USAP Aperiodic Loop Antenna


USAP-Aperiodic-Loop-Antenna-data-sheet-1Our basic antenna is an untuned, balanced loop which has dimensions that are small compared with the wavelength. A preamplifier circuit, fitted at the base of the antenna, exactly complements the loop characteristics. This combination results in a nominally constant, effective, height over the 2.0 to 32.0 MHz frequency range.
At frequencies less than 30.0 MHz it is possible to employ an antenna for receiving purposes which is electrically small and has poor free-space coupling efficiency, without prejudicing the overall system noise factor. This is because the antenna output noise comes primarily from atmospheric and galactic sources. The thermal noise introduced by the antenna radiation resistance is insignificant by comparison, if this resistance is presumed to be at ambient temperature.
While a requirement for free-space coupling efficiency remains for a transmit antenna, it does not for the receive antenna. The aperiodic loop antenna configuration includes loop/preamplifier elements, in an “end fire” array, with an interconnecting transmission line coupling each element. The element spacing has been carefully chosen to provide optimum directional characteristics for both long and short haul, point-to-point HF communication using the ionosphere. Outputs are available at both ends so the array can look both ways simultaneously, if required, or can be rapidly switched through 180° with a coaxial relay.
The loop, with its vertical plane, is mounted close to the ground in terms of wavelength to obtain additional incident and reflected signals. The loop element is a welded assembly of aluminum alloy weighing only 10 pounds, and may be mounted on a tripod or bolted to a post with an angle bracket.


  • Operating Range 2.0-32.0 MHz
  • Small Size
  • Rugged Construction
  • Easily Installed
  • Fixed and Transportable Versions
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