HP 8340A Service Manual page 131

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Fl is the PLLl IF frequency and F2 is the PLLl vco frequency.
PLLl vco frequency can be shown to be;
This shows that the PLLl vco frequency will be offset by lO*Nl
MHz from the PLL3 output frequency.
PLLl VCO operates from 200 to 300 MHz.
divided by ten to place it in the 20 to 30 MHz range.
After the final divide-by-ten, the output frequency of the 20-30
loop becomes;
from the 8340A diagnostics by pressing
the right-hand "FREQUENCY MHz" display.
"0�0000" then the PLL3/PLL1 path is not being used in this mode,
and PLL2 is used by itself. Fout, the 20-30 output frequency, can
be determined by pressing
"FREQUENCY MHz" display. Nl can be calculated from these two
frequencies using the above equation.
As the Nl divide number changes, the gain of the loop amplifier
is adjusted to maintain an approximately constant loop gain.
is done through FET switches on the A36 PLLl VCO assembly.
The PLLl vco assembly also contains an output switch to select
from one of two possible 20-30 Loop paths;
1. The PLLl VCO divided-by-ten is used as the 20-30 Output.
PLL2 is translated up through PLL3 and PLLl.
2. The PLL2 vco divided output is used directly.
are not used.
The switch positions are defined for the different 8340 operating
modes in the table in Figure 8C-6.
8-176
Model 8340A - Service
Fout (Fpll3)/10
=
[SHIFT]
Scans by HB9HCA and HB9FSX
F2 Fpll3
=
The output of the VCO is
Nl MHz. Fpll3 can be determined
+
[SHIFT] [M3]
If this display reads
[Ml] and reading the right
The
lO*Nl MHz.
+
and reading
This
PLLl and PLL3