Kenwood TK-940 service manual RF unit, If unit, MCF ANT AMP If System -AMPSP, Pll Mic Amp

CIRCUIT DESCRIPTION

I 1. Overview

This transceiver is an 800MHz-band (TK-9401, 9OOMHz-band (TK-941) EFJ LTRrM trunked-system- compatible FM transceiver that can be programmed to operate on both LTR and conventional systems.

2. Circuit Configuration by Frequency

The receiver I S a double-conversion superhet with a first intermediate frequency (IF) of 45.0375MHz (TK- 940), 39.0375MHz (TK-941)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 45.0375MHz (TK-940), 39.0375MHz (TK-941).

This is then mixed with the 44.5825MHz (TK-940), 38.5825MHz (TK-941) second local osclllator output t o produce the 455Hz 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 micro- phone. It is then amplified by TX amplifier and PA amplifier, and sent to the antenna.

I					CF
ANT TK-940		TK-941			455kHz
TX	806-825MHz	TX	896-902MHz
	851-870MHz		935-941MHz
RX	851-870MHz	RX	935-941MHz
			1st MIX	MCF
ANT	RF					AF
SW	AMP			'IF SYSTEM -AMPSP
A			45.0375MHz :TK-940		44.5825MHz :TK-940
			39.0375MHz :TK-941
I					38.5825MHz : TK-941
			805.9625-824.9625MHz.: TK-940
					PLL	MIC	MIC
		AMP	--			-AMP
	- TK-940			TK-941
			806-825MHz	896-902MHz
			851-870MHz	935-941MHz

Fig. 1 Frequency configuration

3.Receiving System

3-1. RF unit

An incoming RF signal from the antenna terminal

passes through the antenna switch (D19, D20, and D21 are off) and then the bandpass filter (L9). The

signal is ampliked by RF amplifier 024, and passes through the bandpass filter (L6) again. The resulting signal goes to the flrst mixer (021), where it is mixed with the first local oscillator signal output from the frequency synthesizer t o produce the first IF 45.0375MHz (TK-9401, 39.0375MHz (TK-941).

3-2. IF unit

The flrst IF s~gnalthen passes through a four-pole mono~thlccrystal flter (XFI The s~gnal1s ampllfled by flrst IF amplrf~er0 1 6 and goes to the second IF unlt

The second IF unit cons~stsof an IF system IC ( I C ~ ) and the second mlxer, second local osclllator, second IF fllter, and FlV detector, tC7 mlxes the slgnal Input to ~tw ~ t hthe 44 5825MHriiTK-940), 38 5825MHz (TK-

941)second local osclllator output #f the clystal osclilator (X2)to produce the second IF c' '55kk

The 455kHz slgnal then goes throug 55khL ce-

ramic filter CFI, is amplifl	5y the Ilm	ampllfler,
demodulated by the quac	re FM de	or (In the
same IC), and output to tht	elve audlo ,	l p l ~ f ~ e r