HP 8901B Operation And Calibration Manual page 294

Model
8901B
Operation
Audio Frequency
FUNCTIONS
AUDIO FREQ, AUDIO INPUT
DESCRIPTION
Audio Frequency counting can be performed on either demodulated internal signals or external audio
signals as determined by the AUDIO INPUT key.
PROCEDURE
To count the frequency of the audio signal demodulated from the
FtF
signal at the INPUT connector,
select AUDIO FREQ (Shift, AM).
To count the frequency of an external audio signal at the MODULATION OUTPUT/AUDIO INPUT
connector, follow the above procedure, and then select AUDIO INPUT. The measurement range is
20
Hz to
250
kHz. The input signal should not exceed
4
Vrms. The input impedance is approximately
100 kn.
HP-IB PROGRAM CODES
AUDIO FREQ
=
S1
AUDIO INPUT
=
A1
MEASUREMENT TECHNIQUE
The audio frequency is measured by a reciprocal-type counter. The input can be either the demodulated
FtF
at the INPUT or an external audio input at the MODULATION OUTPUT/AUDIO INPUT. The
Modulation Analyzer gates its internal 10 MHz time base reference with the audio input signal for at
least 100 ms. The frequency is then determined
by
the following equation:
(number of cycles of audio signal) x 10
M H z
number of time base reference pulses
audio frequency =
The combination of minimum count time of 100 ms and the 10
MHz
time base reference assures
six-digit resolution.
Audio Frequency 3-199