FM Transmitter with two Transistor

A lot of FM transmitter circuits accept been already appear here. This just addition one, a simple two transistor FM transmitter. The aboriginal date of the circuit is a preamplifier date based on transistor Q1. This is a beneficiary to abject biased amplifier date area resistor R2 sets the beneficiary accepted and R1 provided the all-important beneficiary to abject bias. C1 is the ascribe DC decoupling capacitor which couples the ascribe audio arresting to the Q1 base. C8 is the ability accumulation by-pass capacitor.

Next date is the oscillator cum modulator date congenital about transistor Q2. Electrolytic capacitor C2 couples the achievement of the aboriginal date to the additional stage. R3 and R4 are the biasing resistors of Q2. R5 is the emitter resistor of Q2. Inductor L1 and trimmer capacitor C5 forms the catchbasin ambit which is all-important for creating oscillations. The articulate FM arresting is accessible at the beneficiary of Q2 and it is accompanying to the antenna application capacitor C9.

Notes.

• The circuit can be powered from anything between 6 to 12V DC.
• Using battery for powering the circuit will improve the performance and reduce noise.
• A 9V PP3 battery is a good option.
• If you are going with a battery eliminator, then it must be well filtered and regulated.
• Trimmer C5 can be used for adjusting the transmission frequency.
• Antenna can be a 1m copper wire.
• L1 can be constructed my making 4 turns of 1mm enameled copper wire on a 10mm diameter plastic former.
• Trimmer capacitor C6 can be adjusted for obtaining the maximum range.
• Most of the components required for this circuit can be procured from your junk box.

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BH1417 PLL FM Stereo Transmitter

The circuit shown here is Stereo FM transmitter which will transmit high quality signals up to a range of 70 feet. The circuit is based on BH1417 PLL stereo transmitter IC from Rhom semiconductors. The IC has separate audio processing sections for the left and right channels, pre emphasis circuit for improving signal to noise ratio, crystal control circuitry for correct frequency locking, multiplex circuit for creating sum ( left and right) and difference ( left minus right).

Another vital feature of this IC is that the transmission frequency can be set employing a 4 channel DIP switch. The IC can be powered from something between 4 to 6V DC and has an output power around 20mW. At full output power the circuit consumes only 20mA and has a channel separation of 40dB. There are 14 potential preset transmission frequencies, starting from 88.7MHz and incrementing in steps of 0.2MHz that can be selected using the DIP switch. The PLL circuitry of the IC is so precise that there's practically no frequency drift.

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88-108 MHz FM Broadcast Transmitter

88-108 MHz FM Broadcast Transmitter circuit

This circuit will transmit a continuous tone audio FM broadcast band (88-108 MHz) which could be used for remote control or security. Circuit draws about 30 mA with a 6.9-volt battery and can receive about 100 meters. A 555 timer is used to produce the tone (about 600 Hz), which modulates the frequency of a Hartley oscillator. A second JFET transistor buffer stage is used to isolate the oscillator from the antenna to the antenna position and length has less effect on the frequency.

Fine adjustment can often be done by adjusting the 200 Ohm resistor in series with the battery. Oscillator frequency is set by an inducer of turn 5 and 13 pF capacitor operated. The inductor is wound around a # 8 x 32 bolt (about 3 / 16 in diameter) and then removed by unscrewing the screw. The inductor was then streached to about a length of 3 / 8 inches and hit near the center. The oscillator frequency should come out somewhere near the center of the band (98 MHz) and can be moved up or down slightly the expansion or compression of the coil.

A small signal diode (1N914 or 1N4148) is used as a varactor diode so that the total capacity in parallel with the coil varies slightly in the type of audio causing the oscillator frequency to change the audio rate (600 Hz) . The ramp waveform at pins 2 and 6 of timer applies to the reverse diode across a large bias (1 Meg) resistor so that the capacity of the diode changes as voltage changes thus increasing altering the frequency of tank circuit.

Alternatively, an audio signal could be applied to the 1 Meg resistor to modulate the oscillator but may require a pull-up resistor to reverse bias additional diode. The N channel JFET transistors used should be high frequency VHF or UHF types (Radio Shack # 276-2062 MPF102) or similar.

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