Hi I want to display the frequency of a sweep signal in LCD i found some library but i don't know if i can use them or not because the frequency of signal is between 10 mhz to 20 mhz this is the library i found : freqMesure and freqcount
You could measure those frequencies with a stopwatch. You don't need an Arduino. Or did you mean "MHz"?
AFAIK, arduino with 16MHz clock could read digital port at 8 MHz max, to get 20 M upper limit use divider by 4, 2 D-trigger for example, as pre-selector
How quickly is this frequency sweeping? Do you need instantaneous readout of the frequency? The arduino probably can't do that. You need to count multiple pulses over a certain period. (The longer the period, the more accurate the frequency reading.)