Consider the inclusion of a loop antenna on the example of radio "Ocean" with a drum switch ranges. A fragment of the circuit shown in Fig.1 . All sectors need to switch release pin 18 (K18). Disconnected from the circuit should be connected to pin 6. Fixed lamella contact 18 also need to disconnect from the body and into the fracture to enable the loop antenna, which is a single turn of wire of arbitrary shape, is laid around the perimeter of the chassis so as to obtain the maximum area of the coil. You can use any copper wire with a diameter of 0,3...0,5 mm.
In the ranges of 50, 31 m frame is connected in series with the coil circuit, it is necessary to disconnect the output contour coil from KB and connect to K18 (figure 2). After that, the input circuit to adjust on the long wavelength area of each range to the maximum signal, when unscrewing the core contour of the coil.
In the range of 25 m and above this enabling framework leads to the increase of the inductance of the circuit, which could not be compensated ferrite core. In these ranges, the frame is included in the circuit through the capacitors stretching range. For this purpose, the capacitor C14 capacitance 300 pF in the range of 25 m disconnect from K6 and switch to K18 (Fig 3). The tuning of the input circuit is carried out as usual.
Describes how to enable loop antenna ensures maximum efficiency, because at any range it is an integral part of the resonant circuit in the input circuit. In the same way, the frame may be included in any radio with its circuitry the efficiency of the loop antenna with this method of inclusion is not worse telescopic, and the radio interference is dramatically improved.
Ham 12/2000, p. 3
Publication: N. Bolshakov, rf.atnn.ru