Bias voltage decrease

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radium98
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Bias voltage decrease

Post by radium98 » Sat Oct 07, 2017 4:30 pm

Hi can any expert explain me how i can decrease the bias gate from the swr reflected voltage that is going from a directionel coupler to lower down the rf output when i have swr do i need any transistor or circuit in between ??
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Analyser
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Re: Bias voltage decrease

Post by Analyser » Sat Oct 07, 2017 5:41 pm

Yes, you can use the reflected signal from a directional coupler to switch on a transistor or send signal to an op-amp which will disable the bias. You need to be careful to incorporate a latch circuit because when the power is reduced the reflected power will also reduce, this can result in an oscillation between full power and low power.

radium98
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Re: Bias voltage decrease

Post by radium98 » Sat Oct 07, 2017 5:56 pm

Guru man Analyser thanks a lot the transistor must be pnp in this case or npn i dont totaly need to cut off the bias only reduce it is volt from 5v to - to reduce the power this is my condition only i am taking the result and i will experiment later
thanks another time freind analyser

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Re: Bias voltage decrease

Post by Analyser » Sat Oct 07, 2017 7:49 pm

Voltage coming from directional coupler will be positive so you can use an NPN transistor. Feed voltage from the coupler in to a preset, then to base of the transistor. Collector an emitter can go across supply line of RF transistor bias pot or bias supply.

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Re: Bias voltage decrease

Post by radium98 » Sun Oct 08, 2017 7:04 am

Analyser thanks man great.thanks

radium98
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Re: Bias voltage decrease

Post by radium98 » Mon Oct 09, 2017 7:28 pm

i did not clearly understand the meaning by preset ? is it a potentiometer to limit ceratin value ?
or a comparator with a threshold limit ?

Albert H
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Re: Bias voltage decrease

Post by Albert H » Mon Oct 09, 2017 8:45 pm

By "preset" he means a screw-adjusted variable resistor or potentiometer. It's commonly called a "preset" because it was adjusted once during manufacture (so it was "pre-set" at the time of manufacture) usually to adjust for tolerances in other components.
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Re: Bias voltage decrease

Post by radium98 » Tue Oct 10, 2017 10:27 am

thanks Albert H

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