

Stoddart 1969 RFI lab
c.1968 RFI lab
Stoddart Electro Systems
Gardena, California
NSL 1959 lab
c.1959 RFI lab
National Scientific Laboratories, Inc.
Washington, DC


Years SoldModel No.Military Equiv.Freq. RangePrice*
1944 - NM-3 & 3AOCV100 MHz - 400 MHz .
1947 - 1954NM-5 & 5ATS-587/U15 MHz - 400 MHz .
1949 - 1962+NM-10 & 10AAN/URM-614 kHz - 250 kHz .
1950 - 1951+NM-20A & 20BAN/PRM-1A150 kHz - 25 MHz .
1954 - 1966+NM-30AAN/URM-4720 MHz - 400 MHz$3250 (1966)
1950 - 1966+NM-50A & 52AAN/URM-17375 MHz - 1 GHz$3250 (1966)
1956 - 1966+NM-40A**AN/URM-4130 Hz - 15 kHz$3585 (1961)
1960 - 289-1*** . 14 kHz - 150 kHz .
1962 - NM-60AAN/URM-421 GHz - 10.7 GHz .
1962 - 1966+NM-22AAN/URM-131150 kHz - 32 MHz$3250 (1966)
c.1962 - 1966+NM-62A & 62BAN/URM-1381 GHz - 10 GHz .
1966 - 1974+NM-12T . 10 kHz - 168 kHz$5670 (1974)
1972 - 533R-1 . 1 MHz - 10 MHz .
1972 - 533R-2 . 10 MHz - 100 MHz .
1972 - 533R-3 . 100 MHz - 1 GHz .
1966 - 1974+NM-25T . 150 kHz - 32 MHz$6490 (1974)
1974 - 1979+NM-26T . 150 kHz - 32 MHz$10,450 (1979)
c.1974 - 1979+NM-65T . 1 GHz - 10 GHz$18,450 (1979)
1973 - 1979+NM-17/27 . 10 kHz - 32 MHz$14,470 (1979)
1973 - 1979+NM-37/57 . 30 MHz - 1 GHz$17,230 (1979)
c. 1976 - 1979+NM-7 & 7A . 20 Hz - 50 kHz$9560 (1979)
1977 - 1980+NM-67 . 1 GHz - 18 GHz$44,000 (1979)
2003+NM-67B . 1 GHz - 18 GHz .
2003+NM-7/60A . 20 Hz - 3 GHz$65,000 (2003)
2006+CER2018 . 20 Hz - 18 GHz .
* retail price of receivers at indicated dates without antennas or other accessories.

Photo of Stoddart NM40A accessories
** Stoddart NM40A, its AC power supply, and accessories, including a 30-inch loop antenna, remote meter, chart recorder, headphones, and a dipole antenna with its own external, two-tube, high-Z preamp.

Photo of Stoddart 289-1 and antenna
***VLF spy radio,
Model 289-1

Another innovative receiver by Stoddart with the following features: pocket-sized (4 x 3-1/4 x 1-inch), 12-transistor, superheterodyne circuit with 2 RF and 3 IF stages, BFO, five crystal-tuned frequencies (14.8, 16.0, 18.6, 19.8, and 22.3 kHz) a Collins 500 Hz mechanical filter, a miniature ferrite loop antenna and an optional long-wire antenna coupler.

loop antenna: left
receiver: center
antenna coupler: right

H. A. Favors, R. E. Bloom, & R. J. Fleischer, "Interference and the RFI Meter," INSTRUMENTS & CONTROL SYSTEMS, August 1961, pp. 1443-1449.

B. G., "Amateurs Aid Hughes on World Flight," QST, October 1938, pp. 19-20.

F. Haber & R. M. Showers, "Instrumentation for Radio Interference Measurements," ELECTRONIC INDUSTRIES, March 1961, pp. 110-116+.

Dan Hoolihan, "The Richard R. Stoddart Award: The History Behind the Award," IEEE EMC SOCIETY NEWSLETTER, No. 201, Spring 2004, pp. 30-32.



Stoddart Aircraft Radio Company, INSTRUCTION BOOK FOR NOISE-FIELD INTENSITY METER TS-587/U & TS-587A/U, NAVSHIPS 900,990, USN: Bureau of Ships, 1947.

Stoddart Aircraft Radio Company, TECHNICAL MANUAL FOR RADIO-INTERFERENCE MEASURING SET AN/URM-41, NAVSHIPS 92739, USN: Bureau of Ships, 1956.


R. P. Turner, "Amateur Radio and the Hughes Flight," RADIO, October 1938, pp. 10-13+.

1941 - c.1960

Stoddart Aircraft Radio Co.
6644 Santa Monica Blvd.
Hollywood 38, California

c.1960 - c.1972

Stoddart Electro Systems
(Div. of Tamar Electronics Industries, Inc.)
2045 W. Rosecrans Ave.
Gardena, CA 90249

c.1972 - 1978

Singer Instrumentation
5340 Alla Road
Los Angeles, CA 90066

1978 - 1991

(Div. of Cutler-Hammer/Eaton)
5340 Alla Road
Los Angeles, CA 90066

1991 - 2004

Carnel Labs Corp.
Div. of ARnellab
21434 Osborne Street
Canoga Park, CA 91304

Corrections or additions are welcome.

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Revised and updated July 2006
Copyright © 1993, 1997 H.A.Layer, all rights reserved