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    The FM modulator circuit (frequency modulation) is built with a Motorola MC1648P oscillator. Two varactors, Motorola MV-209 are used to frequency modulate the oscillator. The 5000 Ω potentiometer is used to bias the varactors for the best linearity. The output frequency of approximately 100 MHz can be adjusted by changing the value of the inductor.

    The output frequency can vary as much 10 MHz on each side. The output level of the modulator is -5 dBm. In this fm modulator prototype the varactor bias was 7.5V for the best linearity but this could be different with other varactors.

    FM modulator circuit diagram

    fm modulator circuit schematic

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    18 Responses to "FM Modulator Circuit"

    1. please can I get circuits that generated FM modulation with or without ICs

    2. i need project report of this model

    3. this project is so good to present… cn i get project report of this model??

    4. i need full circut digram of fm modulator

      • ElectroSchematics.com says: on February 2, 2010 at 3:35 pm

        Jaspreet – if you look in the article there is the fm modulator circuit diagram, it is built with MC1648P from Motorola.

    5. please i need a complete circuit diagram for fm radio kit

    6. please i need a complete circuit diagram for a one transistor radio kit

    7. i love the website with it’s explanation of reseach. i’ll like to “frequency modulator circuit diagram with details” thanks so much.

    8. Please, i need component list of this circuit.Thank

    9. i need a fm audio loss alarm circuit,when a particular fm station is off at working an alarm will produce.kindly send anybody know the circuit diagram

    10. is the IC#1 the circuit as known as 555 ?

    11. what is ic#1????

    12. karan, integrated circuit nuber#1 is Motorola MC1648P chip.

    13. your efforts are appreciatable

    14. mujy polarity samaj mein nhn a rahi kia karoon????????

    15. Hi folks, for those of you who want to look at a good site, i suggest http://www.sm0vpo.com/ (ultimate site for learners and experienced alike.) Dont send him silly questions though. From a one tranny circ. to more elaborate transmitters such as V7b and v7
      Here you will all find the circuits and theories behind radio circuits which are simple to follow.
      As you can see above, there is a coil with two tuning diodes(mv209, 2 x bb105 or similar may work too) (find, the veronica 1 watt guys , similar tuning deal) the mc1648 chip is a stabiliser type chip regulated by the 5v zener, although you will find that this was quite a stable circuit without if the circuit ran off say a 9v regulator, the earliest model i can think of was a kids c.b circuit and then the 3w pantek came from that (good sound , rubbish harmonics but stable). This is prone to harmonics with out the chip and a filter though. This will not propogate more than one room i would say. I see no amplification either. This should put out the few miliwatts that could be amplified.

      • That site name again, sm0vpo.com typo in my above comment. thats a zero in the middle. sorry bout that.

      • Alexpmgr8 i want to learn about Antenna very interested in Radios and Antennas, please refer me any excellent site about Antennas.

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