Bias voltage decrease

[radium98]

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 ??
Regards

[Analyser]

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]

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

[Analyser]

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.

[radium98]

Analyser thanks man great.thanks

[radium98]

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]

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.

[radium98]

thanks Albert H