Circuit Description - Icom IC-R100 Service Manual

SECTION 4 CIRCUIT DESCRIPTION
41 RF CIRCUITS
4-1-1 FILTER CIRCUIT (PLL UNIT)
The IC-R100 has 3 antenna connectors (J7, 98, J9) for a
super-wideband receiving range of 0.1 MHz to 1856.0
MHz. Received signals enter one of the 3 antenna
connectors depending on the receive frequency range.
(1) 0.1—50.0 MHz FILTER
RF signals from an antenna connector (J8) are distributed
to three separate filters through switching diodes (D10,
D12) for filter selection.
* 0.1000— 1.6290 MHz
After passing through a switching diode (D10) a
0.1000— 1.6290 MHz signal is applied to an attenuator
consisting of R64~R66. The attenuator prevents
distortion of very strong signals from medium wave
broadcasting stations. The signal is applied to FIL 1
(С1--С5, 11, 12) which forms a low-pass filter. The
filter circuit cuts off frequencies of 1.6290 MHz or higher.
The filtered signal passes through a switching diode
(D11).
• 1.6295--32.7495 MHz
After passing through a switching diode (012) a
1.6295--32.7495 MHz signal is applied to FIL 2 (C1—
C7, L1, L2) which forms a high-pass filter. The filter
circuit passes frequencies approx. 1.630 MHz or lower.
The signal is applied to FIL 3 (С1--5, 11, 12) which forms
a low-pass filter. The filter circuit cuts off approx. 32.75
MHz or higher. The filtered signal passes through a
switching diode (D14).
| 32.7500--49.9995 MHz
A 32.7500 MHz~49.9995 MHz signal is applied to FIL 2
through the switching diode (О12). The signal is applied
to FIL 4 (C1~C9, L1~L4) which forms a bandpass filter.
The bandpass filter passes signal within the frequency
range of 32.7500~50.0000 MHz. The filtered signal is
applied to the switching diode (D14).
е RF CIRCUITS
0,1--49,9995 MHz
0.1—1.8290 MHZ
1.6295--49.9995 MHz 1.6295 一 32.7495 MHz
(2) 50.0--905.0 MHz FILTER
No filter is installed in this frequency range. RF signals
enter an antenna connector (J7) and then are applied
to the RF relay circuit (RL2, RL3). The RF relay circuit
switches the signals to bypass through a preamplifier
(С2) ог be amplified at the preamplifier. The pre-
amplifier (IC2) provides 15 dB gain to attenuate ап IF
signal level at an attenuator circuit (Q16) when the
preamplifier circuit is turned ON.
(3) 905.0--1856.0 MHz FILTER
RF signals enter an antenna connector (J9) and then pass
through a switching diode (018). The signals are applied
to two separate high-pass filters for frequencies lower than
and higher than 1380.5 MHz. The filtered signals pass
through a switching diode (D21).
4-1-2 HF BAND CONVERTER CIRCUIT
(PLL UNIT)
The filtered signals entering at J8 are applied to a 1st
mixer circuit consisting of IC7, L29, L30 and then are
mixed with a 63.0 MHz 1st LO signal to produce a 63.1
~112.9995 MHz 1st IF signal corresponding to the
receive frequency range ої 0.17-49.9995 MHz.
The 63.0MHz 1st LO signal is generated by a local
oscillator (X1, Q1). X1 produces a 12.6 MHz reference
frequency. The reference frequency is multiplied by five
at LO amplifiers (Q6, Q15) for producing the 63.0 MHz
1st LO signal.
4-1-3 1GHz BAND CONVERTER CIRCUIT
(PLL UNIT)
The filtered signals entering at J9 are applied to a RF
amplifier (IC8) corresponding to a UHF band and then
applied to a 1st mixer circuit (IC9). IC9 is a DBM (Double
Balanced Mixer) The signals are mixed with a 475.5
905.0 MHz 1st LO signal to produce a 429.5— 905.0
MHz 1st IF signal corresponding to the receive frequency
range of 905.0— 1856.0 MHz. Тһе 475.5--905.0 MHz 1st
Lo signal is buffer-amplified at IC10 depending on the
receive frequencies. The signal is applied to the 1st
mixer circuit (IC9).
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1st LO signat
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