Motorola SSETM 5000 service manual Transmitting, Rx Lna

Theory of Operation: Mode of Operation 2-3

2.2.2Transmitting

When the radio is transmitting, microphone audio is passed through gain stages to the CODEC, where the signal is digitized (see Figure 2-3). The CODEC passes digital data to the DSP, where pre- emphasis and low-pass (splatter) filtering are done. The DSP passes this signal to a digital/analog converter (DAC), where it is reconverted into an analog signal and scaled for application to the voltage-controlled oscillator as a modulation signal.

		Reference			TX	TX Driver	Power
						Amplifier	Module
		Oscillator			VCOBIC Buffer	U102	Q107	Directional
								Coupler
		Y200		Loop	VCO 1			U101
			FracN	Filter
							D101
					VCO 2
TX_SSI from	3		MOD	Note:
VOCON Board			IN	This UHF range has 2 VCOs ￿
	DAC	LPF		(1 TX, 1 RX)
	U203	FL200					PCIC
							U104

Serial EE

PROM

U4

	ABACUS III U500
RX_SSI to	3
VOCON Board	Crystal		Preselector	RX LNA	Preselector
		Mixer
	Filter		Filter		Filter

Dual

Antenna

Switch

To

Remote

Port

To

Harmonic Antenna

Filter

Sample	2ND
Clk	LO

MAEPF-27530-A

Figure 2-3. Transceiver (UHF Range) Block Diagram (Power and Control Omitted)

Transmitted signaling information is applied to the DSP from the microcontrol unit, where it is coded, and passed to the DAC, which handles it the same as a voice signal. The DAC output connects to the synthesizer modulation input. A modulated carrier is provided to the transmitter power amplifier, which transmits the signal under dynamic power control.

6881094C12-A November 11, 2004