Series Modulated AM Transmitter
A series modulated AM Transmitter is a type of radio transmitter that uses amplitude modulation (AM) to transmit audio signals over a carrier wave. It’s known for being low-power and simple to construct, making it a good option for beginners or those interested in QRP (low-power) applications. In a series-modulated AM transmitter, the audio signal is directly added in series with the power supply of the RF oscillator stage. This causes the amplitude of the RF carrier to vary in accordance with the audio signal, creating an AM wave.
In this circuit, oscillator is crystal controlled. By changing different frequency crystal, one can vary frequency of transmitter. Keep in mind that the oscillator output waveform is square wave, which is rich in harmonics. With appropriate matching and filtering, it can be used as a small broadcasting station.Set the potentiometer VR1 (10k) on it so that 6.6 volts are present at the collector of the Q5 in the modulator without any audio signal applied to it. The R7 should be 100 ohms 2 watts resistor.
Building a series-modulated AM transmitter can be a fun project for electronics enthusiasts and a great way to learn about the basics of AM radio transmission. However, it’s important to remember that regulations govern radio transmission in most countries. You’ll need to comply with the regulations in your area before operating a homemade transmitter. This circuit is modified version of mini AM transmitter