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New FM receiver circuit

Published on Mar 14 2011 // DIY Telephone Circuits

This article describes the use of super-regenerative FM receiver, FM receiver principle, due to adopt a high-gain micro-integrated circuits, so the circuit is simple and novel. Reception to the level of ordinary FM receiver, while overcoming super-regenerative receiver selectivity, noise and large defects, while maintaining a high sensitivity, low power consumption, circuit simplicity and low cost (component cost of less than 5 million) and so on. For the electronic hobbyist production.
The aircraft’s circuit diagram as shown.

New FM receiver circuit.

By the super-regenerative FM receiver, FM-AM conversion part of the AM detector and low discharge circuit. FM wave super-regenerative receiver, in fact, will be converted into amplitude modulation waves, while wave amplitude modulation envelope detector to get the low-frequency signals. Graph composed of transistor VTl and external components typically super-regenerative FM receiver circuit, and FM signals into amplitude modulation wave signal and the envelope detector output audio signal. Removed directly from the envelope detector R3 after the end of the audio signal amplification, the resulting audio noise is relatively large, but the worse the selectivity of the receiver.
  Therefore, this uses the emitter from the VT1 circuit in series on the sensitive high-frequency choke to a high-frequency AM signal is then amplified output audio signal detection methods to overcome these shortcomings. When VT1 work, in the form a high choke on the FM program is modulated AM signal. This signal is coupled through the transformer T1 to a special receiver micro IC1 7642 AM on the amplitude demodulation.
  This integrated circuit includes a high impedance input, three high-frequency amplification and detection output of the whole process, and the gain is greater than 70dB. The audio signal from the detector output coupling capacitor C9 to transistor VT2 low frequency amplification, the output through the headphone jack to the load CZ (headphones) listen to the radio. T2 is to prevent high-frequency choke high frequency signal and battery and other parts of the loop formation was attenuated, but the audio signal but no impediment.
  For small ceramic capacitors C6 tuning capacitor, welding required to move pieces then the A-side in the figure, the purpose is to reduce the transfer station when the body of the tuner circuit of induction. High-frequency inductor L1 of the enameled wire used F1.0mm the rod on the F5.0mm 3 laps around the bodiless made. Use high-frequency choke transformer T1 removed from the old machine in the AM-IFT micro week around the system, the original wound in the "work"-shaped enameled wire on the core removed, and then re-enameled high strength FO.07mm around the primary frequency of about 50 laps around the choke part, the secondary sensor part of the 150 laps around a regulation with the magnetic cap and outer shield can be. T2 use frequency choke ring with two holes, with F0.2mm enameled wire in each hole is made in the 10 laps around.
  First by adjusting R1 to the collector current of VT1 notes 0.3mA-0.5mA, adjust the resistor R7 to the collector current of VT2 was approximately 2mA. At this point can use the headset to listen to "Silk," the sound of running water (electrical noise), by adjusting the capacitance of C6 to listen to the FM radio station. L1-turn distance and fine-tune
T1 magnetic cap, so the best sound quality.