Antenna "fox" at 3,5 MHz. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / HF antennas
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Many "fox hunters" find it difficult to get a cardioid antenna pattern on the 3,5 and 28 MHz bands. Such a diagram is obtained only if the emf. from omnidirectional and directional antennas enter the input circuit in the same phase. In fact, between d.s. there is a phase shift of 90 ° - in an omnidirectional whip antenna emf. coincides in phase with the electric field strength, and in a directional frame - with the magnetic field strength. In order to eliminate the influence of the phase shift, the phase of one of the emfs is artificially shifted. 90°.
Turning on the antennas according to the scheme shown in the figure allows you to get a good cardioid radiation pattern. Phase shift emf. the frame at an angle close to 90 ° is carried out by tuning the L2C2 circuit to resonance.
In order for the phase shift angle to be close to 90 ° when detuning the circuit, the quality factor of the circuit should not be too large.
On the 3,5 MHz band, the frame can be made in the form of a widespread split ring design, inside of which 6 turns of wire are wound. Coils L1, L2 and L3 are wound with PEV-1 0,14 wire on a standard frame with a diameter of 4 mm with a ferrite ring glued to the end. Coil L1 contains two windings of 7 turns, L2 - 50 turns, L3 - 20-25 turns. The capacitance of the capacitor C2 is selected so as to obtain resonance at the middle frequency of the operating range.
To balance the radiation pattern, the coil L1 is wound strictly symmetrically. Setting the radiation pattern is reduced to a slight selection of the number of turns of the L3 coil.
A 28 MHz band antenna can be made in a similar way.
Author: A. Partin (UV9CO), Sverdlovsk; Publication: N. Bolshakov, rf.atnn.ru
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