In this article I will tell in detail how to make a telegraph transmitter, with which you can conduct radio communication in Morse code on short waves at a distance of at least 2500 kilometers, I covered this distance under my conditions and in my case being in the city and living on the 10th floor. I received my signal on a web-sdr receiver, which is located in the city , to which the distance in a straight line is 2500 kilometers. The output power of the transmitter is about 1.2 W, the output stage is assembled according to class E on a BS170 transistor
The master oscillator is assembled on the SN74HC74 dual D-trigger microcircuit and is powered by 5 volts from the 78L05 microcircuit. The transmitter frequency is set by a quartz resonator at a frequency of 14 MHz with something kilohertz. I installed the quartz that I had available at a frequency of 14.318 kHz. At pin 9 of the microcircuit there will be a rectangular signal with a frequency half that of the quartz resonator. The main thing is that this frequency falls on the frequencies where radio communications are conducted by telegraph. There must be a rectangle at the generator output. If there is a sawtooth or a constant signal in general, and this can be due to a bad quartz, then the BS170 transistor will begin to heat up strongly or even fail immediately after switching on. Check the operation of the generator by turning it on and off, the signal at the output should always be stable. The signal from the generator goes to the output stage, assembled on the BS170 transistor. This field-effect transistor has a small input capacitance of 24-40 pF, this capacitance is fully charged and discharged by the microcircuit and the capacitance is not an obstacle. If you install a transistor, say, IRF510 with a much larger input capacitance, then the microcircuit will work poorly with such a capacitance and the output power will be small. Since the BS170 transistor works with a pulse signal, it does not require a heat sink. Such an output stage in transmitters, where the transistor works as a key, is called class E. A rectangular signal is converted into a sine wave using the L2 coil and the C6 capacitor. The 8550 transistor works as an on-off switch for the transmitter and is controlled by a key that beats out Morse code. Coil L1 is a 4.7 μH choke. Coil L2 is wound on a 17 mm diameter frame and contains 20 turns of 0.6 mm diameter wire
Now the setup. I measure the power and frequency of the signal using a GY561 device that has a resistor. I look at the waveform on an oscilloscope. If you don't have any of this, then prepare a non-inductive resistor with a resistance of 47 Ohms and a power of 2 W or more, if you have a 50 Ohm one, then this one will do. Connect a 50 Ohm coaxial cable about 50 cm long to the transmitter output, parallel to capacitor C6, but not the one in my photo, it has too much signal attenuation. I will tell you about coaxials in another article, which of them are normal and which are not. Connect a 47 Ohm resistor to the cable output. Set the supply voltage to 8 Volts and connect the power plus to the choke L1, bypassing the 8550 transistor. Instead of capacitor C6, install a variable capacitor and by changing its capacitance, find the maximum output power. Measure the capacitance of the variable capacitor and install constant. If you do not have devices, then connect a diode and a capacitor to the resistor according to the circuit of a half-wave rectifier and a voltmeter to it. The higher the voltage the voltmeter shows, the higher the output power. You can simply navigate by the heating of the resistor. If a 2 W resistor heats up, then everything is ok
We increase the power supply to about 14-15 volts and check that the BS170 transistor is not hot and that everything works and does not fail. Above 16-17 volts of power supply, the transistor in my case could fail.With a power supply of 13 volts and a current consumption of 90 mA, the output power of the radio transmitter will be 800 mW.With a power supply of 16 volts and a current consumption of 100 mA, the output power of the radio transmitter will be 1.2 W.
The antenna was used by Fuchs. This is a wire about 40 meters long, going down from the 10th floor to the first at an angle. The wire is connected to the matching device and a coaxial cable coming from the transmitter is connected to it. When connecting the antenna, the transmitter power supply must be set to 8 volts. After tuning the antenna to resonance, we increase the power supply to 12-13 volts, while you need to look at the current consumed by the transmitter. If the current is 90-100 mA, try to increase the supply voltage even more. It is desirable that you have several BS170. Burn one transistor during tuning by increasing the supply voltage to the maximum. This way you will know where the power supply limit will be. After all, the higher the supply voltage, the greater the output power of the transmitter
The high-frequency radiation from the antenna can be detected using a high-frequency probe with two diodes and a light-emitting diode. It was very unusual and surprising to hear myself at such a large distance with such low power. Moreover, I cover such a distance almost every night
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