FM Modulator Circuit

Posted on Feb 6, 2014

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 © 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 inducto

FM Modulator Circuit
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r. 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. Hi folks, for those of you who want to look at a good site, i suggest (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 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.

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