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The signal is applied to the relay (FILTER unit; RL7211) which is controlled by the band control IC (MAIN unit; IC3602) as the “L16M” signal via the buffer amplifier (MAIN unit; IC1301, pin 17). The signal passes through the low- pass filter (FILTER unit;
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The signal is applied to the relay (FILTER unit; RL7241) which is controlled by the band control IC (MAIN unit; IC3602) as the “L22M” signal via the buffer amplifier (MAIN unit; IC1301, pin 18). The signal passes through the low- pass filter (FILTER unit; L7245, L7246, L7248,
The filtered signal is applied to the antenna connector after being passed through the RL7301 and J7311.
The ALC (Automatic Level Control) circuit controls the gain of IF amplifiers in order for the transceiver to output a constant RF power set by the [RF PWR] control even when the supplied voltage shifts, etc.
The RF power level is detected at the power detector circuit (Filter unit; D7271) to be converted into DC voltage and applied to the MAIN unit as the FOR signal.
The FOR signal is applied to the comparator (IC1201, pin 2). The “POCV” signal, controlled by the [RF PWR] control via the I/O expander (IC3606, pin 5), is also applied to the other input (pin 3) for reference. The compared signal is output from pin 1 and applied to the IF amplifier in the MAIN (Q801) unit to control amplifying gain.
When the FOR signal exceeds the POCV voltage, ALC bias voltage from the comparator controls the IF amplifiers. This adjusts the output power to a specified level from the [RF PWR] control until the FOR and POCV voltages are equal- ized.
The APC (Automatic Power Control) circuit protects the power amplifiers on the PA unit from high SWR and excessive current.
•SWR APC CIRCUIT (FILTER AND MAIN UNITS)
The reflected wave signal appears and increases on the antenna connector. When the antenna is mismatched, D7272 of the power detector circuit (D7271, D7272, L7272) in the FILTER unit detects the signal and applies it to the ALC amplifier (IC1201, pin 9) in the MAIN unit as “REF” sig- nal. The output signal decreases the bias voltage of the RF APC amplifier to reduce the output power.
•CURRENT APC CIRCUIT (FILTER AND MAIN UNITS)
The power transistor current is detected from the different voltage between both terminals of a 0.012 Ω resistor (R6651) on the PA board. The detected voltage is applied to the differential amplifier (IC6501). When the current of the final transistors is more than 30 A, the detected voltage is applied to the APC amplifier controller (IC1201) in the MAIN unit to reduce the
The output of ALC amplifier (IC1201, pin 12) is applied to the CPU (IC3303, pin 97) as “RFML” signal to indicate the transmit power level on the display.
For antenna current meter indication, the “ANTM” signal from the optional
The micorphone audio signals can be monitored to check voice characteristics.
A portion of the transmit IF signal from the DSP IC (IC301) is mixed with a 12 kHz LO signal to demodulate into the AF signals. The demodulated signals are
The “MONI” signal from the DSP unit is amplified at the AF amplifier (MAIN unit; IC1603, pin 2), and then applied to the VCA amplifier to control the AF volume (pin 7). The amplified signal passes through to the AF mute circuit (MAIN unit; IC1602, pins 1, 7) which is controlled by the CPU via the expander IC (MAIN unit; IC3603) as the “AFMS” signal. The AF signal is applied to the AF power amplifier circuit (MAIN unit; IC1601, pin 1) to drive a speaker.
•ALC CIRCUIT
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| 8 | ALC | 9 |
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