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.t.NTENNA
01
PN2222A
990-2"
10~-iz
AM
RECIVER MODULE
UI
CET-
1003A
U4
MCl45170P
1MHz
U6
MICROPROCE:SSOR
PIC16C55HS
lOOkHz
lOkHz
J,
AUD
IO OUT
---------
10
SP(
AMP
80
----
9A1.ANCC0
OUTPIIT
TO
M
ODEL
911
TP1
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RSSI
V
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1
-5V
0
LOCA
L AUDIO
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Figure S-2.
AM
Receiver Module - Block Diagram
5.4
FM
Receiver Module Block Diagram Description
J2
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•LA~M
O~T
--'-
AUD
IO N
(~NIIALA~CCD
)
•
AUD
,O OUT
(UN8AL,lNC[O)
The
FM
Receiver
module
is tunable from
88
to
108 MHz in 100
kHz
steps. Audio output for external
use is balanced
600Q
at
up
to
+3
dBm.
Tuning
is
via three rotary switches which are accessible
by
removing the associated front panel cover plate.
An
LED
lights to
show
adequate
RF
signal level and
the presence
of
audio modulation.
Figure 5-3
is
a block diagram
of
the
FM
Receiver module. (See Figure A-5
in
Appendix A for the
sc
hematic diagram.)
The
following is a summary
of
the
operating principles
of
this module.
a. The
FM
Receiver module receives 88 to 108 MHz
FM
program signals at its rear panel RF
INPUT connector.
The
RF
signal is routed to front
end
block
Ul
consisting
of
a mixer, a
voltage-controlled oscillator (
VCO)
, a 10. 7
1v11-lz
IF
filter, and an
FM
Detector and other
components.
b.
The
detected audio signal is routed
to
relay K 1, along with the AUDIO
IN
from the backup
receiver module.
If
the
module
lo
ses
RF
or
modulation, and the
AlITO
SWITCH
strap (not
s
hown
)
is
in the
ON
position, the backup audio will
be
amplified
by
U3
for output.
If
the
AUTO
SWITCH
strap is in
the
OFF
position, the receiver audio will routed
to
U3 for output.
c.
The
se
lected audio signal from U 1 is amplified
by
U3
and sent
to
a BALANCED AUDIO
OUTPUT terminal block connector
on
the rear panel. The audio output level from the
Receiver board is adjustable via potentiometer
R4
which is accessible from the rear panel.
5-3
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General