HP 8901B

Model 8901B Operation
Audio Detectors
FUNCTIONS
PEAK+, PEAK-, PEAKf/2, PEAK HOLD, AVG, RMS.
DESCR I PTI 0 N
The Modulation Analyzer provides three types of audio detectors: peak responding, average responding
(rms calibrated), and true rms. These three detectors provide six modes of audio measurements:
0 Positive Peak (PEAK+)
0 Negative Peak (PEAK-)
0 Average of Positive and Negative Peaks (PEAK+/P mode)
0 Positive or Negative Peak Hold (PEAK HOLD)
0 Average (AVGRMS Calibrated)
0 TmeRMS(RMS)
The two peak detector keys, when pressed individually, select whether the positive peak or the negative peak of
the demodulated signal
is measured. When the two peak detector keys are pressed simultaneously (the PEAKf/2
mode), the positive and negative peaks are averaged according
to the following equation:
(Peak+) + (Peak-)
2
Peak Average =
Peak Hold detection is used in conjunction with positive or negative audio peak detector modes. This mode enables
the instrument to hold and display indefinitely, the largest peak detected. This feature
is useful for capturing the
peak maximum
of a modulation transient.
Average detection selects an average-responding detector that is calibrated to read the rms value of a sinewave.
True RMS detection selects a true rms detector to measure audio signals. Also, noise and residual measurements
are best measured with the true
rms detector. This detector is automatically selected and is the only one used
with the external audio voltage measurement (Special Function 30), audio distortion measurement and the SINAD
measurement (Special F’unction 29). Selection of this detector also affects the FM pre-display de-emphasis. (Refer
to “COMMENTS”.)
Once selected, a detector remains unchanged and is automatically activated each time modulation measurements
are made until another detector
is selected (except for the true rms detector as discussed in the previous paragraph).
(However, once it is automatically selected, the true
rms detector remains active.)
Audio Detectors 3-173