Qual Tron QTI-EMIDS User Manual Table of Contents
Qual-Tron, Inc. Users Manual Table of Contents
Users Manual Table of Contents
THEORY OF OPERATION POWER AMPLIFIER ASSEMBLY Driver Amplifier The driver amplifier section provides the following function. * Amplifies the output signal of the synthesizer. * Matches the low impedance of the power amplifier. * Provides some attenuation of harmonics. Power Amplifier The final power amplifier further amplifies this signal to the specified output level. Low Pass Filter The low pass filter provides the following functions: * Attenuates harmonics by approximately 50 dBm. * Matches the final power amplifier to 50 Ohms. Power Supply The power supply section provides a means of switching DC power to the final stage of the Power amplifier. SYNTHESIZER LO ASSEMBLY Crystal Oscillator A fundamental frequency crystal oscillator is operated in a Colpitts temperature-compensated circuit to give a stability of (2.5 PPM over the operating temperature range. The 12.8 MHz output of the TCVCXO drives the PLL chip. The PLL chip divides this frequency, to establish a reference frequency. This frequency is the reference (frequency) for phase comparison used internally in the chip as well as providing the channel spacing. The low frequency component of the modulating signal is used to modulate of the TCVCXO, for improved DC response. Voltage controlled Oscillator "VCO" The VCO operates at the output frequency and is controlled by applying a voltage to the voltage variable capacitor. The oscillator is tuned to the center of the operating frequency range so the voltage on the capacitor is compatible with the output range of the low pass filter. Phase Locked Loop "PLL" The PLL compares the VCO frequency, divided by the dual-modulus divider and internal dividers, to the reference frequency and outputs a series of correction pulses to the low pass filter to correct the VCO frequency. Dual Modulus Pre-Scalar & Buffer Dual Modulus operation will not be described here, since operation of this circuit is explained in great detail in common technical literature. A simplified explanation of dual modulus circuit operation is that it is an additional frequency divider used by the PLL. The buffer provides isolation to prevent switching spikes from getting back into the VCO and erroneously modulating the output frequency. Modulation Filter The modulation signal is passed through an active filter which attenuates all audio signals above the cutoff frequency, resulting in an improved signal to noise ratio. Modulation Attenuation Circuit The Modulation Attenuation Circuit consists of several resistors that may be switched in and out of the circuit to control the modulation level across the operating bandwidth of the Transmitter. Encoder Microcontroller The microcontroller includes Eprom, EEprom, Ram and various peripheral devices to accomplish the task required of the encoder. Additional Support Circuitry The following are some of the support circuits associated with the encoder: * Sensor Interface circuit. * Power Supply circuit. * User interface circuit (Switches and Pushbutton). * External state of health timer. * Low Battery detection circuit * Low voltage reset circuit. * Serial communications circuit (RS-232).
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