Table of Contents
Advertisement
9Sr
(d)
Reception filter
and
comparator circuitry
As shown
in Fig.
52,
the
reception circuit input signal passes
through
the coupling capacitor
(C40)
,is
then amplified, passes
through
the 3-stage band-pass filter (composed of an
active
filter)
,
is
then amplified once again
,
passes through the
comparator
,
and, then
after being changed
to
a
square wave,
is
input at the RX CAR terminal of MC14412.
The intermediate frequencies
of the
3-stage active filter
are shown
in
the chart below.
The switching of the intermediate frequency for the .originate
mode and
the answer
mode
is
accomplished
by
switching T2,T3
and T5 ONor OFF according to the ORIG- ANS
switch setting,
thus
changing the value
of R16,R28 and R25.
The transmit carrier signal output from the TX
CAR terminal
is
DC by
C61,and the signal level
is
adjusted
to -26.5 dB by
the control
(VR2)
.
The signal then passes
through
the
transmission
filter (band-pass filter) and
is
sent
to the
telephone line
or the
acoustic coupler.
The transmission filter
is
composed of
an
active filter
consisting
of an
operation amplifier
,and the
intermediate
frequency must
be
switched according to the mode (originate
or answer)
Depending
on the
ORIG-ANS switch setting
,the
transistor
T4
'
is
ON or OFF,
so
that R42
is
2.3K
for the
answer mode, and the
synthesis resistance
of
the R42 and
R4
5
value determines the
originate mode
.
The intermediate frequency of the active filter
is 117 0Hz
for the
originate mode
,and
2125Hz for the answer mode.
- Quick Links:
- Table of Contents
Hide quick links:
Advertisement
Table of Contents
