The Model 339A Distortion Measurement Set combines a low distortion signal source, a high resolution distortion analyzer, an rms responding voltmeter and a VU (volume units) meter in one unit.
The signal source used in the Model 339A is a "bridged-T" oscillator which provides a low distortion sine-wave signal from 10 Hz to 110 kHz. The output amplitude is variable from 1 mV rms to 3 V rms into a 600 ohm load and is maintained by an amplitude control circuit which minimizes amplitude variations even when changing frequency ranges.
The distortion analyzer section of the 339A contains a tracking notch filter which is tuned to the oscillator frequency. The analyzer measures total harmonic distortion (THD) from 100% full-scale to .01% full-scale in nine ranges and features both automatic "Set Level" and automatic "Nulling" to greatly simplify operation. The Auto Set Level feature automatically sets the reference level over a 10 dB range. If the input signal is outside this range, a LED on the front panel indicates whether the INPUT RANGE control setting must be increased or decreased to be within the "pull-in" range of the Auto Set Level.
The Auto Nulling feature is fully automatic when the 339A internal oscillator is used as the signal source. When an external oscillator is used as the signal source, an LED on the front panel indicates which direction the FREQUENCY controls must be set to be within the Auto Nulling range. Distortion characteristics of the input signal can be monitored at the MONITOR OUTPUT terminals with external equipment (oscilloscope, voltmeter, spectrum analyzer, etc.) to provide additional analysis of the distortion products.
The Model 339A is equippped with an amplitude modulation (AM) detector which has a frequency response from 550 kHz to 1.6 MHz. The AM detector permits the measurement of modulation distortion.
The 339A contains three active filters, one high-pass and two low-pass, which enables the user to eliminate unwanted frequencies and noise to permit higher resolution measurements.
The ac voltmeter section of the 339A measures the rms value of input voltage from 1 mV full-scale to 300 V full-scale in twelve ranges. In the VU meter mode, the meter response characteristics are changed to those of a volume units meter.
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