Circuit Description; 电路说明 - Kenwood TK-3148 Service Manual

Uhf fm transceiver

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Service manual (74 pages)

Table of Contents

TK-3148

1. Overview

This transceiver is UHF/FM portable transceiver designed

to operate in the frequency range of 350 to 390MHz (C).

2. Circuit Configuration by Frequency

The receiver is a double-conversion superheterodyne with

a first intermediate frequency (IF) of 44.85MHz and a second

IF of 455kHz. Incoming signals from the antenna are mixed

with the local signal from the PLL to produce the first IF of

44.85MHz.

This is then mixed with the 44.395MHz second local

oscillator output to produce the 455kHz second IF. This is

detected to give the demodulated signal.

The transmit signal frequency is generated by the PLL VCO,

and modulated by the signal from the microphone. It is then

amplified and sent to the antenna.

3. Receiver System

3-1. RF unit

An incoming RF signal from the antenna terminal is passed

through the antenna switch (D102, D103, D104 and D105 are

off) and then the bandpass filter (L215 and L217). High pass

filter HPF (L219) the 1st image response improve. And the

bandpass filter is adjusted by a variable capacitor. The input

voltage to the variable capacitor is regulated by the voltage

output from the D/A converter (IC307). The signal is amplified

by RF amplifier Q207, and passed through the bandpass filter

(L209, L210 and L211). The resulting signal is applied to the

first mixer (Q206), where it is mixed with the first local oscillator

signal output from the frequency synthesizer to produce the

first IF (44.85MHz).