Transmitter on the LM317 chip. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Transmitters
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A few years ago, I put together one of my designs that didn't work as it should and produced something strange. The power supply for a portable radio receiver generated high-frequency vibrations! The error was due to incorrect connections on the PCB. After a little investigation, I applied the obtained effect to build a CW QRP transmitter, the heart of which was the integrated voltage regulator LM317T (K142EN12).
The above diagram needs little to no explanation. It operates at a supply voltage of 10 volts and produces a stable voltage of 4,5 volts. LM317 is used as an active element of the RF generator, the frequency depends on the parameters of the VC1 / L1 circuit. The first tap is made from 3% of the total number of turns L1. The second tap is made from 6% of the total number of turns and is connected to the LM317 control terminal, the output to the antenna is made from 12% of the turns of the same coil, the power supplied to the antenna can be several watts.
I do not see any obstacles to increase the power of this transmitter, especially since I myself have tested it on the 1,8 MHz band and made several CW QSOs. It is also possible to use this design on the new 70kHz band, but I don't know how effective it will work. I have just quoted from my workbook and leave open the possibility for all sorts of experiments.
The starting point for circuit calculations VC1 / L1, L1 is the usual formula: the number of turns is numerically equal to the wavelength in meters and the maximum value of VC1 in picofarads (must be multiplied by 2, since this is a variable capacitor).
Author: Harry Lythall (SM0VPO)
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