7. A
synthesized
subsweep is generated by
A13/A14.
The A3 source tracks
the synthesizer.
When the source
is phase locked to the synthesizer at the
start frequency, the synthesizer starts to
sweep. The
phase locked loop forces
the source to track the synthesizer,
maintaining
a constant 1
MHz
1st
IF
signal.
The full high band sweep is generated in a series of subsweeps, by phase
locking the
A3
source signal to harmonic multiples of the fractional-N VCO.
The 16 to 31 MHz subsweep is produced by a one half harmonic, using
the
divide-by-2
circuit on the
Al4
assembly. At the transitions between
subsweeps, the source is
prettmed
and then
relocks
lkble 12-3 lists the high
band
subsweep
frequencies from the fractional-N VCO and the source output.
A13/14
FRACTIONAL-N
--
TO
3GHz
ag6231d
Figure 12-5. High Band Operation of the Source
12-20
Theoryof
Operation
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