Kenwood KT-7020 Service Manual

KT-7020
CIRCUIT DESCRIPTION
Noise detector and electric field strength detec-
tor circuits
1. Noise detector
This circuits detects the presence/absence of interfer-
ence from adjacent stations, etc., and applies the
microprocessor with the Noise present (5V)} or absent
(OV) signal. The detection output is extracted from AF
OUT of IC5 (LA1231N) in the daughter (2), and only the
noise component is amplified by 120kHz (center fre-
quency) tuning amp IC6 (BA401). The output is regulat-
ed by D050 and D511, and the comparator in !C7 outputs
“H" = 14V ("L": —12V) when the noise DC voltage
attains about 1.4V. This output is 5V/OV converted by
D52, R127 and R128, and applied to the microproces-
SOF port.
2. Field strength detector
The S meter voltage from IC5 (LA1231N) in DT2 is
detected and, when the field strength exceeds 70 dB
with respect to the ANT input voltage, the IC7 output
goes "H” = 14V. This is 5V/OV converter and supplied
to the microprocessor.
I +3118¥)
3h
To Microprocessor
Sv: NARROW
Ov: WIDE
+8 (15V)
DT2 S-METER
R128 27K
(x13)
1.63¥ To Microprocessor
‘SV: DIRECT
OV: DISTANCE
—B (-t3v)
KT-7020
CIRCUIT DESCRIPTION
Active Reception Circuit
START
Tuning operation start
—
YesT Auto mode
RF SELECTOR
DISTANCE
IF BAND
NARROW
Auto-scanning
eS Up/Down
Radio wave
detected?
Manual mode
Preset tuning
RF SELECTOR
DISTANCE
IF BAND
NARROW
| Tuning start | start
Tuning operation stop
Yes
Auto~scanning
stop
Field strength
measurement
Yes
RF SELECTOR
DIRECT
Interference
detection
Interference
present?
IF BAND
WIDE
Tunung operation End
RF_SELECTOR
DISTANCE
Present
IF BAND
NARROW
* If the ANT Input Is very small (less than 10dByF)
the Forced Narrow mode is activated regardless
of the presence or absence of interference.

Kenwood KT-7020 Specifications

FM Tuner Section

tuning frequency range	87.5 MHz - 108 MHz
usable sensitivity (MONO)	0.95 µV/10.8 dB
total harmonic distortion (MONO)	0.007%
signal to noise ratio (MONO)	92 dB
stereo separation (1 kHz)	65 dB
capture ratio	1.0 dB (WIDE)
alternate channel selectivity (+400 kHz)	60 dB (WIDE)
image rejection ratio (at 98 MHz)	82 dB
IF rejection ratio (at 98 MHz)	110 dB
spurious rejection ratio (at 98 MHz)	105 dB
AM suppression ratio	76 dB
frequency response	20 Hz - 15 kHz, +0.5 dB, -0.5 dB
output level/impedance	0.6 V/3.3 kΩ

AM Tuner Section

tuning frequency range	531 kHz - 1, 602 kHz
usable sensitivity	10 µV (350 µV/m)
signal to noise ratio	55 dB
total harmonic distortion	0.25%
image rejection ratio (Loop)	40 dB
selectivity	30 dB
output level/impedance	0.18 V/3.3 kΩ

General

power consumption	20 W
dimensions (W x H x D)	440 mm x 98 mm x 318 mm
weight	4.3 kg