E F Johnson Company 2422001-1 Benutzerhandbuch
CIRCUIT DESCRIPTION
6-2
August 2000
Part No. 001-2001-200
Part No. 001-2001-200
Figure 6-1 12.5 kHz IF RECEIVER BLOCK DIAGRAM
BANDPASS FILTER
L102/L103/L104
A201
RF IN
U103A
BANDPASS FILTER
L108/L109/L110
U101
MIXER
Z211A/B
CRYSTAL FILTER
52.95 MHz 4-POLE
RF AMP
IF AMP
Q202
CRYSTAL FILTER
52.95 MHz 4-POLE
Z212A/B
U401
SYNTHESIZER
RF DATA
RF CLOCK
SYN CS RX
SYN LK RX
BUFFER
Q401
Q402
Q402
BUFFER
Q410
Q411
Q411
REF IN
V
R
F IN
Q406, Q407
Q408, Q409
Q408, Q409
CHARGE PUMP
VOLTAGE MULTIPLIER
Q403, Q404
Q405, CR402
Y401
17.5 MHz TCXO
Q204
MULTIPLIER
Z213/Z214
U203
IF DETECTOR/AMP
AUDIO
U204B
U204A
RSSI
RX WBAND
VCO
Q131
Q132
BUFFER/AMP
VCO
FIRST
SECOND
INJ AMP
INJ AMP
Q133
Q134
L140/L141
INJECTION FILTER
BANDPASS
U102
AMP
INJECTION
TEST VOLTAGE
A006
Biasing of Q204 is provided by R258, R259 and
R260. RF choke L222 blocks the flow of RF through
R261. An AC voltage divider formed by C280/C281
matches Q204 to the highpass filter. The third har-
monic of the TCXO frequency is then used to drive
the OSC B input at 52.5 MHz. L223, C282 and L224
form a high pass filter to attenuate frequencies below
52.95 MHz. C283 and C284 match the output of the
filter to U203.
R261. An AC voltage divider formed by C280/C281
matches Q204 to the highpass filter. The third har-
monic of the TCXO frequency is then used to drive
the OSC B input at 52.5 MHz. L223, C282 and L224
form a high pass filter to attenuate frequencies below
52.95 MHz. C283 and C284 match the output of the
filter to U203.
The 450 kHz second IF is then fed to ceramic fil-
ter Z213/Z214, then into the IF amplifier. The center
frequency of Z213/Z214 is 450 kHz with a bandwidth
of 9 kHz used to attenuate wideband noise. The lim-
iter amplifies the 450 kHz signal 92 dB which
removes any amplitude fluctuations.
frequency of Z213/Z214 is 450 kHz with a bandwidth
of 9 kHz used to attenuate wideband noise. The lim-
iter amplifies the 450 kHz signal 92 dB which
removes any amplitude fluctuations.
From the limiter the signal is fed to the quadra-
ture detector. An external phase-shift network con-
nected to U203, pin 8, shifts the phase of one of the
detector inputs 90
nected to U203, pin 8, shifts the phase of one of the
detector inputs 90
°
at 450 kHz (the other inputs are
unshifted in phase). When modulation occurs, the fre-
quency of the IF signal changes at an audio rate as
does the phase of the shifted signal. The detector,
which has no output with a 90
quency of the IF signal changes at an audio rate as
does the phase of the shifted signal. The detector,
which has no output with a 90
°
phase shift, converts
the phase shift into an audio signal. Z215 is adjusted
to provide maximum undistorted output from the
detector. The audio signal is then fed out on U203,
pin 9.
to provide maximum undistorted output from the
detector. The audio signal is then fed out on U203,
pin 9.
Second Mixer/Detector
As shown in Figure 6-2, U203 contains second
oscillator, second mixer, limiter, detector and RSSI
circuitry. The 52.95 MHz IF signal is mixed with a
52.5 MHz signal produced by TCXO Y401 and tripler
Q204. The 17.5 MHz (
circuitry. The 52.95 MHz IF signal is mixed with a
52.5 MHz signal produced by TCXO Y401 and tripler
Q204. The 17.5 MHz (
±
2.5 PPM) output of Y401 is
fed through C275 to tripler Q204. The tripler passes
the third harmonic at 52.5 MHz to the oscillator input
of U203.
the third harmonic at 52.5 MHz to the oscillator input
of U203.
Figure 6-2 U201/U203 BLOCK DIAGRAM
MIXER
LIMITER
OS
AMP
DEM
ODU
LA
T
O
R
AMP
AMP
FILTER
S
QUE
LC
H T
R
IGGE
R
W
IT
H
H
S
T
ER
ES
IS
AF
QUAD COIL
DECOUPLING 1
DECOUPLING 2
GROUND
SQUELCH IN
FILTER OUT
FILTER IN
RSSI
AUDIO
9
10
11
12
13
MUTE
14
15
16 MIXER IN
IF IN
Vcc
MIXER OUT
OSC E
7
6
5
4
3
2
OSC B 1
8