Tektronix 2714 User Manual page 150

Enhanced Versatility
MAX HOLD A&B
The A and B registers can be used in the MAX HOLD mode to save the
peak values of measured spectra. The register must be cleared before
you can use it in the MAX HOLD mode.
The MAX HOLD feature compares the amplitude of the current sweep,
point for point, with the stored maximum value of previous sweeps. If
the current amplitude is greater, the current value becomes the new
stored maximum; if not, the previous value is retained.
Deactivate the D register. Make sure the A register is cleared and
activated, then press [MAX HOLD A & B].
The red LED below the MAX HOLD A & B key lights signifying that
you have entered the MAX HOLD mode. The spectral display, espe-
cially the noise, is much smoother. After several minutes, the noise
floor appears to drift upwards a couple of dB. Because the calibration
signal is constant, there is no noticeable change in it. The upward drift
of the noise floor slows and stops as the most likely maximum values
are observed and stored. Now only an occasional noise peak exceeds
the previously stored values. Activate the D register. Note that the
waveform in the D register (waveform without MAX HOLD) is always
less than the A register waveform. Recording the peak signal excur-
sions observed during a large number of sweeps using the MAX
HOLD feature yields an estimate of the maximum signal values. It can
also be very useful for determining maximum signal amplitude during
transient conditions or for making low-level fluctuating signals more
apparent by saving their peak value. You can observe as many
sweeps as you wish. You could equally as well have used the B
register for MAX HOLD.
When you are ready to exit the MAX HOLD mode, press [MAX HOLD
A & B] to turn off the A register. The red LED goes out, and only the D
register sweep remains.
A feature called MIN HOLD, similar to MAX HOLD and activated by
pressing [DSPL] [9], saves the minimum signal values. Using both
MIN HOLD and MAX HOLD, you can measure a signal's total excur-
sion.
2714 User Manual 5-31