Fm Transmitter Ic | Electronic Project Circuits

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Coil-less FM Transmitter by IC 40106

The RF oscillator using the inverter N2 and 10.7Mhz ceramic filter is driving the parallel combination of N4 to N6 through N3.Since these inverters are in parallel the output impedance will be low so that it can directly drive an aerial of 1/4th wavelength. Since the output of N4-N6 is square wave there will be a lot of harmonics in it.
More information about IC CD40106

The 9th harmonics of 10.7Mhz (96.3Mhz) will hence be at the center of the FM band. N1 is working as an audio amplifier. The audio signals from the microphone are amplified and fed to the varycap diode. The signal varies the capacitance of the varycap and hence varies the oscillator frequency which produce Frequency Modulation.

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Categories: FM transmitter, RF-Radio Frequency Tags: CD40106, FM transmitter, fm transmitter ic

FM Transmitter with Op-amp

This is FM Transmitter with Op-amp LM358. It is basic circuit for all user.

Parts List:
R1 4K7 R4 150K R7 3K9 (2K7)
R2 4K7 R5 220R R8 120R (82R)
R3 4K7 R6 4K7

All resistors except R8 are at least 0.25W rated. R8 is at least 0.5W rated
(the 0.6W metal film M-series from Maplin can be used for R1-R8).

C1 1n C4 22uF C7 10n C10 1n
C2 4u7 C5 1n C8 1n
C3 1n C6 10n C9 33pF
VC1 5-60pF IC1 LM358 Q1 ZTX108

Notes:
L1 is 0.112uH (this tunes to the middle of the FM band, 98 MHz, with VC1 at its centre value of 33pF). L1 is 5 turns of 22 swg enamelled copper wire close-wound on a 5mm (3/16″) diameter former. Alternatively, you can have a fixed 33pF cap instead of VC1 and have L1 as an adjustable molded coil (eg UF64U from Maplin). VC1 will give you a tuning range of 85 – 125 MHz, and a possible choice is the Philips type polypropylene film trimmer (Maplin code WL72P). Two sets of oscillator bias resistors are given, the ones in the brackets give about 20% more RF power. Mike is our favourite Omnidirectional sub-mini electret (Maplin code FS43W). Ant is a (lambda / 4) whip monopole (eg 76 cms of 22 swg copper wire). Q1 is configured as a Clapp oscillator. Frequency modulation results from the audio voltage changing the transistor’s base-emitter capacitance.