Circuit Description - HYT TM-610 Service Manual

Circuit Description

1. Frequency Configuration
The receiver utilizes double conversion superheterodyne. The first IF is 49.95MHz and the second is
450KHz. The first local oscillator signal is supplied by the PLL circuit; and the second (50.4MHz) is
generated from the frequency tripling of TCXO (16.8MHz). The PLL circuit generates the frequencies
required for transmission. (See figure 1).
Frequency Range VHF: 136MHz— 174MHz
UHF: 400MHz— 470MHz
2. Receiver Circuit
The receiver circuit is shown as figure 1.
2.1 High Frequency Bandpass Amplifier Circuit
It consists of BPF, RF amplifier (Q111) and BPF (D110 and D111). The range of bandpass frequency is
the frequency range of the radio itself. The signal is filtered by the BPF to eliminate unwanted signals
before going to the first mixer.
2.2 First Mixer
The signal from BPF is mixed with the first local oscillator signal from PLL circuit at the first mixer (D112)
to become a 49.95MHz first IF signal. The first IF signal is then fed through the crystal filter (IF200) to
further remove spurious signals.
450MHz— 500MHz
470MHz— 520MHz
350MHz— 400MHz
440MHz— 470MHz
Figure 1 Receiver Circuit
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TM-610 Service Manual