HP 8340A Service Manual page 117

INTRODUCTION
The 20-30 Loop consists of the following assemblies:
A36 PLLl VCO
A37 PLLl DIVIDER
A38 PLLl IF
A39 PLL3 UP CONVERTER
A40 PLL2 VCO
A41 PLL2 PHASE DETECTOR
A42 PLL2 DIVIDER
A43 PLL2 DISCRIMINATOR
DESCRIPTION
The 20-30 Loop provides the 8340A with 1 Hz CW
resolution. In swept frequency modes the 20-30 Loop provides high
resolution tuning in sweep widths from 100 Hz to
In sweep widths less than 5 MHz,
during the sweep,
For sweep widths greater than
and the YO is swept
These assemblies form a frequency synthesizer with the following
performance characteristics:
Fixed frequency output range from 20 to 30 MHz
�
Analog sweep widths between 100 Hz and
�
CW frequency resolution as low as 1 Hz
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The 20-30 Loop contains three phase locked loops that are used in
three different configurations to achieve the required CW
resolution and sweep range.
PLL2 and PLL3. PLL2 is always used in the 8340A,
the instr ument's mode of operation.
be phase-locked to the output of PLL2,
to PLL2.
Figure 8C-l,
Diagram,
configurations mentioned below.
Model 8340A - Service
20-30 LOOP
OVERALL DESCRIPTION
the YO Loop remains phase-loc�ed
and the 20-30 Loop is swept the desired amount.
5 MHz,
(lock and roll sweep)
The loops are referred to as P�Ll,
NOTE:
20-30 Loop Simplified Block
illustrates the three
Scans by HB9HCA and HB9FSX
(YO)
5 MHz.
the 20-30 Loop remains fixed
•
5 MHz
regardless of
PLLl and PLL3 are arranged to
and can sweep while locked
tuning
8-161