Source Operation In Other Modes/Features - Agilent Technologies 8753ES Option 011 Service Manual

Theory of Operation

Source Operation in Other Modes/Features

Source Operation in Other Modes/Features
Besides the normal network analyzer mode, the analyzer has extra modes and features to
make additional types of measurements. The following describes the key differences in
how the analyzer operates to achieve these new measurements.
Frequency Offset
The analyzer can measure frequency-translating devices with the frequency offset feature.
The receiver operates normally. However, the source is pretuned to a different frequency by
an offset entered by the user. The device under test will translate this frequency back to
the frequency the receiver expects. Otherwise, phase locking and source operation occur as
usual.
Harmonic Analysis (Option 002)
The analyzer can measure the 2nd or 3rd harmonic of the fundamental source frequency,
on a swept or CW basis, with the harmonic analysis feature (optional).
To make this measurement, the reference frequency (normally 1 MHz) from the A12
reference assembly to the A11 phase lock assembly is divided by 1, 2, or 3. See Figure 12-6.
The fractional-N assemblies are also tuned so that the correct harmonic (comb tooth) of the
1st LO is 0.500 or 0.333 MHz below the source frequency instead of the usual 1.000 MHz.
The analyzer pretunes the A3 source normally, then phase locks the 1st IF to the new
reference frequency to sweep the fundamental source frequency in the usual way. The key
difference is that the 1st IF (output from the R sampler) due to the fundamental and used
for phase locking is now 0.500 or 0.333 MHz instead of 1.000 MHz.
Since the chosen VCO harmonic and the source differ by 0.500 or 0.333 MHz, then another
VCO harmonic, 2 or 3 times higher in frequency, will be exactly 1.000 MHz away from the
2nd or 3rd harmonic of the source frequency. The samplers, then, will also down-convert
these harmonics to yield the desired components in the 1st IF at 1.000 MHz. Narrow
bandpass filters in the receiver eliminate all but the 1.000 MHz signals; these pass
through to be processed and displayed.
12-22 Chapter 12