# LOW FREQUENCY

Radio frequency of 30 to 300 kilohertz.

## Related Terms

### DIRECTIVITY FACTOR

1. The ratio of radiated sound intensity at a remote point on the principal axis of a loudspeaker or other transducer, to the average intensity of the sound transmitted through a sphere passing through the remote point and concentric with the transducer; the frequency must be stated.
2. The ratio of the square of the voltage produced by sound waves arriving parallel to the principal axis of a microphone or other receiving transducer, to the mean square of the voltage that would be produced if sound waves having the same frequency and mean-square pressure were arriving simultaneously from all directions with random phase; the frequency must be stated.

### POPOV'S STABILITY CRITERION

A frequency domain stability test for systems consisting of a linear component described by a transfer function preceded by a nonlinear component characterized by an input-output function), with a unity gain feedback loop surrounding the series connection.

### POLE-ZERO CONFIGURATION

A plot of the poles and zeros of a transfer function in the complex plane; used to study the stability of a system, its natural motion, its frequency response, and its transient response.

### PIEZOELECTRIC ELEMENT

A piezoelectric crystal used in an electric circuit, for example, as a transducer to convert mechanical or acoustical piezoelectric element piezoelectric gage signals to electric signals, or to control the frequency of a crystal oscillator.

### PHOTOELECTRIC CONSTANT

The ratio of the frequency of radiation causing emission of photoelectrons to the voltage corresponding to the energy absorbed by a photoelectron; equal to Planck's constant divided by the electron charge.

### PENDULUM ANEMOMETER

A pressure-plate anemometer consisting of a plate which is free to swing about a horizontal axis in its own plane above its center of gravity; the angular deflection of the plate is a function of the wind speed; this instrument is not used for station measurements because of the false reading which results when the frequency of the wind gusts and the natural frequency of the swinging plate coincide.

### PASSBAND

A frequency band in which the attenuation of a filter is essentially zero.

### PARAMETRIC EQUALIZER

[ENG ACOUS] A device that allows control over the center frequencies, bandwidths, and amplitudes (parameters) of band-pass filters that determine the frequency response of audio equipment.

### OVERTONE

One of the normal modes of vibration of a vibrating system whose frequency is greater than that of the fundamental mode.

### OPTICALLY PUMPED MAGNETOMETER

A type of magnetometer that measures total magnetic field intensity by observation of the precession frequency of magnetic atoms, usually gaseous rubidium, cesium, or helium, which are magnetized by irradiation with circularly polarized light of a suitable wavelength.

### Related questions

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