Circuit Description - Kenwood R-2000 Service Manual

R-2000
CIRCUIT DESCRIPTION
Item
Rating
Center frequency 455 kHz ± 0.6 kHz
6 dB band width
2.s
±0.3 kHz
40 dB band width 5.5 kHz or less
Insertion loss (at maximum output)
6.0 dB or less
Guaranteed attenuation 55 dB or more
(within 455 ± 100 kHz) ,
Spurious attenuation
(within 0.1 to 1.0 MHz)
45 dB or more
for 600 to 700 kHz. 40 dB or more
1/0 matching impedance
2.0 k.Q
Table 2. Ceramic filter {L72-0332-05, RX unit F3)
SSS, AM-N, CW-W
Item
Rating
Nominal center frequency 455 kHz
6 dB band width
± 3 kHz or more
(from 455 kHz)
50 dB band width
± 9 kHz or less (from 455 kHz)
Ripple (within 455 ± 2 kHz) 2 dB or less
Insertion loss 6 dB or less
Guaranteed attenuation 60 dB or more
(within 455 ± 100 kHz)
1/0 matching impedance 2.0 k.Q
Table 3. Ceramic filter (L72-0319-05, RX unit F4)
AM-W
Item Rating
Nominal center frequency 455 kHz
6 dB bandwidth ± 7 .5 kHz or more
50 dB bandwidth ± 15 kHz or less
Ripple (within 455
±
5 kHz) 3 dB or less
Loss 6 dB or less
Guaranteed attenuation
35 dB or more
(within 455 ± 100 kHz)
Input and output impedance 1.5 k.Q
Table 4. Ceramic filter (L72-0316-05, RX unit F5)
FM
Item
Rating
Center frequency
fo
455.7 kHz
Center frequency deviation
fo
±50 Hz at 6 dB
6 dB bandwidth ±250 Hz or more
60 dB bandwidth
±425 Hz or less
Ripple 2 dB or less
Loss
6 dB or less
80dB or more
Guaranteed attenuation
at 100 Hz to 455. 1 kHz and
456.3 kHz to 2 MHz
lmput and output impedance
2kQ#'15 pF
Table 5. CW Crystal filter (L71-0206-05)
YG-455C (Option)
4
Item Rating
Center frequency quency
f
o 455.7 kHz
Center frequency deviation
Jo
±50Hzat6dB
6 dB bandwidth ± 1 25 Hz or more
60 dB bandwidth
± 250 Hz or less
Ripple 2 dB or less
Loss 6 dB or less
80 dB or more at
Guaranteed attenuation
100 Hz to 455.3 kHz and
456.1 kHz to 2 MHz
Input and output impedance
2 k.Q // 15 pF
Table 6. CW Crystal filter (l71-0207-05)
YG-455CN (Option)
PLL (Phase locked loop) unit XS0-1920-00
The PLL unit houses the PU. oscillator circuit, microproces-
sor control circuit and the NB amplifier circuits. In the PLL
circuit, there is a 9 MHz reference frequency crystal oscilla-
tor, the first local oscillator (45.90 ,..., 75.85 MHz), second
local oscillator (36 MHz) and third local oscillator (9.395 ,...,
9.445 MHz), which are output to the Receiver unit.
The digital circuit peripheral to the microprocessor controls
the PLL circuit frequency, display, clock/timer, input inter-
face, rotary encoder mode (speed) and memory.
1 . PLL circuit
1 ) Reference frequency oscillator
01 operates at a reference frequency of 9 MHz, which
is supplied to the second and third local oscillator cir-
cuits through buffer 02.
Via buffer 03, a 4.5 MHz signal divided 1 /2 by IC 1 is
supplied through buffer 04 to the first local oscillator
PLL circuit. The reference frequency is also buffered
(06) and divided down to 1 kHz by IC2 for use as a
clock reference signal.
2) First local oscillator circuit (LO 1)
The first local oscillator is obtained from the PLL
(Phase Locked Loop) circuit. Three VCOs (Voltage
Controlled Oscillator) controlled by the microproces-
sor through 020 ,.., 22 cover the 45.90 ,..., 75.85
MHz frequency range. The VCO output is amplified by
026. 027 and 028. Part of the signal is applied to
buffer 016:. 2SC1907 and PLL IC5: MN614 7C. The
spurious component is eliminated from the remaining
signal by a BPF and is output via. buffer 029 and
030: 2SC 1 707 as the LO 1 signal.
IC5: MN6147C consists of a programmable fre-
quency divider. reference frequency divider and phase
comparator which compares the reference and VCO
frequencies (comparision frequency; 25 kHz). The
programmable divider's ratio ( 1836 ,.., 3034; only
even number) is controlled by the microprocessor.
The phase error signal from the comparator is applied
to the VCO by active filter 017, 018 and 019:
2SC1775.
3) Second local oscillator (L02)
The reference frequency is quadrupled by 05:
2SC 1815 to obtain the 36 MHz second local oscilla-
tion frequency.