
Source
Super
Lo
w
Band
Operation
The
Sup er
Lo
w
Band
F
requency
Range
is
10
kHz
to
300
kHz.
These
frequencies
are
generated
b
y
the
A12
Reference
Board.
They
are
the
amplied
output
of
the
fractional-N
syn
thesizer.
This
output
is
not
phase
lo
c
k
ed
and
is
not
sub
ject
to
ALC
con
trol.
Refer
to
T
able
12-1.
T
able
12-1.
Super
Lo
w
Band
Subsw
eep
Frequencies
F
ractional-N
(MHz)
1st
IF
(MHz)
RF
Output
(MHz)
40.0
to
43.3
0.010
to
0.300
0.010
to
0.300
Source
Lo
w
Band
Operation
The
low
band
frequency
range
is
300
kHz
to
16
MHz.
These
frequencies
are
generated
b
y
lo
c
king
the
A3
source
to
a
reference
signal.
The
reference
signal
is
syn
thesized
b
y
mixing
do
wn
the
fundamen
tal
output
of
the
fractional-N
V
CO
with
a
40
MHz
crystal
reference
signal.
Lo
w
band
op eration
diers
from
high
band
in
these
resp ects:
The
reference
frequency
for
the
A11
phase
lo
c
k
is
not
a
xed
1
MHz
signal,
but
v
aries
with
the
frequency
of
the
fractional-N
V
CO
signal.
The
sampler
dio
des
are
biased
on
to
pass
the
signal
through
to
the
mixer.
The
1st
IF
signal
from
the
A4
sampler
is
not
xed
but
is
iden
tical
to
the
RF
output
signal
from
the
A3
source
and
sw
eeps
with
it.
The
following
steps
outline
the
low
band
sw
eep
sequence,
illustrated
in
Figure
12-4.
1.
A
signal
(FN
LO)
is
generated
b
y
the
fractional-N
V
CO.
The
V
CO
in
the
A14
F
ractional-N
assem
bly
generates
a
CW
or
sw
ept
signal
that
is
4O
MHz
greater
than
the
start
frequency
.
The
signal
is
divided
do
wn
to
1OO
kHz
and
phase
lo
c
k
ed
in
the
A13
assem
bly
,
as
in
high
band
op eration.
2.
The
fractional-N
V
CO
signal
is
mixed
with
40
MHz
to
pro duce
a
reference
signal.
The
signal
(FN
LO)
from
the
F
ractional-N
V
CO
go
es
to
the
A12
reference
assem
bly
,
where
it
is
mixed
with
the
4O
MHz
V
CX
O
(v
oltage
con
trolled
crystal
oscillator).
The
resulting
signal
is
the
reference
to
the
phase
comparator
in
the
A11
assem
bly
.
3.
The
A3
source
is
pretuned.
The
signal
(RF
OUT)
is
fed
to
the
A4
sampler.
The
pretuned
D
A
C
in
the
A11
phase
lo
c
k
assem
bly
sets
the
A3
source
to
a
frequency
1
to
6
MHz
ab o
v
e
the
start
frequency
.
This
signal
(RF
OUT)
go
es
to
the
A4
R
input
sampler/mixer
assem
bly
.
(The
source
RF
output
must
b e
connected
externally
to
the
R
input
connector
in
the
Option
011.)
4.
The
signal
from
the
source
is
fed
bac
k
(1st
IF)
to
the
phase
comparator.
The
source
RF
OUT
signal
passes
directly
through
the
sampler
in
the
A4
assem
bly
,
b ecause
the
sampler
is
biased
on.
The
signal
(1st
IF)
is
fed
bac
k
unaltered
to
the
phase
comparator
in
the
A11
phase
lo
c
k
assem
bly
.
The
other
input
to
the
phase
comparator
is
the
hetero dyned
reference
signal
from
the
A12
assem
bly
.
An
y
frequency
dierence
b et
w
een
these
t
w
o
signals
pro duces
a
prop ortional
error
v
oltage.
5.
A
tuning
signal
(YO
DRIVE)
tunes
the
source
and
phase
lo
c
k
is
ac
hiev
ed.
The
error
v
oltage
is
used
to
driv
e
the
A3
source
YIG
oscillator
to
bring
the
YIG
closer
to
the
reference
frequency
.
The
lo
op
pro cess
con
tinues
un
til
the
source
frequency
and
the
reference
frequency
are
the
same,
and
phase
lo
c
k
is
ac
hiev
ed.
DRAFT
3/21/106
15:14
Theory
of
Operation
12-11
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