DRAKE SPR-4 Specifikace Strana 17

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to one gate of the premixer, Q5 through C26 and
R15.
The P.T.O. drives
the other gate of Q5 through R25 and C76. The P.T .O. is tuneable from
4955 kHz to 5455 kHz.
The output of Q5 is tuned by the components associated with
S4F,
S4R,
S8F,
S8R
and drives the 1st mixer through T6,
S6R,
C99
and C96.
4.5
SECOND MIXER
The 2nd mixer,
Q10,
is driven by the 1st mixer and
the crystal
oscillator
buffer Q17.
Q10 is coupled to the 1st IF amplifier through the T notch
filter
and the 50 kHz four pole Hi-Q ferrite LC
filter.
Heterodyning of
the 1st mixer and
crystal
oscillator results in a
difference
frequency
out-
put from Q10 of
50
kHz.
4.6
1. F. SYSTEM
The I .F . system is composed of the 1st I .F . amplifier, 423, which drives
through T 15, the 2nd
I.
F. amplifier, Q24.
C169 and C187
tune
T15
and
T16 respectively to 50 kHz and T16 drives the
detection
systems .
4.7
DETECTION SYSTEMS
4.7.1 AM DETECTION
The AM signal from
T16
is detected by CR2 1 and amplified by Q28 to a
level matching
the output level of the product detector and is applied to
the audio gain control through C 167 and S 14F.
4.7.2 CW AND SSB DETECTION
CW and SSB signals from T16 are detected by the product detector made
up of CR19, CR20, R122, R123, and Q27, the beat frequency oscillator.
The output of the product detector is applied to the audio gain control
through S 14F.
4.8
AUDIO AM
PLIFIER
A portion of the audio signal, determined by the setting of
Rl0l
, is
ap-
plied to Q22 through a low-pass
filter
consisting of L10,
L11,
C164,
R97,
R95,
C 163, and C159 which eliminates
any
residual 50 kHz signal
from driving the audio amplifier.
Q22 amplifies this audio signal and
drives
Q20
through C 148 where further amplification occurs and Q2 0
drives
Ql6
directly and
Q15
via Q19 which is
unity
gain
common
base
amplifier. Q12, Q 15 and
Q13,
Q16 are darlington connected amplifiers
and the configuration of Q16 establishes a phase inversion permitting
Q12 and Q13
to
operate in push-pull, Q12 and Q13 operate the speaker
or a headphone through coupling capacitor C
127.
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15 -
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