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Old Receiving Magnetic Loop Antennas

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ANTENTOP- 02- 2004, # 006   Old Receiving Magnetic Loop Antennas





Igor Grigorov, RK3ZK


Receiving magnetic loop antennas were widely used in the professional radio communication from the beginning of the 20 Century. Since 1906 magnetic loop antennas were used for direction finding purposes needed for navigation of ships and planes. Later, from 20s, magnetic loop antennas were used for broadcasting reception. In the USSR in 20- 40 years of the 20 Century when broadcasting was gone on LW and MW, huge loop antennas were used on Reception Broadcasting Centers (see pages 93- 94 about USSRs RBC). Magnetic loop antennas worldwide were used for reception service radio stations working in VLW, LW and MW. The article writes up several designs of such old receiving loop antennas.



LW- MW Huge Receiving Loop Antennas for Broadcasting and Direction Finding


In old radio textbooks you can find description of old magnetic receiving loop antennas. As a rule, old magnetic receiving loop antennas had a triangle or square shape, a side of the triangle or square had length in 10-20 meters. The huge square was put on to a corner. The distance from the ground up to lower wires of the magnetic receiving loop usually was not less than 4 meters. Fig. 1A shows a triangular receiving loop antenna consisting of two perpendicular loops, used for direction finding at airports [1], Fig. 1B shows a square receiving loop antenna used on Broadcasting Radio Centers of the USSR at the end of 30s of the 20 Century [15]. Usually the receiving magnetic loop contained from one up to eight turns.



Fig. 2 shows a typical connection of the above mention huge magnetic receiving loop antennas designed for working on one fixing frequency to the receiver. To a resonance the loop A1 is tuned by lengthening coil L1 (sometimes two lengthening coils switched symmetrically to both side of the loop were used) and variable air- dielectric capacitor C1. T1 did connection with antenna feedline. L1, C1 and T1, as a rule, are placed directly near the antenna keeping minimum length for wires from the antenna to the parts. Certainly, there were others circuits for connection magnetic loops to a receiver, but the circuits were insignificantly distinguished from Fig. 2.


Small- Sized Magnetic Loop of a Local Broadcasting Radio Center


Huge loop antennas were used for cities Broadcasting Radio Centers, for local Broadcasting Radio Centers a small- sized loops were used.




Figure 1A Old huge magnetic receiving loop antennas

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