Radio microphone on two transistors. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Radio microphone on two transistors. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Audio equipment

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This radio microphone is assembled using only two transistors, of which VT1 serves as an audio frequency amplifier, and VT2 serves as a radio frequency generator. Due to the low output power, the range is short: reception is possible within a small room or in an adjacent one through a non-permanent partition. The schematic diagram of the radio microphone is shown in the figure.

Radio microphone on two transistors

The TON-1 headphone element is used as the VM1 microphone capsule. Resistor R2 ensures the direct current mode of transistor VT1. The amplified sound signal from the collector of transistor VT1 through the isolation capacitor C2 and limiting resistor R4 is supplied to the base of transistor VT2 for amplitude modulation of the generated radio frequency. The generator is assembled according to a circuit with inductive coupling and base modulation. From the collector of the output transistor, the signal goes to the transmitting antenna, which is used as a piece of stranded wire 1 m long.

The carrier frequency of the output signal is located in the KB-1 range free from radio stations.

The low output power of the radio microphone ensures that it does not emit radio interference. The signal emitted by the radio microphone can be received with a radio receiver having the KV-1 range.

All elements of the radio microphone circuit are placed on a printed circuit board made of single-sided foil fiberglass 1,5 mm thick, which is shown in the figure.

Radio microphone on two transistors

The generator coils are wound on a frame from the input circuits with a ferrite tuning core of any transistor receiver. Coil L1 contains 10 turns, and L2 - 3 turns of PEL wire with a diameter of 0,15 mm. Coil L2 is wound on top of winding L1.

Instead of MP26B, you can install an MP42 transistor in the radio microphone circuit, and instead of P416 - KT361B. When setting up to improve the sound quality reproduced by the receiver, you can try to select the optimal resistance of resistor R5.

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