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Novel FM receiver

Published on Jul 19 2010 // FM Transmitter Circuits


Novel FMreceiver

This article describes the use of super-regenerative FM receiver FM receiver principle, due to the high -gain micro- integrated circuits, it is simple and novel circuit . Reception to the level of ordinary FM receiver , while avoiding the super-regenerative receiver selectivity , noise, large, etc , while maintaining a high sensitivity, low power consumption , circuit simplicity and low cost ( component cost of less than 5 dollars) and so on. Suitable for production of electronic enthusiasts . The machine circuit diagram as shown.

By the super-regenerative FM receiver , FM-AM transform part of AM detector and low-level circuit. FM wave super-regenerative receiver is actually converted into the FM wave amplitude , while amplitude modulation wave envelope detector to get the low-frequency signals . Figure of Transistor VTl and external components typically composed of super-regenerative FM receiver circuit , and FM signals into amplitude modulation wave signal and an envelope detector output audio signal . R3 -side out directly from the envelope detector audio signal after amplification, the audio noise by relatively large , but so that the selectivity of the receiver variation . Therefore , this uses the emitter from VT1 circuit through the series of high-frequency choke on induction to high-frequency AM signal further amplified output audio signal detection methods to overcome these shortcomings . When VT1 work, choke on high-frequency FM program will be the formation of an AM modulated signal . This signal is coupled through the transformer T1 to the reception of AM -specific micro- IC1 7642 on amplitude demodulation . Piece of integrated circuit includes a high impedance input , three high-frequency amplification and detection output of the whole process , and gain greater than 70dB. Audio signal from the detector output coupling capacitor C9 to transistor VT2 low frequency amplification , CZ through headphone jack output to the load ( headphones ) to listen to radio programs. High-frequency choke T2 is to prevent high-frequency signal and battery and other parts of the loop formation was attenuated , but the audio signal Quewu impediment . For small ceramic capacitor C6 tuning capacitor , welding required to take action film in the A -side in the diagram , the purpose is to reduce the transfer to of human induced effects on the tuning circuit .

High-frequency inductor L1 F1.0mm the enameled wire used in F5.0mm the rod at around 3 laps were derived . Use high-frequency choke transformer T1 removed from the old machine in the AM-IFT in the weeks around the micro- system, the original wound in the ” workers ” shaped core on the enameled wire removed , and then re- enameled high strength FO.07mm Around the primary frequency of about 50 laps around the choke part , the secondary induction of about 150 laps around after some adjustment with magnetic cap and outer shield can . Use high-frequency choke T2 magnetic holes , enameled with F0.2mm all around in the hole made 10 laps . First by adjusting R1 to VT1 notes of the collector current of 0.3mA-0.5mA, adjust the resistance R7 to the collector current of VT2 about 2mA. Headphones can be used at this time to listen to the ” slightest ” the sound of flowing water ( electrical noise ), by adjusting the C6 of the electricity capacity to listen to FM broadcasts . Turn distance and fine-tune the L1 T1 magnetic cap , so the best sound quality .