E F Johnson Company 2422001-1 Benutzerhandbuch
CIRCUIT DESCRIPTION
6-3
August 2000
Part No. 001-2001-200
Wideband Audio Amplifier
U204B amplifies the detected audio and data sig-
nal. R244/R245/R246 set the gain of the amplifier
and R247/R248/R249/R250/RT204 provide a DC ref-
erence level. C261 bypasses the 450 kHz IF signal
and C262 bypasses other frequencies. The output sig-
nal is adjusted by R253 and fed to J205, pin 3. Install
jumper plug P205 on J205, pins 2-3 to select the
12.5 kHz audio to be routed to J201, pin 9.
and R247/R248/R249/R250/RT204 provide a DC ref-
erence level. C261 bypasses the 450 kHz IF signal
and C262 bypasses other frequencies. The output sig-
nal is adjusted by R253 and fed to J205, pin 3. Install
jumper plug P205 on J205, pins 2-3 to select the
12.5 kHz audio to be routed to J201, pin 9.
RSSI Amplifier
U203, pin 13 is an output from an internal RSSI
(receive signal strength indicator) circuit which pro-
vides a current proportional to the strength of the
450 kHz IF signal. The RSSI output is buffered
through U204A and the level is adjusted by R221.
The DC output signal is then fed to J204, pin 3.
Install jumper plug P204 on J204, pins 2-3 to select
the 12.5 kHz RSSI to be routed to J201, pin 7.
vides a current proportional to the strength of the
450 kHz IF signal. The RSSI output is buffered
through U204A and the level is adjusted by R221.
The DC output signal is then fed to J204, pin 3.
Install jumper plug P204 on J204, pins 2-3 to select
the 12.5 kHz RSSI to be routed to J201, pin 7.
6.1.5 25 KHZ IF
First mixer U101 mixes the receive frequency
with the first injection frequency to produce the 52.95
MHz first IF. Since high-side injection is used, the
injection frequency is 52.95 MHz above the receive
frequency. Jumper J203 selects between a 12.5 kHz
MHz first IF. Since high-side injection is used, the
injection frequency is 52.95 MHz above the receive
frequency. Jumper J203 selects between a 12.5 kHz
IF and a 25 kHz IF. Install jumper plug P203 on J203,
pins 1-2 to select the 25 kHz IF. The output of U101
is matched to the crystal filter at 52.95 MHz by L201,
C201 and C202.
pins 1-2 to select the 25 kHz IF. The output of U101
is matched to the crystal filter at 52.95 MHz by L201,
C201 and C202.
Z201A/B form a two-section, four-pole filter
with a center frequency of 52.95 MHz and a -3 dB
bandwidth of 15 kHz. This filter attenuates adjacent
channels and other signals close to the receive fre-
quency. The filter is a matched pair and the dot on the
case indicates which leads connect together. Match-
ing with Q201 is provided by C205, L203 and C206.
bandwidth of 15 kHz. This filter attenuates adjacent
channels and other signals close to the receive fre-
quency. The filter is a matched pair and the dot on the
case indicates which leads connect together. Match-
ing with Q201 is provided by C205, L203 and C206.
IF Amplifier, Crystal Filter
Q201 amplifies the 52.95 MHz IF signal to
recover filter and mixer losses and improve receiver
sensitivity. Biasing for Q201 is provided by R204/
R201/R202/R203 and C207/C209/C211 provide RF
bypass. The output of Q201 is matched to crystal fil-
ter Z202A at 52.95 MHz by C210, C212 and L204.
sensitivity. Biasing for Q201 is provided by R204/
R201/R202/R203 and C207/C209/C211 provide RF
bypass. The output of Q201 is matched to crystal fil-
ter Z202A at 52.95 MHz by C210, C212 and L204.
Z202A/B form a two-section, four-pole filter
with a center frequency of 52.95 MHz and a -3 dB
bandwidth of 15 kHz. This filter establishes the selec-
tivity of the receiver by further filtering the
52.95 MHz IF. The filter sections are a matched pair
and the dot on the case indicates which leads connect
together. Matching with U201 is provided by C215,
C216, C217, L206 and R205.
bandwidth of 15 kHz. This filter establishes the selec-
tivity of the receiver by further filtering the
52.95 MHz IF. The filter sections are a matched pair
and the dot on the case indicates which leads connect
together. Matching with U201 is provided by C215,
C216, C217, L206 and R205.
Figure 6-3 25 kHz IF RECEIVER BLOCK DIAGRAM
BANDPASS FILTER
L102/L103/L104
A201
RF IN
U103A
BANDPASS FILTER
L108/L109/L110
U101
MIXER
Z201A/Z201B
CRYSTAL FILTER
52.95 MHz 4-POLE
RF AMP
IF AMP
Q201
CRYSTAL FILTER
52.95 MHz 4-POLE
Z202A/Z202B
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
Z203/Z204
U201
IF DETECTOR/AMP
AUDIO
U202B
U202A
RSSI
RX WBAND
VCO
Q131
Q132
Q132
BUFFER/AMP
VCO
FIRST
SECOND
INJ AMP
INJ AMP
Q133
Q134
L140/L141
INJECTION FILTER
BANDPASS
U102
AMP
INJECTION
TEST VOLTAGE
A006
Q204
MULTIPLIER
Q203
AMPLIFIER