DIY transmitter 27 MHz.Power output 5Watt

With this radio transmitter, you will be able to conduct radio communication at a great distance.Amplitude modulation, output power of about 5 watts,power supply of 13.5 volts, current consumption of about 1.7 amps.

The coil L1 contains 15 turns of wire with a diameter of 0.3 mm wound on a frame with a diameter of 5mm
The throttle L2 has an inductance of 10 µgn and a wire diameter of 0.5mm
The throttle L3 contains 15 turns of wire with a diameter of 0.5 mm wound on a ferrite with a diameter of 6 mm.Such ferrite can be taken from the throttle of computer power supplies
The L4 coil contains 13 turns of wire with a diameter of 0.7 mm and an inner diameter of 6mm

Setting up the generator on the kn2222 transistor.The quartz resonator is not for a 27 MHz harmonic (there are quartz harmonics), but for a frequency of 27 MHz.Put a load resistor with a resistance of 47 ohms between the capacitor C4 and the ground.Connect the oscilloscope to the resistor and you will see a sine wave with a span of 1.12Volts

If you don’t have an oscilloscope, then just turn on the radio and you will hear silence at a frequency of about 27 MHz.

Now the setup of the preamp on the BD139 transistor.The transistor is mounted on a small radiator.Install a 47 ohm resistor between the capacitor C6 and the ground.On the oscilloscope you will see a 9.12 Volt sine wave.

If you do not have an oscilloscope, put an incandescent lamp with a voltage of 12 volts and a current of about 150mA instead of a 47 ohm load resistor.The lamp should glow (bright or not depends on the resistance of the filament).Also check the signal with the radio receiver.Instead of a lamp, you can install a 47 ohm 0.5W resistor.If the resistor gets very hot, then everything is fine

Now the setting of the power amplifier on the IRF610 transistor.Parallel to the capacitor C8, install an incandescent lamp with a power of 10 W and a voltage of 12 Volts.Install the variable resistor rotor in the middle.By rotating the rotor of the variable capacitor, achieve the maximum brightness of the lamp.Next, with the variable resistor R6, also achieve the maximum brightness of the incandescent lamp.Change the resistance of the variable resistor slowly.Make sure that the current consumption is about 1.6-1.8 Amperes at 13.5 Volts and the lamp shines brightly.

Next, instead of a lamp, install a 47 ohm load resistor and connect an oscilloscope to it to observe the signal.

On the oscilloscope screen you will see a sine wave with a span of about 70-80 Volts (the oscilloscope divider probe is set to *10).The sine wave should be without distortion.

Apply sound to the capacitor C5.Transistor 2SK3570 is a modulator that modulates the power current of the transistor BD139.
ATTENTION:do not use sensitive electronics as a sound source, as there is a high-frequency current in the transmitter that can disable the sound chip in the phone.To reduce the high-frequency current, put the chokes to the capacitor C5 and ground.
In the receiver, you should hear a clear sound signal without significant distortion.The sine wave should oscillate up and down.This is the amplitude modulation signal.

The transmitter is set up.Now, instead of a resistor and an incandescent lamp, you need to connect an antenna, which is also a load.Without load, the transmitter WILL NOT TURN ON, otherwise BD139 or IRF610 may fail.

Success in communication range depends on a good antenna.The antenna should have a SWR of no more than 2 and a wave resistance of about 45-50 ohms.I am installing an antenna using a NanoWNA device.If the antenna is configured incorrectly, then not all the power will flow into the antenna.Part of the power will be released as heat on the radiator of the IRF610 transistor or radiated by a coaxial cable or the cable will start to heat up, etc.Be sure to think about it.
All power must be supplied to the antenna only! This is exactly what you need to achieve when setting up antennas with transmitters

 

My antenna is a 27 MHz dipole.These are two wires with a diameter of about 2mm and a length of 2.55 meters each.These two wires are separated in different directions and reinforced on a plastic base.The RG-58 c/u cable is connected to the antenna wires.Its wave resistance is 50 ohms.The antenna is installed vertically at a height of 10 floors.

Setting up the antenna with the transmitter.Install the high-frequency probe next to the antenna so that the probe LED emits light.Use a variable capacitor to achieve the maximum glow of the LED.This tells us that the maximum power has begun to flow into the antenna and the transmitter is configured correctly.Take the probe in your hand and it will shine brightly at a distance of even 1 meter from the antenna.

The transistor of the power amplifier will be heated by a small heatsink.The current consumption is about 1.6-1.8 Amperes with a power supply of 13.5 Volts.
Now it’s time to check the communication range.The test was carried out on a Tecsun PL600 radio receiver.At a distance of 600 meters, reception is excellent, even without an extended antenna on the receiver.Excellent reception is also at a distance of 1 kilometer, I did not go further.

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