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Conical spiral antenna   23473-G2
Wideband surveillance antenna · 1-12 GHz

23473-G2 is a wideband UHF/SHF spiral antenna, invented in 1959 by John D. Dyson in the US, and currently manufactured by BAE Systems (US). The antenna is commonly used for intercept and surveillance purposes, for example as part of an airborne intercept station, or a mobile bug sweeping system, like the Micro-Tel MSR-902C. It is also known as NSN 5985-00-921-6898.

The unit – shown on the right – is a dual element unidirectional conical spiral antenna with right hand polarization, that is fed at the tip of the cone (not at the base). It comprises the S, L and X band and is suitable for frequencies between 1.0 and 12 GHz. The cone is approx. 13.5 cm long (5.25") and is 5 cm wide at the base (2").

Although initially developed for mounting under an airplane, the antenna has meanwhile become a popular item in the technical surveillance and countermeasures (TSCM) trade, in particular for finding UHF/SHF covert listening devices (bugs).
Conical spiral antenna 1-10 GHz

The antenna was developed by John D. Dyson in 1958, and is described in US Patent 2,958,08 complete with full mathematical backgrounds [2]. It was introduced to the Army on 21 December 1965, where it received National Stock Number 5985-00-921-6898. According to the packaging, the antenna shown here, was manufactured in the first quarter of 1968. According to the public NSN database, the 23473-G2 is still being manufactured today (2017) and is still an ITAR item 1 that has to be demilitarized when it is no longer needed (i.e. destroyed), to avoid its reuse [3].

Nevertheless, antennas like the 23473-G2 do appear for sale regularly on public auction sites such as eBay, commonly for several hundred dollars. In the past, the price for a single (new) 23473-G2 antenna was between US$ 1,750 and US$ 2,720 [4]. It is currently (2017) available from BAE Systems for no less than US$ 4,035 [5]. Theoretical backgrounds of the spiral antenna can be found in a series of publications by John D. Dyson in the late 1950s and early 1960s.

  1. ITAR = International Traffic In Arms Regulations.

Conical spiral antenna 1-10 GHz Conical spiral antenna 1-10 GHz SMA socket at the bottom Text printed on the edge of the antenna
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Conical spiral antenna 1-10 GHz
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Conical spiral antenna 1-10 GHz
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SMA socket at the bottom
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Text printed on the edge of the antenna

Known spiral log antennnas
  • Type
    Dual element conical spiral antenna
  • Frequency
    1 - 12 GHz
  • Band
    S, L, X
  • Connector
  • Impedance
    50 Ω
  • Feedpoint
  • Polarization
    Circular Right
  • Part #
  • Stock #
  • NSN
  • Date
    1968 Q1
  • Length
    6.000 inches
  • Diameter
    1.969 inches
  • Mounting
    4 holes of 0.125 inches, threaded
  1. John D. Dyson, An unidirectional equiangular sprial antenna
    Technical Report No. 33, 10 July 1958.

  2. John D. Dyson, A theoretical study of the equiangular sprial antenna
    Technical Report No. 35, 12 September 1958.

  3. A Survey of the Very Wide Band and Frequency Independent Antennas —
    1945 to the Present — John. D. Dyson, 16 August 1961.
    Journal of Research of the National Burau of Standards (now: NIST).
    Volume 66D, No. 1, January-February 1962.
  1. Wikipedia, Spiral antenna
    Retrieved October 2017.

  2. John D. Dyson, US Patent 2,958,081
    Filed 30 June 1959.

  3. NSN Info, NSN 5985-00-921-6898
    Registered 21 December 1965. Retrieved October 2017.

  4. AeroBase Group, Antenna 23473G2
    Retrieved October 2017.

  5. Computer Locators, Price List
    Retrieved October 2017.
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Crypto Museum. Created: Friday 20 October 2017. Last changed: Wednesday, 21 March 2018 - 23:36 CET.
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