Transmission electronics

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When transmitting electronics refers to the portion of radio systems which the power of the transmit antennas required high-frequency voltage generated.

They differ from other electronic systems with high-frequency electrical voltages in that they have a higher output power from approx. 1  watt , which is required to transmit the radio signal over greater distances using an antenna. A counter-example would be the intermediate frequency stage in radio receivers, which only generates power in the milliwatt range.

history

Pop and machine transmitters

Whereas previously only radio -, television - and amateur radio stations possessed a transmitter electronics, it is now an integral part of millions in use cellular phones (mobile phones). Electronics was not yet available at the beginning of the twentieth century. Therefore, the first radio systems used high- frequency generators , which consisted of a spark gap and a high-frequency coil. As with electrical ignition in gasoline engines , when a suitable circuit was interrupted, an electrical spark was created which, with its wide frequency spectrum up to the megahertz range, was suitable for generating a high-frequency voltage pulse. This could then be transmitted over greater distances using suitable antennas, hence the name of what is known as " broadcasting ". This meant that initially only transmissions as Morse code were possible; from the turn of the century there were also so-called machine transmitters which, for the first time, generated continuous carrier waves in the long wave range with arcs, so to speak "permanent sparks".

Tube electronics

It was only with the development of electron tubes in the middle of the first decade of the 20th century that transmission electronics emerged in the true sense of the word. Here a circuit with an active amplification element (HF tube) and strong inductive or capacitive feedback was used to generate a self-exciting oscillation. The circuit part required for this is called the oscillator. It has now become possible to radiate continuous RF carrier frequencies. The great advantage over pure spark systems is that this continuous high-frequency oscillation can be modulated, for example with voice frequency. The circuit required for this is part of the transmission electronics and is called a modulator. This modulation finds its equivalent in the receiving electronics of the receiver as demodulation, with which the pure useful signal is recovered. With the advent of electron tubes, so-called voice radio and, from the mid-1930s, even so-called picture radio , i.e. television broadcasting, became possible.

Semiconductor electronics

The output stages of normal transmission electronics in broadcasting are still partly based on electron tubes to this day, because transistors for the often required high power and high frequencies, in contrast to the transistors in radio and television receivers, are in part not yet available. The transmission electronics comprise three important circuit blocks: the oscillator , the modulator stage and the transmission stage.

In the modulator stage, the carrier frequency from the oscillator is superimposed on the useful signal to be transmitted. Different types of modulation are possible. The simplest and historically the first is amplitude modulation , in which the voltage supply of the resonant circuit varies with the cycle of the useful signal. This changes the level of the carrier frequency together with the useful signal. All you need for reception is a diode and headphones (crystal receiver). Radio transmissions with amplitude modulation are very sensitive to interference.

The next type of modulation is frequency modulation , in which the level of the carrier frequency voltage remains the same and instead the frequency of the carrier signal fluctuates in the rhythm of the useful signal. Finally, there is sideband modulation, in which the entire useful signal is contained exclusively in the frequency spectra away from the carrier frequency. With the increasing spread of transmission electronics came miniaturization. Today, the transmission electronics in mobile phones are housed in an integrated circuit together with the receiver .

literature