Table of Contents
Advertisement
CIRCUIT DESCRIPTION
BANDPASS
FILTER
A201
L201/L202/L203
RECEIVE
RF IN
OCXO IN
HIGH STABILITY
SYNTHESIZER
REF
IN
HS CS RX
EN
HS LK RX
LD
U205
F IN
CLK
DATA
PD
OUT
MAIN
SYNTHESIZER
REF
IN
RF DATA
DATA
RF CLK
CLK
U209
F IN
SYN CS RX
EN
SYN LK RX
LD
PD
OUT
6.1.6 SECOND MIXER/DETECTOR (U202)
As shown in Figure 6-2, U202 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 Y201 and tripler
Q205. The 17.5 MHz (±0.1 PPM) output of Y201 is
fed through C231 to tripler Q205. The tripler passes
the third harmonic at 52.5 MHz to the OSC B input of
U202.
Biasing of Q205 is provided by R228, R227 and
R229. RF choke L214 blocks the flow of RF through
R229. An AC voltage divider formed by C236/C235
matches Q205 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. L215, C237 and L216
form a high pass filter to attenuate frequencies below
52.95 MHz. C222 and C238 match the output of the
filter to U202.
October 1999
Part No. 001-2009-201
BANDPASS
RF AMP
FILTER
Q201
L204/L205/L206
Q203
Q204
BUFFER
Q210
Q211
17.5 MHz TCXO
Y201
BUFFER
Q210
Q211
BUFFER
Q208
Q209
BUFFER
VCO
A006
Q214/Q215
Figure 6-1 RECEIVER BLOCK DIAGRAM
52.95 MHz 4-POLE 52.95 MHz
MIXER
CRYSTAL FILTER
U201
Z201/Z202
843-848 MHz
TX OCXO
52.95 MHz
QUADRATURE DETECTOR/2ND MIXER
U202
MULTIPLIER
BPF
L215
Q205
L216
Z205
450 kHz
52.5 MHz
L223
BANDPASS
FILTER
L224
AMP
AMP
Q216
U204A
Q217
OSC B 1
OSC E
2
MIXER OUT
3
Vcc
4
IF IN
5
DECOUPLING 1
6
7
DECOUPLING 2
QUAD COIL
8
Figure 6-2 U202 BLOCK DIAGRAM
6-2
52.95 MHz 4-POLE
IF AMP
CRYSTAL FILTER
Q202
Z203/Z204
RSSI
U203A
AUDIO AMP
U203B
TP
RX INJ
MIXER
LIMITER
AMP
AMP
FILTER
AF
AMP
RSSI
RX WB AUD
16 MIXER IN
15
GROUND
14
MUTE
13
RSSI
12
SQUELCH IN
11
FILTER OUT
10
FILTER IN
9
AUDIO
Advertisement
Table of Contents
