Ramsey Electronics COM 3 User Manual

5.1 GENERAL
The
Com
3
is
composed
basically
of
three
phase
locked
loops,
whose
outputs
are
combined
through
various
mixers
and
amplifiers
to
give
a
final
output
frequency
range
of
100
KHz
to
999.9999
MHz
in
500
Hz
steps.
The
main
VCO
or
PLL
tunes
from
506
MHz
to
1017
Mhz
in
2
MHz
steps,
we'll
Call
that
loop
the
coarse
loop,
since
its
frequency
Steps
coarsely
tune
the
service
monitor's
RFgenerator.
The
fine
loop,
which
tunes
in
500
Hz
Steps,
runs
from
5
Mhz
to
7
Mhz.
The
output
of
the
fine
loop
is
mixed
with
the
506
to
1017
Mhz
loop
in
mixer
X2,
which
produces
an
output
of
505
to
,
1011
Mhz
in
500
Hz
steps.
The
coarse
loop
steps
'
every
2
Mhz
and
the
5
to
7
Mhz
loop,
which
has
a
tuning
range
of
2
Mhz,
mixes
with
the
coarse
loop
to
give
the
finer
resolution
Steps
across
the
entire
band.
Using
general
numbers
we
see
that
one
loop
tunes
from
500
to
1000
Mhz
in
2
Mhz
steps,
and
the
other
loop
tunes
from
5
to
7
MHz
in
500
Hz
steps.
To
obtain
0
to
500
Mhz
from
the
Com
3,
the
output
of
the
coarse
loop
is
mixed
with
another
oscillator
that
runs
at
about
1000
MHz
(
actually
1024
Mhz).
Taking
the
500
to
1000
MHz
.
SECTION
5
THEORY
OF
OPERATION
subtracted
from
1000
you
will
see
that
the
result
is
0
to
500
MHz.
,
Of
the
three
loops,
the
fine
loop,
and
the
coarse
loop
run
continually,
and
the
offset
oscillator
or
loop
(1024
MHz)
is
only
switched
in
for
the
lower
band
of
0
to
500
MHz.
The
final
output
of
allthese
PLLs
is
the
channel
frequency.
Some
form
of
attenuation
is
required
to
give
a
variable
range
from
0.1
uv
to
10,000
w.
This
attenuation
is
performed
in
two
sections,
one
being
a
continously
variable
20
dB,
and
the
other
a
Switchable
step,
0-80
dB.
The
variable
attenuator
is
part
of
the
AM
modulator
section
and
uses
a
double
balanced
modulator
IC.
Its
output,
variable
over
a
20
dB
range,
is
then
applied
to
the
step
`
attenuator.The
step
attenuator
is
controlled
in
20
dB
steps
utilizing
pin
diodes
.
The
signal
is
then
directed
to
the
output
jack.
In
the
receive
mode
the
same
PLLs
are
utilized.
However,
the
input
frequency
of
100
KHz
to
999.9999
MHz
is
applied
to
mixer
X3,
and
mixed
with
the
output
of
the
coarse
loop
(
506
to
1017
Mhz
in
2
MHz
steps).
This
will
allow
the
Com
3
to
receive
frequencies
from
505
-999.9999
MHz.
For
EA
AA
AA
መር
~

Ramsey Electronics COM 3 Specifications

General

Brand	Ramsey Electronics
Model	COM 3
Category	Monitor
Language	English