Heterodyne Resonance Indicator

Heterodyne Resonance Indicator


a measuring instrument for tuning high-frequency circuits in radio receivers and transmitters in the frequency range from 100 kilohertz (kHz) to 90 megahertz (MHz), which is used mainly by radio operators. A heterodyne resonance indicator (see Figure 1) consists of a generator with self-excitation (a heterodyne), a pointer indicator (for example, a microammeter), and a receiver. The indicator is tuned to the required frequency by a condenser, which is equipped with a readout scale for the sake of convenience. The operating frequency range is changed by changing inductance coils.

Figure 1. Schematic diagram of a heterodyne resonance indicator: (ET) electron tube, (Cc) tuning condenser, (Lc) circuit inductance, (M) microammeter, (D) detector, (R) receiver, (Cb) blocking capacitor (E) excitation circuit switch

The heterodyne resonance indicator operation is based on the fact that when two oscillator circuits are tuned to resonance, a maximum energy transfer from one circuit (the heterodyne resonance indicator) to the other circuit (the circuit under investigation) takes place. Depending on the mode of operation of the indicator, the device may be utilized as a resonance or heterodyne frequency meter. In the former case, the power supply of the indicator is turned off. The indicator is tuned to the frequency of the transmitter under test, which is determined from the indicator scale at the moment of maximum deflection of the indicator needle. In the latter case, the transmitter frequency is determined by the zero-beat method, and the power supply of the indicator is not turned off. The error of measurements by this method does not exceed ± 15-20 Hz (the audible frequency threshold), but the measurement sensitivity is considerably higher than in the first case.

In some heterodyne resonance circuits, the high-frequency oscillations are modulated by low frequency. Frequently the heterodyne frequency indicators are of transistorized or mixed design (with ampere-volt-ohmmeters and other electrical measuring instruments).


Sokolov, V. “GIR na tranzistore.” Radio, 1966, no. 12.
Lomanovich, V. “Kombinirovannyi GIR.” Radio, 1967, no. 9.


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