From The 2Nd If To The Mrif Output; Preselector Circuit; Selecting An If Fi Lter; Preselector Operation Frequency - Kenwood TS-990S Service Manual

TS-990S
IF frequency
8.248MHz
*1 : manually selectable

3-3. From the 2nd IF to the MRIF output

In FM mode, the signal passing through D30 is applied to
the FM IC (IC9) via D31. In modes other than FM, the signal
passing through D30 is input to the AM/SSB/CW/FSK/PSK
mode mixer (D32 and D33) via D31 (Refer to Fig. 7).
In FM mode, the FM signal is mixed with the MLO2
(7.793MHz) output in the FM wave detecting IC and con-
verted into the 2nd IF (455kHz). The 2nd IF signal passes
through the ceramic filters (CF1: 9kHz (narrow) and CF2:
IF input
(8.248MHz)

3-4. Preselector circuit

This transceiver has a preselector on the PRESEL unit
(X42-343 B/10). This function can be turned ON and OFF
with a panel switch.
The preselector forms narrow band-pass fi lters in which
inductors and capacitors are switched with relays for respec-
tive amateur bands. (Refer to Table 7.)
The fi lters cause an insertion loss of about 10 dB by the
band if the preselector function is used. This insertion loss is
compensated with the combined use of the variable attenua-
tor (ATT) in the PRESEL unit and the preselector AMP (Q10
and Q11) in the RX unit (X55-313 A/2).
12
CIRCUIT DESCRIPTION
IF fi lter
FM
15kHz
6kHz
2.7kHz
500Hz
270Hz
Table 6 Selecting an IF fi lter
D31
Switching
FM
IC9
FM IC
CF1
CF2
SSB, CW, AM,
FSK, PSK
D32,D33
2rd mixer
Fig. 7 From the 2nd IF to the MRIF output
Mode
AM SSB
*1
*1
*1
*1
12kHz (wide)), is demodulated into audio signals and ampli-
fi ed by the FM AF AMP (IC12).
Signals other than FM mode are mixed in the AM/SSB/
CW/FSK/PSK mode mixer (D32 and D33) with the MLO2
(8.224MHz) output, converted to the 2nd IF (24kHz), and
amplifi ed by the IF AMP (IC10).
These signals are output to the DSP unit (X53-453)
through the MRIF connector (CN137).
IC12
FM AF AMP FM
(AF)
455kHz BPF
BW: 9kHz (Narrow)
455kHz BPF
BW: 12kHz (Wide)
SSB, CW, AM,
FSK, PSK
24kHz
(24kHz)
IC10
IF AMP
Band
1.8MHz
3.5MHz
5MHz
7MHz
10MHz
14MHz
18MHz
21MHz
24.9MHz
28MHz
Table 7 Preselector operation frequency
FSK CW
*1 *1
*1 *1
IC11
Multiplexer
MRIF
CN137

Preselector operation frequency

1.7975~2.00499MHz
3.4925~4.01749MHz
5.2400~5.46999MHz
6.9800~7.33999MHz
9.9800~10.17999MHz
13.9500~14.44999MHz
18.0180~18.26799MHz
20.9000~21.69999MHz
24.7900~25.18999MHz
27.9000~29.89999MHz