Frequency Modulated Oscillator (for FM Transmitter)

An oscillator can be built using LC (inductor-capacitor) tank circuit. When we vary the capacity of the capacitor in LC tank circuit then the frequency of the oscillator will vary according to capacitance change.  The idea of this modulator is by employing a varactor (voltage-dependent variable capacitor) in the LC tank circuitry. As the capacitance is controlled by a voltage […]

Read more

50 kHz FM Optical Receiver

Frequency modulation (FM) can be used to transmit analog voltage level signal with good noise immunity. The transmission itself  might employs different methods, and this circuit uses free air optical medium. This optical receiver circuit is built using a L14G2 detector, two stages of gain, and a FM demodulator. To obtain better sensitivity, we can use more stages of stabilized […]

Read more

Wireless Telephone Line Spy

This is a phone bug circuit. This wireless telephone line spy circuit can be used to transmit the phone conversation to a nearby FM radio. This circuit must connected to a normal phone line.  Here is the schematic diagram of the circuit: The first transistor is turned off, if the voltage drops to less than 15v (if the telephone line […]

Read more

Two Transistors FM Transmitter

Basically, this circuit is a radio frequency (RF) oscillator that operates around 100 MHz. The audio which is picked up and amplified by the electret microphone is fed into the audio amplifier stage built around the first transistor. Output from the collector is fed into the base of the second transistor. By varying the junction capacitance of the transistor, this […]

Read more
1 2 »
1 2