Pioneer GEX-007(MB)EW Service Manual page 9

i-]—> eisley,
of QQ is lowered, attenuation is effected. These attenua-
tions due to the decrease in impedance enable AGC
operation. The input level to develop a voltage at pin 3 is
about 55 dBuV during reception of MW 999 kHz.
Thanks to the AGC operation mentioned above, the
output variation characteristics against input variation
are broader than the conventional AM characteristics.
7. AGC section (wide-band AGC) OUTPUT Characteristics of
(dB) conventional circuits
The wide-band AGC is to control the gain of the RF 0
amplifier section when the input RF level at pin 16 is
high. This is intended to prevent interference due to the -10
saturations of RF amp Q9, RF amp 1 in the IC, etc.
Caused by a large input other than the reception fre- -20 : —_ =
INPUT 10 20 30 40 50 60 (dBpVv)
quency.
Operation is as follows: A DC voltage corresponding Fig. 13
to the level of the input RF is developed at pin 2 by
amplifying and detecting the RF signal from pin 16 by
RF and 2 and detector 3 respectively. This is delayed by
the time constant of C75 and the gain of this portion is
determined by R58. By applying this DC voltage to AGC
amp 2, the AGC at RF amp 1 and AGC at Q7, D5 and
D6 are effected.
Characteristics of this
unit circuit
8. Stop signal
The stop signal for seek operation is produced by extract-
ing the IF signal from the secondary winding of T7 and
adjusting its level by VR5. This signal is connected via
450 kHz filter CF3 from pin 7 to IF amp 2 to detector 2.
This output appears at pin 6 and become OV during
reception.
9. Local station/distant station seek
During local station seek, Q8 turns on, whereby C43 is
grounded. The impedance of C43 allows attenuation in
the antenna system.
@® Frequency Synthesizer Section (FM)
During FM reception, a combination of synthesizer control
IC7 (the frequency dividing ratio is controlled to 1/64 or
1/66 by IC7) allow the slower counter method.
The FM VCO is frequency-divided to a ratio of 1/64 or
1/66 by prescaler IC7.
An output of 4.5 MHz (X2) which becomes a clock pulse
Antenna Synthesizer
Control IC
(| 0
Q22, 23
VCO FREQUENCY
for IC7 is divided into 1/360 by the reference frequency eM TUNING
1C7). Since the reception frequency is 87.5 ~ 108.0 MHz
and the intermediate frequency (IF) is 10.7 MHz, the oe aids
oscillator frequency
of VCO will be 98.2 ~
118.7 MHz.
Fig. 14
As the overall frequency division ratio is 7856 ~ 9496, the
output of the programmable counter inside IC7 will be
12.5 kHz. This output is compared in phase with a reference
frequency of 12.5 kHz by the phase detector in IC7, and
is output to pin 12 of IC7.
The loop filter consisting of Q22 and Q23 converts the
signal into a DC voltage signal which in turn controls the
tuning circuit in the front end section as a tuning voltage.
10