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Spiral cone antenna   93490-1
Wideband surveillance antenna · 200 MHz - 1 GHz

93490-1 is a wideband VHF/UHF conical log spiral antenna, made by EATON/AILTECH/SINGER in Los Angeles (California, USA). It covers 200 MHz to 1 GHz and is intended for calibrations, EMC measurements and surveillance purposes. It is housed in a green/blue polyester cone enclosure.

The antenna is about one metre long and has a diameter of 35.5 cm at its widest point (i.e. the rear). It has the shape of a cone, with a flat top at the front, as shown in the image on the right.

About 1/3rd from 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 (smaller) 23473-G2 that covers the 1 to 12 GHz range.
  
EATON spiral cone antenna 93490-1

The design is based on the ETS-3101 — 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-3101 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).

EATON spiral cone antenna 93490-1 Rear view EATON spiral cone antenna 93490-1 (200 MHz to 1 GHZ), next to a 23473-G2 spiral antenna (1 - 12 GHz) Rear view of 93490-1 (200 MHz - 1 GHz) and 23473-G2 (1-12 GHz) EATON spiral cone antenna 93490-1 (200 MHz to 1 GHZ), next to a  in front of a 23473-G2 spiral antenna (1 - 12 GHz)
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EATON spiral cone antenna 93490-1
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Rear view
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EATON spiral cone antenna 93490-1 (200 MHz to 1 GHZ), next to a 23473-G2 spiral antenna (1 - 12 GHz)
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Rear view of 93490-1 (200 MHz - 1 GHz) and 23473-G2 (1-12 GHz)
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EATON spiral cone antenna 93490-1 (200 MHz to 1 GHZ), next to a  in front of a 23473-G2 spiral antenna (1 - 12 GHz)

Known spiral log antennnas
  • 93490-1
    200 MHz - 1 GHz
  • 93491-2
    1 - 10 GHz
  • ETS-3101
    200 MHz - 1 GHz
  • 23473-G2
    1 - 12 GHz
  • 11966G
    1-10 GHz (Keysight)
Documentation
  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.
References
  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: Monday 04 December 2017. Last changed: Tuesday, 05 December 2017 - 08:54 CET.
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