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HE-100
Portable active directional antenna

The EH-100 was a set of portable active antennas, developed by Rohde & Schwarz in München (Germany) in the 1980s. The antenna set was used for locating interferences and radio bugs, and was initially developed for use in combination with the EB-100 portable surveillance receiver.
 
The HE-100 is suitable for all frequencies from 20 MHz to 1 GHZ and consists of a handheld pre-amplifier in the shape of a pistol grip, and three plug-on antenna's. Each of the antennas covers a different frequency range. The pre-amplifier is powered by internal batteries and is activated by pressing a trigger switch in the grip.

The three antenna's use the terminated loop principle developed in 1938 by Harold Beverage in the USA [1] [2]. Due to the nature of these antennas they are far less sensitive to signal reflections, especially when used indoors.
  
The 500-1000 MHz antenna in action

For storage and transport, the three antennas are usually packed inside a purpose built executive style briefcase, together with the pistol-grip pre-amplifier, the instruction booklet [3], spare batteries and any other accessories. The antennas cover the following frequency ranges:
 
The antennas were designed to match the frequency coverage of the EB-100 from 20 MHz to 1 GHz. For most bugs of the 1980s, the largest antenna (20-200 MHz) was used.

In practice, the middle antenna (200-500 MHz) could also be used when in close proximity of the transmitter. It made the antenna slightly less sensitive but that was often considered a bonus.
  
20-200 MHz HE-100 antenna connected to the EB-100 receiver

When using the HE-100 in combination with the EB-100 reciver, the field strength meter at the rear of the HE-100 would show the signal strength of the signal, duplicated from the signal strength indicator of the EB-100. The meter could also be used to test the HE-100's batteries.
 
When the HE-100 antenna and the EB-100 receiver were used in the dark, the meter could be illuminated by pressing a second switch in the pistol grip of the HE-100 (i.e. the lower one).

Although the HE-100 antenna was initially designed for use in combination with the EB-100 receiver, it could very well be used with other TSCM devices, such as the Rohde & Schwarz FSH-3 portable spectrum analyser shown here.

 More about the FSH-3
  
FSH-3, HE-100 antenna and a ATET radio bug at 135 MHz

The HE-100 antenna was later superceeded by the HE-300 active directional antenna, which has an extended frequency range from 20 MHz to 7.5 GHz. At the lower end, the frequency range can be further extended down to 9 kHz by adding the optional HE-300-HF module.
 
Executive style briefcase holding the three HE-100 antennas Contents of the bottom half of the briefcase 20-200 MHz antenna 200 - 500 MHz antenne 500 - 1000 MHz The pistol grip with built-in pre-amplifier The pre-amplifier (right) and the 500-1000 MHz antenna The 500-1000 antenna ready for use
Close-up of the 500-1000 MHz antenna The connector of the 20-200 MHz antenna 20-200 MHz HE-100 antenna connected to the EB-100 receiver The 500-1000 MHz antenna connected to the EB-100 FSH-3 with HE-100 (20-200 MHZ) The FSH-3 with an FM radio bug at 203 MHz and a span of 10 MHz FSH-3, HE-100 antenna and a ATET radio bug at 135 MHz FSH-3, HE-100 antenna and a ATET radio bug at 135 MHz

 
References
  1. US Patent 2247743, Broadband Uni-directional Shortwave Antenna
    Harold H. Beverage. Filed 10 December 1938.

  2. DARC Verlag, Rothammels Antennenbuch
    ISBN: 3-88692-033-X. 2nd print 2002. p. 269-270.

  3. Rohde & Schwarz, Active Directional Antenna HE-100
    652.1803.02 (German/English). March 1986.

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