JRC NDR-91 User Manual

5.
CIRCUIT
DESCRIPTION
Refer to
the
annexed
blockdiagram
for
the
circuit
composition
of the receiver.
This
receiver
is
composed
of
receiving,
local signal
generator,
panel
and
power
supply
sections.
5.1 RECEIVING
SECTION
The
receiving
system is
an
up-conversion
type double-superheterodyne
with
a first
intermediate
frequency
of 70.455
MHz
and
a
second
intermediate
frequency
of
455 kHz.
A
signal
frequency
of 90 kHz
to 29.9999
MHz
is supplied
to
the RF
input filter
after
passing
through
the BK relay
and
the input
protection
circuit.
The
signal
thus
supplied
passes
through
the 35 MHz
LPF
and is
supplied
to one
of the seven filter
circuits,
depending
on
the operating frequency.The
signal
is
then fed
into
the lst
Mix. in
whichthereceiving
signal
is
mixed
with
the first
local signal
of 70.545
to
100.4549
MHz
and is thereby
converted into
the first
IF
of
70.455 MHz.
The
converted output
passes
through
the
crystal
filter with
a
center
frequency
of
70.455
MHz
and a bandwidth
of l2kHz,
and
then is
amplified
by
the
lst
IF
AMP.
Then the
siganl is supplied
to
the
2nd
IF
in which
the
amplified
signal
is mixed with
the 2nd
local
frequency
signal of
70 MHz
and is thereby
converted into
a
2nd
IF of 455 kHz.
The
converted
output
passes
through
one selected
out
of three filters with
bandwidth
of 6 kHz,
3
kHz
and 0.5
kHz
and
the filtered
signal
is
amplified
by the 455
kHz
IF AMP.
2
r'J
The amplifed receiving
signal is
supplied
to
the
AGC circuit
and demodulator
circuit
respectively.
The AGC voltage for
automatic
gain
control is
applied
to the lst
IF
AMP
(70.455
kHz)
and 2nd
IF AMP
(455
kHz.).
In case of
DSB detection,
the demodulator
circuit takes out the
carrier component
from
the receiving frequency
signal
and operates
as
a synchronous detector.
In
case
of
other than
DSB detection,
the BFO
signal supplied
from
the
BFO circuit and the demodulator
circuit operates
as
a
product
detector.
The demodulated output
is supplied
to
AF
AMP and LINE
AMP respectively.
AF AMP
is
a AF
power
amplifier for
speaker
and headphones.
The
gain
is
adjusted
by
IC
for
electronic volume
placed
on the fbrmer
stage
of
AF
AMP according
to the DC
voltage
supplied fiom
AF GAIN
controller
on the front
panel.
The
LINE AMP output
is supplied
to
[BRE-
LINEI
connector
on the rear
panel
and
used for
connecting to the tape recorder,
FAX,
FSK
demodulator,
etc.
The LINE
AMP
output is approx. 0
dBm which
is not
affected by
the AF
GAIN
controller
on
the
front
panel.
The BK circuit is
provitled
for
protecting
from
burning due
to the inducation
of
own
station's transmitting
radio
wave.
This BK
circuit
is controlled
by the
external
+BK
and
-BK
(keying
signal). When
-BK
line becomes 0V
(keyed),
the BK circuit
operates for
grounding
the
antenna terminal.
At
the same time,
since
the AGC circuit is
controlled,
the
gain
of the
receiver
is reduced
and
the speaker
output does not
appear
(muting
condition).
5.2 LOCAL SIGANL GENERATOR
SECTION
The
local signal
generator
section
is composed
of the lst local
oscillator,2nd
local
oscillator
and BFO circuit.
-16-

JRC NDR-91 Specifications

General

Brand	JRC
Model	NDR-91
Category	Receiver
Language	English