Sony HP-210 - Page 6

Stage/Control
Mixer Q102
Fm I-f Amplifier
I-f amplifiers
Q201 to Q204
I-f output
Q205
Function
lator frequency changes by taf.
This means that the new inter-
mediate frequency is 10.7 MHz
+af. See Fig. 1-1.
As the result a positive dc com-
ponent is fed back to the anode
of D101, decreasing the reverse
voltage to it, and making D101’s
barrier capacitance increase. This
decreases the local oscillator’s
frequency since the series circuit
composed of C119 and D101 is
connected in parallel with the
tank circuit of the local oscil-
lator. Conversely, if the local
oscillator frequency decreases, a
negative dc voltage is fed back to
D101, increasing the local oscil-
lator frequency.
Rf signals and local-oscillator
voltage are heterodyned in the
base-emitter junction of mixer
Q102 to produce 10.7-MHz i-f
output signal. Transformer IFT-
._ 101 and capacitors C105 and
C106 form a high “C’’, pi-net-
work bandpass
passes the i-f output and pro-
vides a path to ground through
~ C105 and C106 for the other
heterodyne products and oscil-
lator harmonics.
The i-f amplifier stages consist
of two pairs of direct-coupled
amplifiers that provide essen-
tially flat response. The
selectivity of this section is
determined by two-pairs of
filters (CF201, CF202, CF203,
and CF204) in the inter-stage-
coupling path. Each of these
filters is a two-section ceramic
filter that operates in the
“trapped-energy” mode. The
filters provide extremely sharp
skirt selectivity and flat response
inside the pass band. These
filters determine overall selec-
tivity in the fm tuner.
Q205 provides power to drive
the ratio detector.
filter, which ©
Stage/Control
~ Ratio detector
IFT201, D201,
D202
MPX Decoder
SCA trap coil
L301, C306
19-kKHz
amplifier Q303
Fig. 1-1
Function
IFT201: and diodes D201 and
D202 form a balanced ratio de-
tector that transformes the fre-
quency-modulated signal into an
audio signal. Output appears
across C207.
The composite signal containing
monaural information from 0 to
15 kHz, the 19 kHz pilot carrier
and the stereo signal at 38 kHz
+15 kHz is fed to the MPX de-
coder through a trap consisting
of L301 and C306. This trap
removes the -unwanted SCA
signals (67 kHz) to feed a clean
composite signal to the base of
Q303.
This stage serves two functions.
It extracts the 19-kHz pilot
signal by means of a tuned
circuit at its collector, and pro-
vides a low-impedance source of
composite stereo signal (without
_the pilot carrier) at its emitter.
Series-resonant circuit in the
emitter circuit eliminates the
19-kHz pilot signal from the
composite stereo signal.
local oscillator freq.
10.7 MHz
RF signal
“S” curve
response
% Af: frequency drift
Lacal oscillator frequency drift and
- afc voltage relation