Revox B261

sTrtJDtrR
nd/ox
8261
SA
sEcTroN 3/2
3.2
RF
INPUT SECTION
BANDPASS
ANTENNA
1ü RF-At\rPLl
CIRCUIT
FIER STAGE
llh
DOUBLE TUNED
2'd RF
AMPLI-
CIRCUIT FIER STAGE
BAUNCED
MIXER
PHASE LINEAR
,FILTER
TO IF.AMPLI'
FIER 1.726.740
87...108.0MH2
INP
NNA
.8
FROM IF-AMPLIFIER 1.726.1
40
+
AGC
FROM SYNTHESIZER
PCB 1.1 26.1
7
o
+
3.2.1
RF amplifier
1.726.730
From the
75 ohm
IEC socket
or
the optional
antenna
selector
switch,
the
antenna
signal
is
conducted
through
the
FM band-
pass
to
the
RF i,nput.
Through
the antenna
circuit,
the
si-gnal
is taken to
the
first
RF amplifier
stage
Q1
(dual
gate
MOSFET).
The
gain
of
this stage
is
decreased
for
large
input
signals.
The
control
voltage
(AGC)
is
generated on
the
rF
ampl-ifier
),.726.1
40.
The amplifi-er
stage
is
followed by a
double-tuned
circuit
band-pass
fiLter.
After the second
RF amplifier
stage
Q2
and
the second tuned
band-pass
fj-1ter, the signal
is coupled
to
the
balanced mixing
stage
(Q4
and
Q5).
The tuning
voltage
for
the series-paralle1-connected
varactors of
the
bapd-pass
filter is
generated in the synthesizer
module.
3.2.2
Antenna
switch
An electronic
antenna
selector
switch
for changing over
between
two 75 ohm
fEC antenna sockets
A/B is
avail-able as a
retrof
itt
able
opt
j.on
.
3.2.3
Synthesizer
and
local- oscill-ator
1.726.770
The
local osciflator
with a buffer
stage
connected
to the
output supplies
its
signal
to the m.ixing
stage
on the RF
section as
well as to the synthesj-zer
module
(IC1
)
.
This
semiconductor
devj,ce
contains the complete
PLL
circuit
for
generating
the tuning
voltage for the varactors
of
the
1oca1
oscillators
and the
band-pass
filters
on
the
RF section.
The
quartz-accurate
local- oscillator
frequency
is
higher by
the IF
frequency of 10.7
MHz
than the
input
frequency.
The
frequency steps are
r-2.5
klH,z. A1l
operating
data and controf
information are transferred
by the microprocessor
to the
snythesizer
module through
the serial CBUS
interface.
ANTENNA SWITCH
Uro
(98.2...118.7
MHz)
4.5...24v