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Spiral cone antenna   93491-2
Wideband surveillance antenna · 1 - 10 GHz

93491-2 is a wideband UHF/SHF conical log spiral antenna, made by Stoddard Electro Systems in Gardena (California, USA). The antenna covers 1 to 10 GHz and is intended for calibrations, EMC measurements and surveillance purposes. It is housed in a grey/blue polyester cone enclosure.

The antenna is about 375 mm long and has a diameter of 130 mm at its widest point (i.e. the rear). It has the shape of a cone, with a sharp tip at the front, as shown in the image on the right.

Close to the rear end is a mounting hole that can be used to put the antenna on a (wooden) tripod or suspend it from the ceiling. At the rear is an N-type socket that should be connected to a suitable receiver or measuring device. In many surveillance applications the antenna is used complementary to the (larger) 63490-1 that covers the 200 MHz to 1 GHz frequency range.
Small spiral cone antenna (1-10 GHz)

The design is based on the ETS-3102 — made by ETS-Lindgren in Austin (Texas, USA) — but is more rugged, as the semi-rigid feedline that forms an essential part of the construction, is fully covered by the enclosure, whilst on the original ETS-3102 it runs over the outside surface [D].

The spiral cone antenna was developed by John D. Dyson in 1958, and is described in great detail in US Patent 2,958,08, complete with full mathematical backgrounds [2]. Additional information can be found on Wikipedia [1]. Antennas of this type can be used over a very wide frequency band and their impedance is more or less constant over the entire range. For this reason, they are extremely useful for monitoring the frequency spectrum and for other surveillance applications. Because it is circularly polarized, it can receive fields in any direction (horizontal and vertical).

Small spiral cone antenna (1-10 GHz) Rear view Model plate and connection at the rear 93491-2 aside the much larger 93490-1 (200 MHz - 1 GHz) Three different spiral cone antennas
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Small spiral cone antenna (1-10 GHz)
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Rear view
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Model plate and connection at the rear
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93491-2 aside the much larger 93490-1 (200 MHz - 1 GHz)
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Three different spiral cone antennas

Known spiral log antennnas
  • Model
  • Dimensions
    375 x 130 mm Ø
  • Weight
    500 grams
  • Frequency
    1 - 10 GHz
  • Impedance
    50 Ω
  • Connector
    N-type (female)
  • Max. power
    50 Watt
  • Peak power
    100 Watt
  • VSWR
    1.6 : 1
  • Pattern
  • Polarization
    Circular (right)
  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.

  4. Model 3100 Series Conical Log Spiral Antennas, User Manual
    ETS-Lindgren, September 2002. Revision C, March 2013.
  1. Wikipedia, Spiral antenna
    Retrieved October 2017.

  2. John D. Dyson, US Patent 2,958,081
    Filed 30 June 1959.
Further information
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Crypto Museum. Created: Thursday 22 March 2018. Last changed: Thursday, 22 March 2018 - 09:45 CET.
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