433MHz Narrow Band Radio Transmitter & Receivers
Functional Description
The QBT37-XXX FM narrow band transmitter
module consists of a low frequency directly
modulated crystal oscillator and multiplier and
filter circuits. Baseband data directly modulates
the low frequency crystal oscillator, the output of
which is applied to the first of three frequency
multipliers to achieve the final output frequency
after being processed by interstage band pass
filter circuits.
The QBR37-XXX FM narrow band receiver
module uses the single conversion super-het
principle. The applied RF signal is amplified and
applied to the RF mixer. Using a 10.7 MHz IF
frequency at 50KHz channel spacing enables use
of ceramic filters to provide good adjacent channel
rejection. Baseband demodulation is recovered
from this IF and applied to a squelch circuit.
Therefore, data is only available when a RF signal
is present.
Frequency Channels
The QBT37-XXX and QBR37-XXX are available
in 34 discrete frequency channels from 433.075 to
434.725 MHz in 50KHz steps. The table below
shows the list of possible frequency channels.
+5V
100k
Ω
10k
Ω
Ω
X1
Q1
CV1.
FREQ.
ADJ.
Q2
Q3
Q4
CH.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
FREQ/MHz
433.075
433.125
433.175
433.225
433.275
433.325
433.375
433.425
433.475
433.525
433.575
433.625
433.675
433.725
433.775
433.825
433.875
CH.
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
FREQ/MHz
433.925
433.975
434.025
434.075 (1)
434.125
434.175
434.225
434.275
434.325 (1)
434.375
434.425
434.475
434.525 (1)
434.575
434.625
434.675
434.725
100k
Ω
470pF
D1
15k
Ω
(1) Stock Item
AUX
2
3
4
5
6
7
1
2.5VDC
+5V
0.1
µ
F
3V
ANALOGUE MODULATION
RF OUTPUT
Z = 50Ω
Ω
5V
DIGITAL MODULATION
0V
+5V
IC1
+5V
Q1
X1
Q2
CV2
FREQ.
Q3
XF1
XF2
22KΩ
Ω
1
2
3
4
5
6
7
8
9
+5V RF
ANT 50Ω
Ω
100mV
RSSI
+5V IF
0.1
µ
F
ANALOGUE OUTPUT
5V
DIGITAL OUTPUT
20Hz - 10KHz
0V
Figure 3: Narrow Band Transmitter and
Receiver Block Diagrams
DS337_2
June 01
©
2001 REG No 277 4001, England.
Page 5
RFSOLUTIONS [ RFSOLUTIONS.LTD ]
