IONOSPHERIC-SOUNDER MEASUREMENT OF RELATIVE GAINS AND BANDWIDTHS OF SELECTED FIELD-EXPEDIENT ANTENNAS FOR SKYWAVE PROPAGATION AT NEAR-VERTICAL INCIDENCE.
Special technical rept.,
STANFORD RESEARCH INST MENLO PARK CA
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Several methods developed for measuring the performance of HF antennas used on short ionospheric paths at or near vertical incidence are described. Examples of such measurements are given, in which selected field-expedient antennas are compared. Ionospheric-sounder studies show the superiority of a half-wave horizontal dipole, placed less than lambda4 above ground level, over the slant-wire and inverted L antennas for propagation at or near vertical incidence at 6 Mcs. Measurements of the effect of antenna height and of a balun on impedance and bandpass characteristic are presented and discussed. Measurements of the effect of a metallic ground screen and of dipole-antenna and feed-line sag on the response of the antenna are presented and discussed. Preliminary results indicate the following 1 The one-way gain at the zenith of a half-wave dipole at a height of lambda8 exceeds that of a 30 degree slant-wire by more than 12 dB, and that of a 51 inverted L by more than 8 dB. 2 Lowering the dipole to a height of lambda10 over good ground decreases the vertical gain by 3 dB or less. 3 A balun makes little difference in the performance of a transmitting resonant dipole. 4 At a height of lambda4, the elements of a half-wave dipole may sag or its feed line may be displaced by 45 degree before the gain drops 3 dB. Author
- Radio Communications