Monday, October 31, 2011

Simple AM Transmitter Circuit

AM transmitter circuit that can transmit your audios to your backyard.This circuit is designed with limited the power output to match the FCC regulations and still produces enough amplitude modulation of voice in the medium wave band to satisfy your personal needs. You will love this. 

The circuit has two parts , an audio amplifier and a radio frequency oscillator. The oscillator is built around Q1 (BC109) and related components. The tank circuit with inductance L1 and capacitance VC1 is tunable in the range of 500kHz to 1600KHz. 

These components can be easily obtained from your old medium wave radio. Q1 is provided with regenerative feedback by connecting the base and collector of Q1 to opposite ends of the tank circuit. C2 ,the 1nF capacitance , couples signals from the base to the top of L1, and C4 the 100pF capacitance ensures that the oscillation is transfered from collector, to the emitter, and through the internal base emitter resistance of the transistor Q2 (BC 109) , back to the base again. 

The resistor R7 has a vital part in this circuit. It ensures that the oscillation will not be shunted to ground trough the very low value internal emitter resistance, re of Q1(BC 109), and also increases the input impedance such that the modulation signal will not be shunted to ground.

Q2 is wired as a common emitter RF amplifier, C5 decouples the emitter resistance and unleashes full gain of this stage. The microphone can be electret condenser microphone and the amount of AM modulation can be adjusted by the 4.7 K variable resistanceR5.

Saturday, October 8, 2011

AM Receiver Circuit Diagram Using ZN414 IC

A.M. Antenna coil and MW gang connected in parallel. One common point of this parallel circuit connected to the IC ZN414 pin number 2.

Another common point of that parallel circuit connected with two resistors (100kΩ, 1kΩ) in series. A capacitor is connected with the common point of resistors (100kΩ, 1kΩ).  A capacitor is connected in series with base of the transistor and the pin number 1 of the ZN414.
One end of the 10kΩ resistor is connected with the collector point of the transistor BC549 and another end is connected with the power supply +Vcc.

And one end of the 100kΩ resistor is connected with the collector and another end connected with base. 105pF capacitor is connected between collector and ground. Pin 3 of IC ZN414 and emitter of the transistor is connected to the ground.

 Required Instrument
  • IC ZN 414.
  • Capacitor(105pF×1,104pF×2,103pF×1)
  • MW Gang
  • Resistor(100kΩ×2,10kΩ×1,1kΩ×1,470Ω×1)
  • AM antenna
  • Transistor(BC549)