Pacific Research Solutions RI-200 - Manual (Page 66)

Pacific Research Solutions RI-200 User Manual
Page 65
CIRCUIT DESCRIPTIONS
7.0 CIRCUIT DESCRIPTIONS
This section will cover the brief circuit description of the RI-200 repeater controller. Use the schematic on the following page
for additional reference. Only the basic function of each circuit is covered, theory of operation is not covered.
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The input of the RI-200 has an adjustable gain stage, U1-7. R3 is used to set the gain of this stage.
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U1-8 is a low pass filter with a cutoff frequency of 4500 Hz. This filter is used to reduce adjacent channel splatter.
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The output of the low pass filter goes to U9 where a high pass filter is located with a cutoff frequency of 300 Hz. This
filter can be turned on/off and is used to remove the receiver CTCSS tones.
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The output of the U9 high pass filter has a gain stage U1-14, with a gain of 2, used to return the audio level back to its
original level. U9 has half the audio voltage range of the rest of the circuits.
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The output of U1-14 goes to the cross point switch and U3-8 a de-emphasis filter.
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U3-8 is a de-emphasis filter used primarily for the DTMF decoder and telephone audio. Audio from this filter can also
be used for the transmitter.
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U4-7 is a low pass filter used to reject the voice band. The output of this filter feeds the CTCSS/DCS decoder.
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U9 is used for decoding CTCSS tones and DCS codes when the optional DCS function has been included in your
controller. U9 can also be used to encode CTCSS tones.
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U2-7 is the noise filter for the RI-200 squelch circuit.
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The noise filter then goes to the U3-1, a gain stage used to adjust the squelch level. The output of the gain stage goes to
the cross point switch, U6.
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The cross point switch U6, can connect any of the Y inputs to any of the X outputs. This switch is the primary method of
audio routing in the RI-200.
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The output of the Cross point switch goes to several places. The first is U4-14 a summing amplifier used to mix all audio
sources for the transmitter.
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The output of U4-14 feeds a digital potentiometer used to set the transmit modulation level.
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U5-7 is a buffer used to drive the repeater transmitter.
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Some of the audio in the controller will need pre-emphasis before the transmitter, U4-8. These audio’s include the
telephone, CTCSS/DCS, DTMF and sometimes the AUX audio.
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U5-8 is a buffer for the AUX audio output.
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The cross point switch is also used to control what audio goes to the U2-14 and U2-8 the AC to DC converter.
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The output of the AC to DC converter goes to an 8 bit analog to digital converter. This converter allows the
microprocessor to read the squelch noise level, receiver audio level and the telephone audio level.
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U3-14 is a limiter used to limit the maximum audio level sent to the telephone line.
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U5-1 and U3-7 make up the hybrid for the telephone interconnect. The digital potentiometer in this circuit is controlled
by the microprocessor to balance the telephone hybrid.
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The output of the hybrid goes to U3-1 a gain stage also used as the telephone AGC. The digital potentiometer in this
circuit is controlled by the microprocessor where the AGC is controlled.
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The output of the telephone hybrid is coupled to the telephone line using T1.
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K1 is used as the hook switch and for pulse dialing.
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ZNR1 is a fast acting semi-conductor used for lighting protection. R70 and R71 are used as fuses for the telephone.
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U7 is an opto coupler used as a ring detector. The output of the ring detector goes to the microprocessor.
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U19 is an output driver used to drive the hook relay and the status LEDs.
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U8 is the DTMF decoder and encoder. The DTMF encoder is also used as the tone generator for the CW messages. R34
is used to set the level of the DTMF encoder and tone generator.
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U20 is used mainly as a CTCSS and DCS encoder when the DCS option is installed.
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U13 is an 8K x 8 EEPROM. This device holds all macros, message data and telephone number tables.
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U14 is a 512 x 8 EEPROM, software watch dog and power monitor circuit. The system parameters are stored in this
device.
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U15 is the microprocessor, it also contains the program ROM and RAM.
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U17 is a digital buffer for the user digital input and output.
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U11 is the 5 volt power supply regulator. U12 is a minus 5 volt charge pump, which provides the minus 5 volt supply.