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5 . C I R C U I T D E S C R I P T I O N S
5 . 1 A M T U N E R
Composed of single IC (HA1138) combining a 1
stage RF amplifier and a 2 stage IF amplifier (Fig.
1 ) .
5 . 2 F M T U N E R
Front End
The outstanding performance, exemplified by the
remarkable 80dB imaging and
90dB
spurious
rejection, originates in the dual-gate MOS FET
RF amplifier and 4-gurg variable capacitor tuning
circuit. A modified Clapp circuit is employed in
the local oscillator, leading to high frequency
stability.
Since the output
is taken from the
oscillator tuning circuit, higher harmonics in the
oscillator signal and spurious response become
reduced.
sx-750
lF Amplifier and Detector
Comprise 2 dual element ceramic filters,
sistor, and 1 IC (integrated circuit).
(HA1137) circuit is illustrated in Fig. 2.
FM lF Amplifier and Detector Circuit
Three dual element ceramic filters, an IC (HA1201)
containing
a differential
amplifier,
and an IC
(HA1137) containing a 3-stage limiter amplifier
compose the FM IF amplifier. Fig. 2 shows the
HA1137 block diagram (see circuit diagram on
page 65).
In addition to limiter amplifier. the HA1137 IC
includes detector, meter drive circuits. The detec-
tor circuit in the HA1137 is not employed in this
set however a separate ratio detector circuit is
employed instead, resulting in improved S.N ratio.
1 tran-
The IC
F i g . 1 B l o c k D i a g r a m o f H A 1 1 3 8
F i g . 2 B l o c k D i a g r a m o f H A 1 1 3 7
1 3
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