Overall Instrument Theory; Overall Instrument Theory; Reference Loops; M/Nloop - HP 8340B Manual

HP
8340B/41B Assembly-Level
Service
Overall Instrument Theory
The HP
8340B
is
a
synthesized
sweeper
that covers the frequency range from
10
MHz
to 26.5 GHz,
in
five bands.
The
HP 8341B
is
a
synthesized
sweeper
that covers the frequency range from
10 MHz
to 20.0
GHz,
in
four
bands.
The
instrument bands are:
•
Band
0
10
MHz
to
2.3 GHz
•
Band
1
2.3 to 7.0 GHz
•
Band
2
7.0 to
13.5
GHz
•
Band
3
13.5 to 20.0
GHz
•
Band
4
20.0
to
26.5 GHz (HP 8340B only)
Internal to the instrument are
7
phase-lock loops,
17 high frequency microcircuits, and
a
16-bit
micro¬
processor.
REFERENCE LOOPS
Frequency accuracy and stability are tied to either the 10 MHz
internal frequency standard or
an
external
5 orlO MHz source. The reference loop uses this 10 MHz
to generate
all of the translation and
reference signals used by other phase-lock loops
in the instrument. These
signals are:
•
400
MHz
and 20
MHz
signals used
in the
M/N
loop to
produce the
M/N
output
frequency.
•
10
MHz
and 100
MHz
signals used as reference signals
in the
20-30
loops.
•
A
separate, lower
power
100
MHz
output sent
to the RF section
to phase lock the
3.7 GHz
oscillator to the 10
MHz
reference.
M/N LOOP
The M/N
loop produces an output between 177 and 197
MHz that drives
a
sampler
in
the
YO
loop.
The
variables
M
and
N
are
integers generated by the processor, and control the output frequency of the
M/N
loop.
The output from the sampler
in the
YO
loop
must always be between 20 and 30
MHz
to be
compared
and phase locked to the output of the 20-30 phase lock loops.
With the YO
at
a
specific
frequency between 2.3
and 7.0 GHz, there
is
an
M/N
output frequency
between 177 and 197
MHz. When
a
harmonic of this
frequency
is
mixed with the YO frequency
in
the
sampler, an
IF output between 20 and 30 MHz
results.
The
sampler output
is then
compared
to the
20-30
loop output by the YO loop phase/frequency detector
in
the YO loop.
A-4
Assembly-Level Service Overall Instrument Theory
HP 8340B/41B