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d.
Frequency selection is performed
by
a 3-digit rotary
DIP
switch along with microprocessor
U7
and
a
PLL
synthesizer consisting
of
US,
U6
,
Ql
, Q2, and
other
components.
e.
Th
e output
at
pin 10
of
U 1 is a
DC
voltage analog
of
the RSSI (
RF
level)
of
the input signal.
ANTENNA
This output can
be
measured
by
using a DC voltmeter at
TPl
which is accessible by
removing the associated front pane] cover plate.
FM RECIVER MODULE
J4 AUDIO
OU
T
~--
......,
.>-
,.._____
TO
~--
-
--<
Mo
J:t
111
RF IN
88•108
'-I
IU
u
>A
l
MJ2
ai;~~o
I V
LF3
4
7N
0 1
PN36&3
TP1
88
.7·118.7MHz
10MHz
U6
MICROPROCESSOR
PIC16CSSHS
1MH
z
100kHz
+6V
CR
1
RFI A\JOIO
0ET
Figure 5-3.
FM
Receiver Module - Block Diagram
5.5 NOAA Weather Receiver Module Block Diagram Description
The NOAA Weather Receiver module
is
tunable narrow-band
FM
Receiver that covers all seven
we
ather channels. Audio output for external use is balanced
600Q
at
up to +3
dBm
. Tuning is via
a?
-
position rotary
sw
itch wh
ich
is acce
ss
ible
by
removing the associated front panel
cove
r plate. An LED
lights
to
show adequate
RF
signal level
and
the presen
ce
of
audio modulation.
Figure 5-4 is a block diagram
of
the NOAA Weather Receiver
board
. (S
ee
Figure A-7 for
th
e
schematic.)
Th
e following is a s
ummary
of
the
operating principles
of
this module.
5-4
a. The NOAA Weather Receiver module receives 161
.4
to 16
2.55
MHz
narrow-band FM
signals
at
its rear panel RF INPUT connector.
Th
e
RF
signal
is
bandpass filte
red
, then
amplified by Q l .
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