M/N Loop Theory Of Operation; M/N Loop Theory Of Operation; A32 M/N Vco Assembly; A33 Output Assembly - HP 8340B Manual

M/N
Loop
Theory of Operation
The M/N loop generates the 177-197
MHz
signal
that drives the
A48 sampler
in the
YIG
oscillator (YO)
phase
lock feedback loop.
The M/N loop uses the 20 and
400 MHz reference
signals from the
reference
loop.
The A48 sampler down-converts the output of the YIG oscillator so the YO
can be phase locked to the
output of the 20-30
loop.
The M/N
loop consists of four assemblies, shown in
functional order below:
•
A32 M/N VCO
assembly
•
ASS M/N output
assembly
•
A31 M/N
phase detector assembly
•
A34 reference loop
—
M/N
loop motherboard
The
YO
loop
sampler drive output of the
M/N loop (after being divided by 2) can be related to the M
and
N numbers by the following equation:
fM/N
=
200
-
10
X
(M/N) MHz
A
harmonic of
this signal
is
used
in
the A48 YO
loop
sampler to down-convert the 2.3 to 7.0 GHz YO
output to 20 to 30 MHz.
For every increment
in M number, the YO output decreases by 10
MHz,
and for
every increment
in N
number, the
YO output increases by 200 MHz. This
relationship
is
given
in the
following
equation where
^0,30 is
the output of the 20 to 30 Loop:
fyo =
200XN
-
10XM
-
f2o,3o
MHz
A32 M/N VCO ASSEMBLY
The M/N VCO
is
a
cavity resonator that
is
varactor tuned from 355
to
395 MHz. The VCO
output goes
to the A33 M/N
output assembly
A33 OUTPUT ASSEMBLY
The VCO output
is
split by the A33 output assembly and sent to two
circuits:
•
The A48 YIG oscillator sampler assembly. This is
the output of the entire
M/N
loop, and is divided
by two before going to the
YO
sampler.
•
The
A31 phase
detector, where the
VCO
output
is
phase-locked to
the 400 MHz
reference loop
output.
The M/N VCO
assembly
is
mounted to the A33 M/N
output assembly.
B-4
M/N
Loop Theory of Operation
HP 8340B/41B