Chapter 2 47
Operation
Using the Mixers with the 8566B Spectrum Analyzer
Operation
Signal Identification
Figure 2-18 shows a typical full-band display of a single input signal. Direct interpretation
of the display is difficult because of the large number of responses produced by several
local oscillator harmonics generated in the mixer. To solve this problem the 8566B
spectrum analyzer uses two methods of signal identification.
The first is an automatic image search in which the spectrum analyzer looks for a signal
image within a preset range of harmonic numbers. This automatic signal identification
routine is initiated by pressing SHIFT, 3, MHz. Upon completion, one of three messages
appears on the CRT: SIGNAL NOT IDENTIFIED, SIGNAL IDENTIFIED OUT OF BAND (with
the frequency), or CENTER (with the identified signal frequency). The range of harmonic
numbers through which the spectrum analyzer searches can be changed by accessing
“search start HN” and “search stop HN,” which are SHIFT, 7, MHz and SHIFT, 8, MHz,
respectively.
The second method, manual signal identification, is a fast method of verifying that the
displayed signal is a true signal in the specified band. Press SHIFT, 4, MHz to activate this
function. Positive signal identification is indicated if the signal in question does not change
frequency and is reduced in amplitude by one to two divisions on alternate sweeps. A failed
signal identification is indicated by the signal disappearing or shifting in frequency.