Qual Tron QTI-EMIDS User Manual Table of Contents

Qual-Tron, Inc. Users Manual Table of Contents

Users Manual Table of Contents

THEORY OF OPERATIONPOWER AMPLIFIER ASSEMBLYDriver AmplifierThe 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 AmplifierThe final power amplifier further amplifies this signal to thespecified output level.Low Pass FilterThe low pass filter provides the following functions:* Attenuates harmonics by approximately 50 dBm.* Matches the final power amplifier to 50 Ohms.Power SupplyThe power supply section provides a means of switching DC powerto the final stage of the Power amplifier.SYNTHESIZER LO ASSEMBLYCrystal OscillatorA fundamental frequency crystal oscillator is operated in aColpitts temperature-compensated circuit to give a stability of (2.5PPM over the operating temperature range. The 12.8 MHz output of theTCVCXO drives the PLL chip. The PLL chip divides this frequency, toestablish a reference frequency. This frequency is the reference(frequency) for phase comparison used internally in the chip as well asproviding the channel spacing. The low frequency component of themodulating signal is used to modulate of the TCVCXO, for improved DCresponse.Voltage controlled Oscillator "VCO"
The VCO operates at the output frequency and is controlled byapplying a voltage to the voltage variable capacitor. The oscillator istuned to the center of the operating frequency range so the voltage onthe capacitor is compatible with the output range of the low passfilter.Phase Locked Loop "PLL"The PLL compares the VCO frequency, divided by the dual-modulusdivider and internal dividers, to the reference frequency and outputs aseries of correction pulses to the low pass filter to correct the VCOfrequency.Dual Modulus Pre-Scalar & BufferDual Modulus operation will not be described here, sinceoperation of this circuit is explained in great detail in commontechnical literature.A simplified explanation of dual modulus circuit operation isthat it is an additional frequency divider used by the PLL. The bufferprovides isolation to prevent switching spikes from getting back intothe VCO and erroneously modulating the output frequency.Modulation FilterThe modulation signal is passed through an active filter whichattenuates all audio signals above the cutoff frequency, resulting inan improved signal to noise ratio.Modulation Attenuation CircuitThe Modulation Attenuation Circuit consists of several resistorsthat may be switched in and out of the circuit to control themodulation level across the operating bandwidth of the Transmitter.EncoderMicrocontrollerThe microcontroller includes Eprom, EEprom, Ram and variousperipheral devices to accomplish the task required of the encoder.Additional Support CircuitryThe following are some of the support circuits associated withthe 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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