Kenwood TK-2107G Service Manual

TK-2107G102-2. First mixerThe signal from the RF amplifier is heterodyned with thefirst local oscillator signal from the PLL frequency synthe-sizer circuit at the first mixer (Q202) to create a 38.85MHzfirst intermediate frequency (1st IF) signal. The first IF signalis then fed through two monolithic crystal filters (MCFs :XF200) to further remove spurious signals.2-3. IF amplifi erThe first IF signal is amplified by Q201, and then entersIC200 (FM processing IC). The signal is heterodyned againwith a second local oscillator signal within IC200 to createa 450kHz second IF signal. The second IF signal is then fedthrough a 450kHz ceramic filter (CF200) to further eliminateunwanted signals before it is amplified and FM detected inIC200.XF200: L71-0522-05Item RatingNominal center frequency 38.850MHzPass band width ±5.0kHz or more at 3dB40dB stop band width ±20.0kHz or lessRipple 1.0dB or lessInsertion loss 4.0dB or lessGuaranteed attenuation 80dB or more at fo–910kHzTerminal impedance 610Ω / 3pFCF200: L72-0958-05Item RatingNominal center frequency 450kHz6dB band width ±6.0kHz or more50dB band width ±12.5kHz or lessRipple 2.0dB or less at fo ±4kHzInsertion loss 6.0dB or lessGuaranteed attenuation 35.0dB or more at fo ±100kHzTerminal impedance 2.0kΩ2-4. AF amplifierThe recovered AF signal obtained from IC200 is amplifiedby IC300 (1/4), filtered by the IC300 low-pass filter (2/4) andIC300 high-pass filter (3/4) and (4/4), and de-emphasizedby R303 and C306. The AF signal is then passed through aWIDE/NARROW switch (Q303). The processed AF signalpasses through an AF volume control and is amplified to asufficient level to drive a loud speaker by an AF power am-plifier (IC302).2-2. 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 ( Q202) 处混频并生成 38.85M H z 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: XF200) 进一步消除邻道的杂波信号。2-3. 中频放大器第一中频信号通过 Q201 放大，然后进入芯片 I C200( 调频处理芯片 )。信号在 IC200 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 IC200 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 (CF200) 滤除无用杂散信号。XF200: L71-0522-05项目额定值标称中心频率 38.850MHz通频带宽 ±5.0kHz 或更大在 3dB 内40dB 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 80dB 或更大终端阻抗 610Ω/3pFCF200: L72-0958-05项目额定值标称中心频率 450kHz6dB 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 2.0kΩ2-4. 音频放大器在 I C200 中鉴频解调出的音频信号通过 I C300(1/4) 放大，通过 I C300 低通滤波器 (2/4) 以及 I C300 高通滤波器 (3/4)和 (4/4) 滤波，并且通过 R303 和 C306 去加重。然后音频信号通过一个宽 / 窄转换开关 ( Q303)。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 ( I C302) 放大后、驱动扬声器。CIRCUIT DESCRIPTION / 电路说明