TK-90
22
■
Receiving IF Filter
The 10.695MHz received signal converted at the second
mixer is amplified by the gain-controlled (AGC) second IF
amplifier (Q185). Q185 also functions as a noise blanker
gate. When blanking, the pulse voltage of the noise compo-
nent is added to the Q185 source terminal, and Q185 turns
OFF. It is then passed through a narrow band IF filter, elimi-
nating unnecessary signal components.
The default IF filters installed are for SSB (XF252: 2.4kHz
band) and AM (XF251: 6kHz band). On the TX-RX unit print
board, there is space for installing an optional filter. A CW
filter (YF-107C: 500Hz band) or SSB filter (KIF-2: 2.7kHz band)
can be installed as an optional filter.
Signals which are passed through the IF filter are amplified
with the IF amplifier (Q251), and are then input into the gain-
controlled (AGC) second IF amplifier (Q451 and Q455).
AM 6kHz
XF251
SSB/CW/FSK 2.4kHz
XF252
Optional filter
YF-107C, KIF-2
Q185
IF AMP
Q251
IF AMP
RX OUT
10.695MHz
IF IN
10.695MHz
AGC
BLNK
(NB gate)
CIRCUIT DESCRIPTION /
!
Item
Rating
Nominal center frequency
10.695MHz
Center frequency deviation
Within
±
150Hz at 6dB
Pass bandwidth and
2.2kHz or more at 6dB
Attenuation bandwidth
3.0kHz or less at 20dB
5.2kHz or less at 60dB
Ripple
2dB or less
Insertion loss
6dB or less
Guaranteed attenuation
80dB or more within
±
5~1000kHz
Terminal impedance
1.0k
Ω±
5% / 7pF
±
5%
Temperature range
–20
°
C~+70
°
C
Table 2
MCF (L71-0604-15): XF252
Item
Rating
Nominal center frequency
10.695MHz
Center frequency deviation
Within
±
100Hz (25
°
C, 6dB)
Pass bandwidth
500Hz or more (6dB)
Insertion loss
9dB
±
3dB
Ripple
2dB or less
Guaranteed attenuation
80dB or more within
±
2~1000kHz
Terminal impedance
800
Ω
/ 2pF
Table 3
MCF (YF-107C): CW optional filter
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