What was the very first homemade radio receiver that an amateur radio operator had a few decades ago? That’s right-detector.There is no simpler radio receiver than this, just one diode, an oscillating circuit and a capacitor and the receiver is ready.It does not need a power source, it is powered by the energy of radio waves that comes from the antenna.The operation of the receiver depends entirely on its size and quality.The higher the antenna is raised from the ground, the better reception, and the antenna dimensions should be normal.In my case, this is a 15-meter-long wire dropped from a balcony from a height of 10 floors only for the night, since soon this wire may not be seen, it will be cut off by neighbors.The receiver needs grounding, I have this role performs a central heating battery.The diode needs germanium, type D9, D2, D18, etc.At night, on this receiver in 2021, I received three radio stations.The inductance coil I had was wound on a frame with a diameter of 20mm and contained 15 turns with a ferrite rod of 400 NN, coils for medium and long waves will no longer give reception.With a variable capacitance capacitor, I regulate the connection with the antenna in order to somehow separate the radio stations from each other, otherwise there will be two or three radio stations receiving at the same time.This is the disadvantage of this receiver, too poor selectivity.I also performed tuning or tuning ferrite rod.
And now check the operation of this receiver.Since the receiver is a receiver of amplitude-modulated signals and the diode is a demodulator of these signals, I have assembled an analog radio station-a transmitter of amplitude-modulated signals on one transistor.This is an imitation of a radio station signal.
Without sound on the transmitter, that is, without modulation, the signal at the output of the transmitter will be a stable sine wave.Now I turn on the player and on the oscilloscope screen we will see that the tip of the sine wave will begin to oscillate up and down in time with the sound, this is amplitude modulation.
Now I connected a detector receiver-a diode and a 4700 pF capacitor to the output of the transmitter, and connected an oscilloscope to the output of the receiver.Now you can see that when the transmitter is not modulated, there will be silence at the receiver output and we will see a straight line on the screen.When the sound is applied to the transmitter, we will see a sound signal on the screen.A diode with a capacitor was “pulled” from a high-frequency signal by a sound signal, and the high-frequency signal was extinguished.
Result.This receiver is still working today, but there is almost no broadcasting of powerful radio stations on long and medium waves, so the receiver probably won’t work on these bands anymore.Radio China and other radio stations are broadcasting on short waves today, and my receiver was tuned to these waves.But I live in Siberia and the signals are powerful here.
