HP 3562A Operating Manual page 64

THE AUTO CORRELATION MEASUREMENT
THE AUTO CORRELATION MEASUREMENT
The auto correlation measurement indicates periodicity in time domain signals. It multiplies the
signal by a progressively time-shifted version of itself; this emphasizes periodic parts of the
signal and de-emphasizes non-periodic parts. In the HP 3562A it is computed using the
inverse FFT of the power spectrum:
To avoid wrap-around error, both correlation measurements discard the last half of the time
record. The measurement display is therefore half the length of the time record. If some signal
of interest is present in the last half of the record, use delayed triggering to move the deleted
portion of the record.
Some uses of auto correlation are detecting periodicity and measuring impulsive signals, such
as gear chatteL Auto correlation is especially useful for extracting a periodic signal buried in
noise when a synchronized trigger is not available. To select this measurement, press SELECT
MEAS, followed by the AUTO CORR softkey.
To select a display for the auto correlation measurement, press MEAS DISP to display the
following menu:
1-10
Chapter i-Using the Linear Resolution Mode
where: Gxx is the power spectrum
AUTO
Displays the auto correlation of the signal on Channel 1
CORR1
(This soflkey appears if Channel 1 is active.)
AUTO
Displays the auto correlation of the signal on Channel 2.
CORR2
(This soflkey appears if Channel 2 is active.)
AUTO
Displays the trace calculated with the auto math table: see
MATH "Auto Math" in Chapter 9. Note that this softkey label
might be replaced by a user-defined label.
FILTRD
Displays the filtered input menu, which provides time
INPUT
record and linear spectrum displays; see "Filtered Input
Displays" later in this chapter.
.