Download Powerful AM transmitter Click here for the circuit diagram

Powerful AM transmitter
Click here for the circuit diagram
The circuit for a powerful AM transmitter using ceramic resonator/filter of 3.587 MHz is
presented here. Resonators/filters of other frequencies such as 5.5 MHz, 7 MHz and 10.7 MHz
may also be used. Use of different frequency filters/resonators will involve corresponding
variation in the value of inductor used in the tank circuit of oscillator connected at the collector of
transistor T1.
The AF input for modulation is inserted in series with emitter of transistor T1 (and resistor R4)
using a transistor radio type audio driver transformer as shown in the circuit. Modulated RF
output is developed across the tank circuit which can be tuned to resonance frequency of the
filter/resonator with the help of gang condenser C7. The next two stages formed using low-noise
RF transistors BF495 are, in fact, connected in parallel for amplification of modulated signal
coupled from collector of transistor T1 to bases of transistors T2 and T3. The combined output
from collectors of T2 and T3 is fed to antenna via 100pF capacitor C4.
The circuit can be easily assembled on a general-purpose PCB. The range of the transmitter is
expected to be one to two kilometers. The circuit requires regulated 9-volt power supply for its
operation. Note: Dotted lined indicates additional connection if a 3-pin filter is used in place.