Ramsey Electronics COM 3 User Manual

the
lower
band
of
0.1
to
505
Mhz,
the
coárse
loop
(506-1017
MHz)
signal
is
mixed
with
the
offset
loop
(1024
MHz)
at
mixer
X5.
This
output
is
then
mixed
with
the
incoming
signal
at
mixer
X3.
This
allows
reception
of
signals
from
0.1
-505
MHz.
When
the
service
monitor
is
in
the
receive
mode,
the
microprocessor
directs
the
synthesizers
to
output
a
frequency
which
is
9.5
MHz
higher
than
what
is
desired
to
be
received,
therefore
we
use
a
9.5
Mhz
IF.
The
RF
input
to
the
first
mixer,
X3,
is
combined
with
the
output
of
the
coarse
loop.
This
produces
an
output
of
14.5
to
16.5
MHz.
This
output
is
bandpass
filtered,
then
amplified
by
a
low
noise
microwave
transistor
which
sets
the
noise
figure,
and
thus,
the
sensitivity
of
the
service
monitor.
The
output
of
this
low
noise
amplifier
is
directed
into
an
additional
mixer
X4
where
it
is
output
is
then
sent
through
a
2
pole
bandpass
filter
before
arriving
at
the
AM
and
FM
receiver
portion
of
the
service
montior.
All
these
individual
circuits
will
be
discussed
in
detail
in
the
following
sections.
5.2
506-1017
MHz
COARSE
LOOP
PLL
The
Coarse
Loop
tunes
from
506
-
1017
MHz
in
2
MHz
steps.
The
coarse
loop
uses
what
is
known
as
dual-modulus.
prescaling
,
using
a
varable
division
divider.
If
you
notice
on
the
circuit
diagram
you
see
that
U13
is
a
divide
by
10
or
divide
by
11.
The
division
ratio
can
be
controlled
by
the
synthesizer
chip.
The
reason
dual-modulus
is
used,
is
that
it
makes
it
appear
to
ihe
phase
detector
that
a
much
higher
reference
frequency
is
used
.
The
higher
the
reference
frequency,
the
faster
the
loop
will
respond,
and
the
cleaner
the
loop
will
be.
The
synthesizer
IC
used,
U14,
is
a
Motorola
MC145156P1.
The
MC145156P1,
receives
its
division
instructions
from
the
microprocessor
by
way
of
three
lines.
The
three
lines
are;
clock,
data,
and
enable.
The
clock
and
data
signals
are
ignored
by
the
MC145156P1
except
for
when
the
enable
input
is
high.
When
this
happens,
the
synthesizer
looks
at
the
data
and
controls
the
programable
dividers
accordingly.
Also,
internal
to
the
MC145156P1,
is
a
reference
divider.
Since
the
input
frequency
to
the
-
combined
wth
the
output
of
the
fine
loop
5:57
MHz).
The
final
output
of
mixer
X4
is
at
9.5
MHz.
This
5
2
MC145156P1
is
4
MHz,
and
the
reference
.
frequency
desired
is
500
KHz,
the
reference
divider
is
preset
inside
the
MC145156P1
to
divide
by
8.
The
phase
detector
outputs
of
the
MC145156P1
appear
on
pins
4
and
3.
The
outputs
are
a
charge
up
and
a
charge
down,
which
are
used
to
control
the
loop
filter
which
is
composed
of
U16
and
its
associated
components.
U16
also
performs
the
function
of
a
level
shifter.
U14
(MC145156P1)
runs
on
6.2
volts,
and
the
VCO
requires
a
tuning
range
of
1.5
to
27
volts,
therefore
U16
runs
on
a
30
volt
supply
and
also
has
the
proper
amount
of
gain
to
shift
the
6.2
volt
level
from
the
MC145156P1
up
to
the
1.5
to
27
volt
level
required
by
the
VCO.
The
VCO
consists
of
transistor
Q5
,
along
with
varactor
diodes
D21,
D22,
D23.
The
oscillator
is
very
unique
in
that
it
will
tune
approximately
one
octave.
In
order
to
tune
the
oscillator
over
one
octave,
variable
feedback
must
be
used.
Most
VCOs
use
just
a
pair
of
diodes
in
the
tuned
circuit,
however
this
VCO
uses
an
additional
diode
which
comes
off
the
emitter
of
the
VCO
transistor
.
This
varactor
diode,
provides
the
effect
of
bypassing
the
emitter
more
at
the
lower
end
of
the
tuning
range,
and
at
the
higher
end
of
the
tuning
range
leaving
the
emitter
floating
above
ground.
;
To
provide
stability
of
the
VCO
over
the
entire
tuning
range,
a
constant
current
bias
source
is
used,
which
keeps
the
emitter
current
constant
throughout
the
entire
tuning
range.
That
circuitry
is
composed
of
transistor
09,
894,
R95,
and
R96.
The
voltage
divider
R94,
R95
produces
10.7
volts
at
the
base
of
Q9,
the
emitter
therefore
has
to
follow
0.7
volts
above
that
at
11.4
volts.
R96
therefore,
has
12
volts
on
one
side
and
11.4
volts
on
the
other
for
a
net
voltage
difference
of
0.6
volts.
This
0.6
volts
with
51
ohms
produces
approximately
12
ma
of
emitter
current
on
transistor
Q5.
The
output
of
transistor
Q5
is
lightly
coupled
into
a
MMIC,
a
buffer
/
amplifier
and
from
there
into
awide
band
amplifier
MAR-8,
which
produces
approximately
410
dBm
of.
power
output.
Also
coupled
to
the
VCO
at
the
output
of
MIC
amplifier
Q6
is
U12,
which
is
a
divide
‘py
4,
1
GHz
prescaler.
This
divides
the
output
of
the
VCO
by
4,
and
from
there
it
is
fed
into
U13
,
the
divide
by
10/11
dual-modulus
prescaler.
For
more
information
on
dual-modulus
prescaling
599
appendix
ል.
The
output
of
the
divide
by
10/11

Ramsey Electronics COM 3 Specifications

General

Brand	Ramsey Electronics
Model	COM 3
Category	Monitor
Language	English