Antenna for 7 MHz with low suspension height. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / HF antennas
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The loop antenna "DELTA LOOP", located in such a way that its upper corner is at a quarter-wave height above the ground, and power is supplied to the loop break in one of the lower corners, has a large level of radiation of a vertically polarized wave under a small one, of the order of 25-35 ° angle relative to the horizon, which allows it to be used for long-distance radio communications [1].
A similar emitter was built by the author, and its optimal dimensions for the 7 MHz band are shown in Fig. 1.
The input impedance of the antenna, measured at 7,02 MHz, is 160 ohms, therefore, for optimal matching with a transmitter (TX) having an output impedance of 75 ohms, a matching device was used from two quarter-wave transformers connected in series from coaxial cables 75 and 50 ohms (Fig. 2). The antenna impedance is transformed first to 35 ohms, then to 70 ohms. The SWR does not exceed 1,2. If the antenna is more than 10 ... 14 meters away from the TX, a coaxial cable with a characteristic impedance of 1 Ohms of the required length can be connected to points 2 and 2 (Fig. 75). The dimensions of the quarter-wave transformers shown in Fig. 2 are correct for cables with polyethylene insulation (shortening factor 0,66).
(click to enlarge)
The antenna was tested with an 8W ORP transmitter. Telegraph QSOs with hams from Australia, New Zealand and the USA confirmed the effectiveness of the antenna when working on long distances. Additional information on tuning and measuring antenna parameters can be found in [2].
Literature
1. Z. Benkovsky, E. Lipinsky. Amateur antennas of short and ultrashort waves. Moscow 'Radio and communication', 1983, translated from Polish.
2. K. Rothammel. Antennas. Moscow "Energy" 1969 trans. from German.
Author: Igor Zakharov, UR5EFX, Dnepropetrovsk; Publication: N. Bolshakov, rf.atnn.ru
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