12
TK-2118
TK-260
:K, K2
Item
Rating
Nominal center frequency
51.650MHz
Pass band width
±
5.0kHz or more at 3dB
35dB stop band width
±
20.0kHz or less
Ripple
1.0dB or less
Insertion loss
4.0dB or less
Guaranteed attenuation
70dB or more at fo-910kHz
Terminal impedance
400
Ω
/ 2.5PF
Item
Rating
Nominal center frequency
450kHz
6dB band width
±
6.0kHz or more
50dB band width
±
12.5kHz or less
Ripple
2.0dB or less at fo
±
4kHz
Insertion loss
6.0dB or less
Guaranteed attenuation
35.0dB or more at fo
±
100kHz
Terminal impedance
2.0 k
Ω
XF1:L71-0585-05
CF1:L72-0958-05
2) First Mixer
The signal from the RF amplifier is heterodyned with the
first local oscillator signal from the PLL frequency synthesizer
circuit at the first mixer (Q12) to create a 51.65MHz first
intermediate frequency (1st IF) signal. The first IF signal is
then fed through two monolithic crystal filters (MCFs : XF1) to
further remove spurious signals.
3) IF amplifier
The first IF signal is amplified by Q6, and then enters IC2
(FM processing IC). The signal is heterodyned again with a
second local oscillator signal within IC2 to create a 450kHz
second IF signal. The second IF signal is then fed through a
450kHz ceramic filter (CF1) to further eliminate unwanted
signals before it is amplified and FM detected in IC2.
4) AF amplifier
The recovered AF signal obtained from IC2 is amplified by
IC306 (1/4), filtered by the IC306 low-pass filter (2/4) and
IC306 high-pass filter (3/4) and (4/4), and de-emphasized by
R404 and C363. The AF signal is then passed through a
WIDE/NARROW switch (Q316). The processed AF signal
passes through an AF volume control and is amplified to a
sufficient level to drive a loud speaker by an AF power
amplifier (IC309).
CIRCUIT DESCRIPTION /
电路说明
2) 第一混频器
来自射频放大器的信号与来自锁相环频率合成器电路的第一
本振信号在第一混频器 (Q12) 处混频并生成51.65MHz的第一中
频 (1st IF) 信号。第一中频信号通过两个单片晶体滤波器 (MCFs:
XF1) 进一步消除邻道的杂波信号。
3) 中频放大器
第一中频信号通过Q 6 放大，然后进入芯片I C 2 ( 调频处理芯
片)。信号在IC2中与第二本振信号再次混频生成一个450kHz的
第二中频信号。在芯片I C 2 中第二本振信号被放大和鉴频之前,
通过一个450kHz陶瓷滤波器 (CF1) 滤除无用杂散信号。
项目
额定值
标称中心频率
51.650MHz
通频带宽
±
5.0kHz或更大 在3dB内
35dB止频带宽
±
20.0kHz或更小
脉动
1.0dB或更小
插入损耗
4.0dB或更小
保证衰减
70dB或更大
在fo-910kHz
终端阻抗
400
Ω
/ 2.5PF
XF1：L71-0585-05
CF1：L72-0958-05
项目
额定值
标称中心频率
450MHz
6dB频带宽度
±
6.0kHz或更大
50dB频带宽度
±
12.5kHz或更小
脉动
2.0dB或更小
插入损耗
6.0dB或更小
保证衰减
35.0dB或更大
终端阻抗
2.0k
Ω
/ 3PF
4) 音频放大器
在IC2中鉴频解调出的音频信号通过IC306 (1/4) 放大，通过
IC306低通滤波器 (2/4) 以及IC306高通滤波器 (3/4) 和 (4/4) 滤
波，并且通过R 4 0 4 和C 3 6 3 去加重。然后音频信号通过一个宽/
窄转换开关 (Q316)。经过处理的音频信号通过音量控制电路再
经过音频功率放大器 (IC309) 放大后、驱动扬声器。
