Filter
Top Products
Theory
of
Operafon
-
4g4A/494Ap
Servlce,
Vot.
i
o
o
o
o
a
o
o
I
o
o
O
o
o
o
o
o
o
o
o
O
o
o
o
o
o
o
o
o
o
o
o
o
o
o
O
o
o
o
o
o
o
o
o
o
2ND
CONVERTER
SECTTON
(Diagram
g)
Two
2nd
ConvErter
systgms
are
used
in
the
spec_
trum
analyzer.
One
converts
207ZMHz
to
110
MHz
and
the
other
converts
g2g
MHz
to
110
MHz.
The
con_
verter
used
is
determined
by
the frequency
band
being
conveted.
The
lF
selection
for
each
banO is
snown
in
Table
7-1
along
with
the
band
frequency
range
and
the
local
oscillator
frequency
rangE.
two
2iO
lFs
are
used
by the analyzer
for
the
following
reasons:
o lf
the lst
tF
is
inctuded
in
the
frequency
band
being
converted,
it
is
possible
for
some
input
sig-
nals
to
pass
un-converted
through
the
lst
c6nvert6r
to the
2nd
Converter,
appearing
at
ttre
lst
lF.
The
resulting
spurious
signat
would
cause
the
baseline
level
on
the
screen
to rise
and
obscure
real
signat.
Two
2nd
converters
avoids
the
problem
by
usiig
a
1st
lF not
in
the
band
being
converted.
I With
two
lF'S,
lF
feedthrough
in
band
2 and
higher
order
spurs
in
bands
3 and
4lan
be eliminated.
. Because
of
the
limited
tuning
range
of
the
719MHz
LO,
the
lower
lF
cannoibe
used above
band 4.
Tabte
7-1
2ND
CONVERTER
IF
SELECTION
The
2072
MHz
2nd
Converter
mixes
the 2072MHz
from
the
1st
Converter
with
the output
trom
a
21g2
MHz
phase-locked
2nd
local oseillator.
This
local
oscillator
is swept
and
tuned over
a
4
MHz
range.
The
2A72MHz
input
tF
signal
is
passed
through
a
four-cavity
band-
pass
filt€r
(FL14)
to ailow
onty
the
2OZ2MHz
.tsi
tf
sig-
nal
to
pass
through
a1d
pr€vent
other
signals,
gei-
erated
within
the
2nd
Converter,
from getting
back
to
the
lst
Converter.
A
diode
mixer
-combines
the
2072MHz
lF input
and
the
local
oscillator
signats
to
generate
the
110MHz
lF
output
which
then
passes
through
a
110
MHz
fow-pass
fltter
to reject
any
higher
order
signals
from
the mixer.
The
829
MHz
2nd
Converter
uses
a
phase-locked
voltage
controlled
oscillator
to
produce
the
Z1g
MHz
signal
that is
mixed
with
the
g29
MHz
first
tF
signat.
The
swept
2182MHz
2nd
Local
Oscillator
is
usect
as a
reference
for
the
phase
tocked
oscillator.
The
719
MHz
oscillator
can
be
disabled
upon
command
from
the
microcomputer
in
the tF selection
process.
The
phase
lock
circuit
maintains
a constant
relationship
between
the
two local
oscillators
as
the 71
9
MHz
oscillator
is
swept
and
tuned over
a 1.33
MHz
range.
A four section
coaxial
band-pass
filter
is
used
before
the mixer
to
exclude
any
RF signals
other
than
the d€slred
g29
MHz.
Again,
a
diode
mixer
is
used
to
mix
the
g29
MHz
input
and
local
oscillator
signals
to
produce
the 110
MHz
second
lF
output.
Band
Range
2nd
LO
Range
lst
lF
1
2
3
4
5
6
7
I
I
10
11
12
50
kHz-1.8
GHz
1.7-5.5
GHz
3.0-7.1
GHz
5.4-18.0
GHz
15.0-21.0
GHz
18.0-26
GHz
26-40.0
GHz
40.0-60.0
GHz
50.0-90.0
GHz
75-140.0
GHz
110-220
GHz
170-325
GHz
2182 r.2.25MHz
719 *0.75
MHz
719 *,0.75
MHz
719
*0.75
MHz
2182
x.2.25MHz
2182 *.2.25MH?
2182 *,2.25MH2
2182 *.2.25MHa
2182
*.2.25MH2
2182 *.2.25MH2
2182 *.2.25
MHz
2182
*.2.25MH2
2072MHz
829 MHz
829 MHz
829 MHz
2072MHz
2072MHz
2072MHz
2072MHz
2O72MHz
2072MHz
2072MHz
2072MHz
7-7