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WJ-8711A
SELECTABLE
REMOTE CONTROL
A N T E N N A
I N P U T
E XTERNAL
REFER ENC E
1, 2, 5, 10 MHz
D C P O W E R
P O W E R
A C P O W E R
S U P P L Y
WJ-8711A Functional Block Diagram
Functional Description
Figure 2 illustrates how the WJ-8711A is divided into
four functional subsystems: RF, DSP, IF/Audio
Output and Control. Figure 3 provides a functional
block diagram of the RF Subsystem. The 5 kHz to
30 MHz RF signal is applied to the receiver's antenna
input, lowpass filtered, and then amplified, attenuated
or routed to the normal through-path based on user
selection. The signal is then mixed with the first local
oscillator (LO), which tunes from 40.455 MHz to
70.455 MHz in 1-kHz steps, to produce a first IF of
40.455 MHz. The first IF filter limits the bandwidths
of the signal to approximately 30 kHz before mixing
it with the 40-MHz second LO to produce a second IF
at 455 kHz. A sample of this second IF is provided on
a rear panel for connection to a signal display unit.
RS-232
CSMA
PRESELECTOR
(OPTIONAL)
R F G A I N
C O N T R O L
RF
3 RD IF
SUBSYSTEM
FRONT
PAN EL
CONTROL
CONTROL
SUBSYSTEM
T I M I N G
& CO N TR OL
DSP
SUBSYSTEM
D A T A
INTERNAL
SPEAKER
(O PTI ONAL)
RSSI
SQUELCH OUT
MU TE
After passing through the second IF filter, the signal
is mixed with the 430-kHz third LO to produce the
third IF centered at 25 kHz.
All LOs are derived from an internal 10-MHz
oscillator that can be locked to an external reference
input of 1, 2, 5 or 10 MHz. The WJ-8711A auto-
matically senses and switches to the external refer-
ence upon application of signal. All critical timing
signals used in the DSP and IF/Audio Output
Subsystems are also derived from this reference.
The DSP Subsystem performs the majority of the
receiver's signal processing functions. The third IF
signal from the RF Subsystem is digitized to 16 bits
of resolution at a sampling rate of 100 kHz. This
digitized IF signal is applied to a programmable
DSP chip that performs the following functions
4
FRONT
HEADPHONE
PANEL
OUTPUT
ASSEMBLY
AUDIO
VO LUME
HEADPHONE
CONTRO L
AUDIO
IF/AUDIO
OUTPUT
SUBSYSTEM
SPEA KER OU TPUT
LINE AUDIO A
LINE AUDIO B
DC-A UDIO
IF OUTPUT
SIGNAL MONITOR
OUTP UT
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