Icom IC-F50, IC-F51 service manual Other Circuits, Port Allocations, Compounder Circuit Main Unit

4-5 OTHER CIRCUITS

4-5-1 COMPOUNDER CIRCUIT (MAIN UNIT)

IC-F50/F51 have compounder circuit which can improve S/N ratio and become wide dynamic range to suppress the transmitting signal and to extend receiving signal. The circuit is composed of the base band IC (MAIN unit; IC10).

(1) IN CASE OF TRANSMITTING

The audio signals from the microphone are applied to the base band IC (IC10, pin 3) via microphone mute circuit (FRONT unit; IC406), microphone amplifier (IC407), etc. The signals are amplified at the amplifier section, and are then applied to the compressor circuit to compress the audio signals. The signals pass through (or bypass) scrambler section, and are then amplified at limiter amplifier section after being passed through the high-pass filter. The ampli- fied signals pass through the low-pass filter section, and are then applied to the modulation circuit (Q13, D16–D18) via the FM/PM switch (IC11), low-pass filter (IC5) and D/A con- verter (IC6).

(2) IN CASE OF RECEIVING

The demodulated AF signals from the IF IC are applied to the amplifier section of base band IC (IC10, pin 23), and then pass through the low-pass and high-pass filter section to suppress unwanted signals. The filtered signals pass through (or bypass) scrambler section, and are then applied to the expander circuit to expand AF signals. The signals pass through (or bypass) scrambler IC (IC14), and are then applied to the analog switch (IC13, pins 8, 11). The signals are applied to the base band IC’s amplifier section (IC10, pins 19, 20), and are then applied to the AF amplifier circuit.

•BASE BAND IC BLOCK DIAGRAM

4-6 PORT ALLOCATIONS

4-6-1 EXPANDER IC (FRONT UNIT; IC410)

Pin	Port	Description
number	name
4	LEDR	Outputs RX LED control signal.
		Low: Lights ON.
5	LEDT	Outputs TX LED control signal.
		Low: Lights ON.
6	LIGT	Outputs back light LED control signal.
		Low: Back light is ON.
		Outputs audio control signal.
7	AFON	Low: Outputs audio signals from
		speaker.
		• Outputs CTCSS/DTCS switching sig-
		nal when transmitting.
		High: Selected DTCS.
		• Outputs Min. VR switching signal
11	DUSE	when receiving.
		Low: Select Min VR.
		NOTE: Audio signals are prior to
		transmitting.
		Outputs microphone select signal.
12	MCON	High: While the internal microphone
		is used.
13	CSFT	Outputs shift signal for reference oscil-
		lator’s frequency.
		Outputs the internal speaker control
14	SPON	signal.
		High: The internal speaker is select-
		ed.

TXINO	4
TXIN	3	VR1
		(HPF)
	TXA1
RXINO	22
RXIN	23	VR3
		(HPF)
SDEC	21 RXA1
MTDT	10
MTCK	9

MDIR 14

MSCK 13

MDIO 11 Control

Register

MRDF 12

Com-

pressor

RX

LPF

MSK

BPF

Pre-

emphasis

TX/RX

HPF

MSK

Modulator

MSK

Demodulator

Limiter Splatter VR2 SMF 7 MOD

Scrambler/

De-scrambler

De-	Expander	VR4	18
emphasis

19

20 SIGNAL

RXA2

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