Voting indicator

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A voting indicator is an auxiliary device in radio receivers . It is used to facilitate the optimal coordination with the desired radio station in addition to the acoustic quality ( volume , distortion factor ) by means of an optical display.

The best known of older devices from the tube generation is the magic eye . The improved form is the Magic Fan .

Glow lamp serving as a tuning indicator, working like a bar graph

There were also voting displays that worked differently:

• Glow lamps with a cathode cover that can be controlled via an auxiliary electrode
• Electromagnetically driven elements that projected a shadow onto a kind of screen
• In televisions, a shadow is placed over the currently displayed television picture at the push of a button, which changes shape or expansion when properly coordinated (narrowing, bright vertical bar, downward moving bright triangle, etc.)

In newer, transistorized devices also were pointer gauges and LED - bar graphs used.

In AM receivers, the tuning display is obtained from the control signal of the automatic gain control (AGC) and thus from the rectified carrier . It therefore shows the reception field strength ; it is tuned to the maximum deflection.

In FM receivers, the tuning display signal is normally obtained from the DC component of the FM demodulator output, which enables the frequency offset (i.e. the tuning error) to be displayed directly; Here a pointer instrument with a central zero position is adjusted to zero deflection. Occasionally, however, it is also obtained from the degree of level limitation of the intermediate frequency .

Integrated circuits designed for radio reception often offer a special output for controlling a voting indicator.

Tune displays are hardly to be found today because automatic frequency adjustment (AFC) makes them unnecessary. At the beginning of the AFC they were still needed because the AFC function had to be activated manually. More modern AFCs switch themselves off automatically when the transmitter setting is activated and on again a certain time after the operation has ended. With the advent of digital tuning with the aid of quartz-stabilized PLL and DDS tuners, AFC and tuning displays finally became completely superfluous.