Kenwood TS-440S Serivce Manual page 15

TS-440S
CIRCUIT DESCRIPTIO N
4) Speech processo r
IC4 in the IF unit functions as the first stage microphone am -
plifier or audio speech processor . When the processor switc h
is off, IC4 functions as a 20 dB microphone amplifier . Whe n
the processor switch is on, IC4 functions as an up to 40 d B
PROCESSOR OF F
ON
Fig . 1 1
MIC
gain amplifier with ALC . When the processor switch is on ,
8 VDC is supplied to the base of the gain adjustment switch -
ing transistor, Q41, driving the feedback amplifier .
GAIN 2Od B
MAX GAIN 4Od 8
4 . PLL Circuit s
Theory
of
PLL
circuit
operation s
The TS-440 PLL circuit uses a reference frequency of 36 MH z
and consists of five PLL loops covering the range of frequen -
cies from 30 kHz to 30 MHz in 10 Hz steps . The PLL circui t
has an IF shift function which is implemented by insertin g
carrier frequencies between PLL loops . The PLL loops includ e
a carrier circuit PLL loop and an HET circuit PLL loop whic h
generates a constant frequency of 36 .22 MHz . Frequenc y
division for these PLL loops is controlled by the microproces -
sor . In all PLL loops phase comparison is made using the refer -
ence frequency fSTO (frequency control using a single crysta l
oscillator) .
Figure 12 is the PLL circuit block diagram .
The reference frequency (fsro) is generated by a 36 MH z
crystal oscillator and Q21 (2SC2787) . Reference frequenc y
signals are fed into the main loop's IC1 1 (SN16913P) via a
buffer consisting Q22 and Q23 (2SC2668) . The signal is als o
fed into IC13 (SN74S112) via a buffer consisting of Q2 4
(2SC2668) . In IC13, the signals are frequency divided t o
generate a 9 MHz signal . The 9 MHz signal is used as th e
reference frequency signals for the PLL loops .
• PLL 5
PLL5 consists of IC 18 (MN6147) and its associated loo p
components . VCO5,Q36 (2SK192A), is locked at a fre-
quency of 36 .22 MHz . The 9 MHz reference frequenc y
signal is supplied to pin 3 of IC 18, where the signal is divid -
ed by 1800 (450 in FM mode) to generate
a
5 kHz (2 0
kHz in FM mode) signal used for comparison . VCO5's out -
put signal is supplied to IC 18 pin 16 via Q37 (2SC2668) ,
where the signals are frequency divided by 7244 (181 1
in FM mode) . The phase of the signal is then compare d
with that of the 5 kHz (20 kHz in FM mode) signal by th e
phase comparator and the VCO5 oscillation frequency i s
locked . Frequency division data is supplied by digital uni t
(DAO to DA3 and CK4) .
As described above, the dividing ratio used varies depend -
ing on which mode the TS-440 is in, FM mode or SSB .
This is because the apparent time constant is increase d
without changing the active LPF constant so that the PL L
signals can be modulated easily and reducing distortio n
during FM transmission . In modes other than FM, th e
amount of frequency shift due to mechanical vibration s
is reduced because the apparent time constant is reduced .
The output from PLL5 goes through buffer Q38 (2SC2668 )
and LPFs, and is used as the HET signal in the RF unit .
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