Encyclopedia of radio electronics and electrical engineering / radio reception
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With this unit, you can listen to HF broadcast and amateur radio signals on a VHF broadcast receiver operating at approximately 90 MHz.
Schematic diagram of the HF converter is shown in the figure.
(click to enlarge)
The principle of operation of the converter is as follows. The radio signal from the antenna WA1 is fed to the high-pass filter C1, L1. Further, it is amplified in a cascade on VT1 and fed to a mixer assembled on a transistor VT2, and a signal from a local oscillator on a transistor VT3 is also fed to this mixer, the tuning frequency of which is 75 ... 85 MHz. A frequency equal to the sum of the local oscillator frequency and the receive frequency is allocated at the output of the mixer. The received frequency ranges from 5...15 MHz.
A wide range of parts can be used in the converter, the element ratings are not critical and can vary within small limits.
Transistors VT1 ... VT3 - KT368, others can be used with a cutoff frequency of at least 300 MHz. The circuit C1, L1 can be taken from standard HF receivers. Coils L2 and L3 are wound on a mandrel with a diameter of 5 mm and contain 6 turns of SEW wire with a diameter of 0,8 mm. As an antenna WA1, you can use a piece of copper wire with a length of at least 1 m.
Setting up the converter comes down to selecting the value of the capacitor C10 before the appearance of KB radio stations in the 90 MHz VHF band. Range tuning is carried out by a variable capacitor C9. For smooth tuning to weak signals, for example, in amateur bands, a variable resistor R10 is used.
Author: E.Barsukov
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