Kenwood TS-990S Service Manual

TS-990S
20
CIRCUIT DESCRIPTION
Band BPF selection classifi cation IF switching frequency criteria
IF frequency
TX IF Sub RX IF
135kHz f

522kHz f

522kHz
73M
73M SRX-2
BC 0.522

f

1.705MHz 0.522

f

1.705MHz 73M SRX-2
1.8MHz 1.705

f

2.5MHz
1.705

f

2.1MHz 11M SRX-1
2.1

f

3.4MHz 73M SRX-2
3.5MHz 2.5

f

4.1MHz
3.4

f

4.1MHz 11M SRX-1
5MHz 4.1

f

6.9MHz 4.1

f

6.9MHz 73M SRX-2
7MHz 6.9

f

7.5MHz 6.9

f

7.5MHz 11M SRX-1
10MHz
7.5

f

10.5MHz 7.5

f

10.5MHz 73M SRX-2
10.5

f

13.9MHz 10.5

f

13.9MHz 73M SRX-2
14MHz 13.9

f

14.5MHz 13.9

f

14.5MHz 11M SRX-1
18MHz
14.5

f

21.5MHz
14.5

f

20.9MHz 73M SRX-2
21MHz
20.9

f

21.5MHz 11M SRX-1
28MHz 21.5

f

30.0MHz 21.5

f

30.0MHz 73M SRX-2
50MHz (TX) 49.0

f

54.0MHz 49.0

f

54.0MHz - -
50MHz (RX) 30.0

f

60.0MHz 30.0

f

60.0MHz - 73M SRX-2
Table 13 Criteria for selecting the SRX-1 path or SRX-2 path
4-3. 2nd IF Frequency (10.695MHz/11.374MHz)
The 2nd IF signal passing through the SRX-1 or SRX-2
path is amplifi ed by approximately 16 dB in the 2nd IF am-
plifi er 1 (Q481), and is then distributed into 2 paths, the NB
circuit and the blanking circuit (D481 to D484). Blanking is
implemented by D481 to D484 for the signal from the NB cir-
cuit. The 2nd IF signal then passes through the IF fi lter. One
of 5 fi lters is selected, depending on the frequency and the
mode. (Refer to Table 14.)
The 2nd IF signal passing through the IF fi lter is input to
the AGC amplifi er (Q491). AGC voltage output from the DSP
is input to the gate2 terminal of Q491, and the gain of AGC
amplifier is controlled. Next, the signal is amplified to ap-
proximately 20 dB by the 2nd IF amplifi er (Q494 and Q495)
and passes through the ATT diode (D501). The voltage
determined in the adjustment mode is applied to D501, and
the difference of the total gains between SRX-1 and SRX-2
paths have adjusted.
IF
frequency
IF fi lter
Mode
FM AM SSB FSK CW
10.695MHz
15kHz
6kHz
2.7kHz
11.374MHz
2.7kHz
500Hz
Table 14 Selecting the IF fi lter
Fig. 18 2nd IF frequency (10.695MHz/11.374MHz)
Q481
Sub 2nd IF
AMP1
IF input
(11.374MHz)
IF input
(10.695MHz)
D481~484
Noise blanking
D487
D495
XF481
10.695M 15k
XF482
10.695M 6k
D490
TX
D496
XF484
10.695M 2.7k
D488
D503
XF485
D491
D505
TX
D494
D504
D492
D506
11.374M 2.7k
D489
XF486
11.374M 500
D493
Q491
Sub AGC
AMP
SAGCV
Q494,495
Sub 2nd IF
AMP2
D501
ATT
SIFGC
IF output
(10.695MHz/11.374MHz)

Kenwood TS-990S Specifications

General

Receiver Type	Triple Conversion Superheterodyne
Antenna Tuner	Built-in automatic antenna tuner
DSP	Yes
IF DSP	Yes
Modes	SSB, CW, AM, FM
Display	7-inch TFT color LCD
Weight	25 kg (55.1 lbs)
Antenna Connectors	SO-239
Power Supply	13.8V DC