With this simple radio transmitter, you can go on the air at a frequency of 27 MHz.The modulation is amplitude, the output power at a load of 50 ohms is 300 mW with a power supply of 17 volts.
The transmitter is made on a KN2222A transistor, the modulator on a KSE800 transistor.The frequency of the transmitter is set by a quartz resonator.But we must take into account that there are resonators that work on harmonics, they cannot be used in this transmitter.
Coils L1 and L2 are wound on a frame with a diameter of 5 mm with a ferrite core.L1 contains 15 turns of 0.3mm wire. L2 is wound on top of L1 and contains 4 turns of 0.3mm wire.
Customization.If you do not have devices for tuning, then connect a 47 ohm resistor to L2, it is a load.By adjusting the ferrite core, achieve maximum heating of the resistor.If it heats up, it means the transmitter is working and probably gives maximum power.
The device shows an output power of 300 mW at a load of 50 ohms
Connect the RF probe to the L2 pins, the probe LED should be shining brightly
The antenna is a 27 MHz dipole.Each arm of the dipole has a length of approximately 255 m .A 50 ohm coaxial cable is connected to the dipole.When the transmitter is in operation, the RF probe will shine brightly near each arm of the antenna.The maximum brightness will be at the end of each arm of the antenna.The brighter the LED shines from the antenna, the maximum power of the transmitter goes to the antenna.This means that there will also be a maximum range of broadcasting of the transmitter.
With the Tecsun Pl-600 radio receiver, I walked about 700 meters and the receiver still received the signal, I did not go further.
