Motorola IC-T81E, IC-T81A DRIVE/POWER Amplifier Circuits RF Unit, APC Circuits RF Unit, MHz PA

(3) 440 MHz band

The signals from the limiter amplifier (RF unit; IC301) changes the reactance of a diode (VCO unit; D321) to mod- ulate the oscillated signal at the 440-VCO circuit (VCO unit; Q321, Q322, D321, D322, L322). The modulated signals are amplified at the buffer-amplifier (Q323) and the LO amplifier (Q823). The amplified signals are applied to the drive/power amplifier circuits for UHF band.

(4) 1200 MHz band

The signals from the limiter amplifier (RF unit: IC301) changes the reactance of a diode (VCO unit; D352) to mod- ulate the oscillated signal at the 1200-VCO circuit (VCO unit; Q350, D351, D352, L330). The modulated signals are ampli- fied at the buffer-ampifier (Q351). The amplified signals are applied to the doubler circuit (Q353), and then passed through the high-pass (C376–C380, L334, L335) and the low-pass (C381–C386, L336, L337) filters. The filtered sig- nals are amplified at the buffer-amplifier (Q354) and the LO amplifier (Q824). The amplified signals are applied to the drive/power amplifier circuits for SHF band.

The amplified signal is passed through the antenna switch- ing circuit (D101 and D102), low-pass filters and high-pass filters. The signal is applied to the antenna connector.

(3) 440 MHz PA

The signal from the LO amplifiers (Q823) is passed through the Tx/Rx switch (D804 and D805), and is amplified at the buffer amplifier (Q135) and the YGR amplifier (Q136). The amplified signal is applied to the driver amplifier (Q921), and is then amplified at the power amplifier (Q922) to obtain 5.0 W of RF power.

The amplified signal is passed through the antenna switch- ing circuit (D402 and D403), low-pass filters and high-pass filters. The low-pass filtered signal is applied to the antenna connector.

(4) 1200 MHz PA

The signal from the LO amplifiers (Q824) is passed through the Tx/Rx switch (D806 and D807), and is amplified at the buffer-amplifiers (Q131 and Q132) and the YGR amplifier (Q138). The amplified signal is applied to the driver ampli- fiers (Q921) to obtain 1.0 W of RF power.

4-2-3 DRIVE/POWER AMPLIFIER CIRCUITS (RF UNIT)

The amplifier circuit amplifies the VCO oscillating signal to the output power level.

(1) 50 MHz PA

The signal from the LO amplifiers (Q821) is amplified at the buffer-amplifier (Q133) and the YGR amplifier (Q134). The amplified signal is applied to the driver amplifiers (Q921), and is then amplified at the power amplifier (Q922) to obtain 5.0 W of RF power.

The amplified signal is passed through the antenna switch- ing circuit (D101 and D102) and low-pass filters, and is then applied to the antenna connector.

(2) 144 MHz PA

The signal from the LO amplifiers (Q822) is passed through the Tx/Rx switch (D802 and D803), and is amplified at the buffer-amplifier (Q133) and the YGR amplifier (Q134). The amplified signal is applied to the driver amplifiers (Q921), and is then amplified at the power amplifier (Q922) to obtain 5.0 W of RF power.

The amplified signal is passed through the antenna switch- ing circuit (D51 and D52), low-pass filter and high-pass fil- ters. The high-pass filtered signal is applied to the antenna connector.

Collector voltages for the drive amplifier (Q921) and control voltage for the power amplifier (Q922) and YGR amplifier (Q138) are controlled by the APC circuit to protect the power module from a mismatched condition as well as to stabilize the output power.

4-2-4 APC CIRCUITS (RF UNIT)

The APC circuit protects the power amplifier from a mis- matched output load and stabilizes the output power. The APC circuit is designed to use VHF, UHF and SHF bands commonly.

• APC CONTROL CIRCUIT APC SENSOR CIRCUIT

VCC	R911
TXC				YGR
	Q912	1200 MHz		amp.
		RF transmit		Q138
	Q913	signal
	430 MHz		YGR
	RF transmit		amp.
	signal		Q135

50, 144 MHz

RF transmit YGR

signalamp.

	D/A CONVERTER		2 –		Q134
				1	VGGC
+3C	IC5 (LOGIC unit)	6	PSET 3 IC901
			+
			Differential
			amplifier

Drive		Power		to the antenna
amp.		amp.
	Q921		Q922

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