RF Pulser Controller

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To align a power amplifiers for optimum CW (pulse) operation this pulse controller was developed. Also it can be used when a dummyload with non adequate powerhandling is availabe (average powerhandling requirement is reduced by a factor of 2 to 3). It will control the exciter (transceiver), obtain a forward power voltage sample and output this voltage for measurement with a DC voltmeter. Input is a footswitch for continues pulse operation or a paddle/pushbutton for single shot measurement. Pulse parameters (duration, sample delay time and duty cycle) are controlled by an single chip microcontroller.

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Description

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The (sample & hold) pulse controller has 2 input sources: Footswitch and paddle/button.  During the time footswitch is engaged the controller is active in a repetitive mode. Single shot operation when button is pressed or keyer is momentary tapped. 

When active (short) CW pulses are send to the transceiver.  Via the RF power coupler and (diode) detector a proportional (pulsed) DC voltage is generated, this signal is fed back to the puls controller. The pulse controller will measure the (peak) voltage of this signal, holds it for long time and fed the output to a DC voltmeter. Measurement of the peak voltage will be done after some specific delay, to accomodate CW settling time of the used transceiver.

Detailed operation description

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Transceiver CW IN will be asserted for approx. 20 ms, when FOOT input is activated. Transceiver will output full (set) power after some time due to CW shaping parameters specific to the transceiver used.  Via an externale coupler some voltage will be developped proportional to the RF output power. This voltage will be sampled after some specifc time (20ms) via a Sample and Hold circuitry. Output of this sample and hold is output and can be measured via a DC voltmeter.

"Gain" between sampled RF out voltage and DC output is one.

The dutycyle of the RF output will be 3:4 (on:off) resulting in less than half average power dissipation in poweramplifier and dummyload.

 



Schematic

For a .pdf version of the schematic select the diagram below or click here 

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Upon the SINGLE input is grounded a single measurement is started. First the CW-OUT output is grounded, after 20 ms a sample of the ANA_IN input is taken by the sample&hold AD582, this to ensure that full power is achieved. CW-OUT output is released and due to the sample&hold functionality the peak value of the input value is constantly output and can be measured with a DC voltmeter. In case FOOTSWITCH input is grounded this proces is repeated every 140ms. With this timing still smooth tuning can be achieved and observed. The exact timing is controlled by an ATMEL AVR ATiny13 microcontroller. 


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Software

Software is developed in C using AVR Studio 5 and WinAVR GCC C compiler for AVR ATtiny13 and can be downloaded here. Internal 9.6 MHz oscillator is used and fuse setting are the factory default ones.

 

Copyright © 2011 Carel Mobach, PC5M

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