Icom IC-F7000 service manual Circuit Description, Receiver Circuits, DSP Unit

SECTION 4 CIRCUIT DESCRIPTION

4-1 RECEIVER CIRCUITS

4-1-1 RF FILTER CIRCUIT (PLL AND MAIN UNITS)

Received signals from the antenna connector are applied to the transmit/receive switching and protection relay (PLL unit; RL7301) which is controlled by the CPU via the “TRXS” line. The signals pass through the 30 MHz cut-off low-pass filter (PLL unit; L7321, C7321–C7323, C7325), and then applied to the MAIN unit via the J7321.

The signals pass through the 1.6 MHz cut off high-pass fil- ter (MAIN unit; L51–L54, L57, C54, C56, C57, C59, C61–C64, C69) and transmit/receive switch (D54), and are then applied to one of the bandpass filters (including one low-pass filter for below 2.0 MHz). These filters are selected by the filter control signals (B0–B8) as described in the table below.

4-1-2 1ST MIXER AND IF CIRCUITS (MAIN UNIT)

The 1st mixer circuit converts the received signals into a fixed frequency, 64.445 kHz 1st IF signal using PLL output frequency. By changing the PLL frequency, only the desired frequency is picked up at the 64.445 kHz bandpass filter (FI201) at the next stage.

The IF amplifier (Q203) and resonator circuits are designed between the filter pair. The PLL output signal (1LO) enters the MAIN unit via the J601 and is amplified at the 1st LO amplifier (Q601). The amplified signal is passed through the

100MHz cut-off low-pass filter (L602–L604, C602, C604–C607, C609) to suppress harmonic components, and then applied to the 1st mixer circuit (Q201, Q202, Q204, Q205).

4-1-3 2ND MIXER AND IF CIRCUITS (MAIN UNIT)

The filtered signals are applied to the pre-amplifier (MAIN unit; Q102, Q103), and then passed through the 33 MHz cut-off low-pass filter (L202, L203, C202–C206). The filtered

Frequency (MHz)	LPF ctrl signal	BPF ctrl signal
0.5–1.9999	L1M	B0
2.0–2.4999		B1
2.5–2.9999	L2M
3.0–3.4999		B2
3.5–4.9999	L4M
5.0–5.4999		B3
5.5–6.9999	L6M
7.0–8.9999		B4
9.0–9.9999
10.0–13.9999	L12M	B5
14.0–14.9999		B6
15.0–17.9999
18.0–23.9999	L22M	B7
24.0–29.9999		B8

signals pass through the low-pass filter (MAIN unit; L202, L203, C202–C206), and are then applied to the 1st mixer circuit (Q201, Q202, Q204, Q205).

The 1st IF signal from the bandpass filter (FI201) is convert- ed again into a 455 kHz 2nd IF signal at the 2nd mixer cir- cuit (D303, L303, L304). The 2nd LO signal (2LO) from the PLL unit enters the MAIN unit via the J301 to be applied to the 2nd mixer circuit.

4-1-4 3RD MIXER AND IF CIRCUITS (MAIN UNIT)

The 2nd IF signal passes through the low-pass filter (L305, C308, C310, C311, C315), and is then applied to the IF amplifier (Q401) via the ceramic bandpass filter (FI401). The amplified signal passes through the other ceramic bandpass filter (FI402), and then applied to the 3rd mixer circuit via the IF amplifier (Q501). The 2nd IF signal is converted into a 12 kHz 3rd IF signal at the 3rd mixer circuit (IC501). The 3rd LO signal (3LO) from the PLL unit enters the MAIN unit via the J3601 to be applied to the 3rd mixer circuit.

• RECEIVER CONSTRUCTION

Antenna

						1st LO			2nd LO
	64						94 MHz		64 MHz
		0.5 1.9999 MHz
LPF				LPF				Crystal		Crystal	IF
					1st mixer			BPF	2nd mixer	BPF	amp.
PLL unit								FI201		FI401	Q401
						Q201			D303
				BPF
						Q202
			2 30 MHz			Q203
						Q204			3rd LO
									443 kHz

to transmit/receiver switch

DSP

UNIT

IF	LPF	IF	Crystal
amp.		amp.	BPF
IC1002		3rd mixer Q501	FI402
		IC501

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