Kenwood TS-830S Service Manual page 8

CIRCUIT DESCRIPTION
FILTER FILTER NOTCH
IF SHlFT
VBT 8.375MHz
Fig. 7 Frequency configuration
0 5 K M OSKHZ
CAR-2 8.375MHz 8.374MHz 8 . 3 7 4 M H ~
Fig. 8 VBT.IF SHlFT
2. VBT and I F SHlFT
VBT
(variable
'
b a n d w l d t h t u n i n g ) allows varylng the
bandwidth, operation of whlch is determlned by the 8 . 8 3
M H z and 4 5 5 kHz filters and by changing the output frequen-
cies of CAR-1 and CAR-2 simultaneously wi-th the VBT con-
trol Frequency organlzatlon of the VBT and IF SHlFT 1 s
shown In F ~ g u r e 7 Assuming that a signal centered at
1 4 0 0 1 5 MHz 1 s received wlthout l F shift or VBT, the VFO
output frequency is 5 . 5 0 1 5 MHz. CAR-1 8 8 3 1 5 kHz, and
the VCO output applied to the first mixer
IS
2 2 . 8 3 1 5 MHz.
The mlxer converts thls to a slgnal whose center frequency 1 s
8 8 3 0 M H z ( 2 2 8 3 1 5 M H z - 1 4 0 0 1 5 M H z = 8 8 3 0 MHz)
The slgnal frequency
I S
then converted t o 4 5 5 mHz by the se-
cond mlxer To help understand VBT operation, assume the
composite
bandwldth determlned by fllters XF1 and CF2 1 s
2 7 kHz In the normal (unshlfted) state of CAR-1 and -2
Frequency organ~zatlon to obtaln a speclflc bandwldth and IF
SHlFT 1 s described below
Example 1 (no IF shift)
[
Bandwidth
1 7 kHz
IF SHIFT 0 kHz
1
When the CAR-2 frequency 1 s reduced by 1 kHz uslng the
VBT control and a slgnal centered at 1 4 0 0 1 5 MHz
I S
recelv-
ed the CAR 1 and 2 frequencies are as follows
CAR-1
8 8 3 1 0 kHz
( =
8 8 3 1 5 k H z - 0 5 kHz*)
CAR-2 8 3 7 4 0 kHz (VBT control)
*
The system 1 s deslgned so that only half the amount of fre-
quency s h ~ f t applled to CAR 2
IS
applled t o CAR-1
Assume the recelved slgnal has a frequency spectrum exten-
ding over 1 4 0 0 1 5 MHz
5
1 3 5 ' k ~ z Slnce CAR-1 output 1 s
8 8 3 1 0 kHz. the VCO output frequency 1 s 2 2 8 3 1 0 M H z and,
therefore the frequency of the flrst IF slgnal
I S
8 8 2 9 5 kHz -t
1 3 5 kHz due to a shift of - 5 0 0 Hz
( 2 2 8 3 1 0 kHz- 1 4 0 0 1 5 kHz
=
8 8 2 9 5 kHz) Slnce the
freql~ency characterlstlc of the flrst IF fllter
I S
8 8 3 0
M H z k l 3 5 kHz as noted above frequency components are
cut In the lower slde band by 5 0 0 Hz more than In the nor-
mal state, as
illustrated
In Flg 8 ( 3 ) The second in-
termedlate frequency generated In the second mixer 1 s 4 5 5 5
kHz+l 3 5 kHz
BAND
1 . 5
3 . 5
7
I0
14
18
2 1
2 4 . 5
28
2 8 . 5
29
2 9 . 5
VCO M H z
-
1 0 . 3 3 - 1 0 . 8 3
1 2 . 3 3 - 1 2 . 8 3
15 8 3 - 1 6 . 3 3
1 8 . 8 3 - 19..33
2 2 . 8 3 - 2 3 . 3 3
2 6 . 8 3 - 2 7 . 3 3
2 9 . 8 3 - 3 0 . 3 3
3 3 . 3 3 - 3 3 . 8 3
3 6 . 8 3 - 3 7 33
37 33-37 83
3 7 . 8 3 - 3 8 . 3 3
3 8 . 3 3 - 3 8 . 8 3