VHF radio receiver on the chip KHA058. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / radio reception
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Two years ago, we had a KXA-058 chip on sale. On its basis, I made a VHF radio receiver, the circuit of which I present to your attention. The receiver was conceived to work on headphones from the player. It is minimal in size and easy to carry in the breast pocket of a jacket or shirt. Since the microcircuit consumes a relatively large current (8 ... 14 mA), I used three cylindrical batteries 14 x 50 mm in size as a power source. The rest of the circuit was chosen taking into account the reduced supply voltage and low current consumption. The K538 UNZA chip was used as a ULF. It provides enough power to the load.
To match the microcircuit with a low-resistance load, it is necessary to connect a 100 Ohm resistor in series with it. To work on a loudspeaker, you can use the K157UD1 chip. Both microcircuits remain operational when the supply voltage drops to 3 V. To tune the receiver in range, a KV134AT varicap is used (KV132AT can be used), which is connected to the local oscillator circuit through an isolation capacitor. As such a capacitor, I used a free chip capacitor between its third and fourth legs.
(click to enlarge)
To stabilize the reference voltage of the varicap, a micropower stabilizer circuit based on three transistors is used. Transistor VT3 must be germanium. All this complicates the circuit a little, but it is much more economical and stable. The stabilization coefficient is approximately 10. The stabilization voltage can be changed from 1,5 V to 2 V without a noticeable deterioration in the stabilization coefficient by selecting the resistor R7. With the ratings indicated in the diagram, the reference voltage is 2 V. The inductor in the local oscillator circuit contains 14 turns of 0,4 mm PEV wire wound turn to turn on a 6x6 mm ribbed frame with a ferrite trimmer with a diameter of 3 mm. The tuning element is a resistor R6 type SPZ-36, etc. Such a resistor is convenient in that it is miniature, multi-turn and has a slider with a label that can be used as a scale.
Publication: cxem.net
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