2Nd If Frequency; Criteria For Selecting The Srx-1 Path Or Srx-2 Path; Selecting The If Filter - Kenwood TS-990S Service Manual

TS-990S
Band
135kHz
BC
1.8MHz
3.5MHz
5MHz
7MHz
10MHz
14MHz
18MHz
21MHz
28MHz
50MHz (TX)
50MHz (RX)
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
Q481
IF input
Sub 2nd IF AMP 1
(11.374MHz)
IF input
(10.695MHz)
20
CIRCUIT DESCRIPTION
BPF selection classifi cation IF switching frequency criteria
f  522kHz
0.522  f  1.705MHz
1.705  f  2.5MHz
2.5  f  4.1MHz
4.1  f  6.9MHz
6.9  f  7.5MHz
7.5  f  10.5MHz
10.5  f  13.9MHz
13.9  f  14.5MHz
14.5  f  21.5MHz
21.5  f  30.0MHz
49.0  f  54.0MHz
30.0  f  60.0MHz
Table 13 Criteria for selecting the SRX-1 path or SRX-2 path
D481~484
D487
Noise blanking
10.695M 15k
D495 D490
TX
D496 10.695M 6k
D488
10.695M 2.7k
D503
11.374M 2.7k
D489
11.374M 500
Fig. 18 2nd IF frequency (10.695MHz/11.374MHz)
f  522kHz
0.522  f  1.705MHz
1.705  f  2.1MHz
2.1  f  3.4MHz
3.4  f  4.1MHz
4.1  f  6.9MHz
6.9  f  7.5MHz
7.5  f  10.5MHz
10.5  f  13.9MHz
13.9  f  14.5MHz
14.5  f  20.9MHz
20.9  f  21.5MHz
21.5  f  30.0MHz
49.0  f  54.0MHz
30.0  f  60.0MHz
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
IF fi lter
frequency
15kHz
10.695MHz 6kHz
2.7kHz
2.7kHz
11.374MHz
500Hz
Table 14 Selecting the IF fi lter
XF481
Q491
D494
Sub AGC AMP
XF482
D491 D504
SAGCV
TX
D505
XF484
D492
XF485
D506
XF486
D493
IF frequency
TX IF Sub RX IF
73M
73M
11M
73M
11M
73M
73M 11M
73M
73M
11M
73M
11M
73M
-
- 73M
Mode
FM AM SSB FSK
D501
Q494,495
ATT
Sub 2nd IF AMP 2
IF output
(10.695MHz/11.374MHz)
SIFGC
SRX-2
SRX-2
SRX-1
SRX-2
SRX-1
SRX-2
SRX-1
SRX-2
SRX-2
SRX-1
SRX-2
SRX-1
SRX-2
-
SRX-2
CW