How to clamp an input signal to propeller?
I have developed an automatic antenna tuner for amateur radio applications. I sample the frequency of the signal being transmitted through one of the prop pins, to preset my tuner components to the proper settings via stepper motors. At 10 watts signal strength, my frequency sample is about .8v pep, and at 100w the sample is about 1.88v pep. But, when I apply full legal power of 1500w, the freq sample goes to above 5v. I have tried resistive pads, but to reduce the 5v to 3.3v they reduce the lower power readings to something below what the propeller can read. I have also tried a zener diode to clamp the voltage, but it seems to reduce the voltage as well at the lower power readings, below the clamping voltage desired. Does anyone know how I can buffer the input to the propeller? All I need from the measurement is the frequency, but I am concerned that at the higher power, I may damage the prop. I need to limit the voltage of the frequency measurement at the higher power settings, but not the signals below 100w. Any suggestions for a buffer that can accomplish this? The frequencies I am measuring are between 3.5 - 28.5 Mhz.