Multitone RPR 561, Technical Manual

Page: 42 / 109

OSCILLATOR/
DOUBLER/
AMPLIFIER DRIVER
FL301
SAW
TR327
DRIVER
PA
TR15/16
CLAMP
Tx TONE
MIC
SUMMING
AMPLIFIER
IC5a
DTMF
RV301
MOD GAIN
TR301 TR302 TR303
TR307
LOW-PASS
FILTER
AE301
TR18
TR22
LOW-PASS FILTERS
TR21, TR17,
TAG10661-1
TRIPLER
XL301
AMP
IC5b
IPA
TR306
BUFFER/
T303
T302
RPR 561
TM1200 Issue 1 Page 3 - 7
Figure 3: Radio Board - Transmitter Block Diagram
Transmitter
24. A block diagram of the transmitter is shown in Figure 3.
25. Amplified microphone speech from PL301 pin 8 is clamped by TR15/TR16 before
application to the two low-pass filters formed by TR17/TR18 and TR21/TR22. The
filters limit the audio bandwidth to 3kHz. After filtering the signal is applied via R52 to
IC5a.
26. The sub-audio tone derived from IC2 (see paragraph 24) is applied to IC306 via
potential divider R65/R64. When DTMF tones are generated by the Decoder Board,
they are applied to IC5a via R37, R38 and R60. The tones are also applied to IC5b for
amplification, rectified by D1 and C42, and applied to TR14, which mutes the speech
circuits from the microphone. This allows DTMF tones to be transmitted without speech
superimposed.