Check Frequency And Phase Measurement Accuracy - Tektronix VM700T User Manual

Appendix B: Verification Procedure

Check Frequency and Phase Measurement Accuracy

Specifications Checked
Option 40 Frequency
Accuracy and Channel
Phase Difference
B-6
b. Run the Audio Analyzer measurement and verify that residual THD+N
is 0.03% or less. An applied signal of +8 dBu to +10 dBu yields an
optimal reading, while a –20 dBu signal yields a worst-case reading.
2. Check THD+N Measurement Accuracy.
a. With 600 Ω output resistance selected, connect the outputs of two
sine-wave generators in parallel to the left channel input of the Audio
Option. See Figure B-2 for a cabling diagram.
b. Set one sine-wave generator for a 2 V
c. Set the second sine-wave generator for a 0.02 V (20 mV
These two signals add across the termination resistance to produce a
1 kHz signal with a 1% third-harmonic distortion.
d. Run the Audio Analyzer measurement and check for a THD+N reading
of 0.9% to 1.1%.
3. Move the input from the generators to the right channel and repeat step 2,
part d.
This procedure requires an accurate frequency sine-wave generator or a digital
counter to accurately set the frequency. The phase measurement requires that
both channels have the same signal applied through equal length cables.
This procedure checks the following parameters:
Frequency accuracy: 1 Hz ( or
inputs of –60 dBu or greater in the frequency range of 20 Hz to 20 kHz.
Channel phase difference: 1 for inputs of 40 Hz to 20 kHz, 2 for inputs
of 20 Hz to 40 Hz at a level of –40 dBu or greater.
1. Connect the sine-wave generator output to both the left and right inputs of
the Audio board (see Figure B-1).
2. Set the sine-wave generator for a frequency and amplitude in the specified
frequency and amplitude range of the Audio option (20 Hz to 20 kHz,
amplitude of –60 dBu or greater).
VM700T Option 40/41/42 Audio Measurements User Manual
output at 1 kHz.
RMS
0.01% + 1 digit, whichever is worse ) for
) at 3 kHz.
RMS