Coherent Sampling Calculator

This calculator computes the coherent sampling frequency and coherent input frequency for configuring coherent sampling in FFT analysis.

Without coherent sampling, FFT analysis suffers from spectral leakage. Coherent sampling follows these rules:

The signal under test must be divided into periods
F_s/N = F_t/M, where F_s is the sampling frequency, N is the number of samples, F_t is the signal frequency, and M is the number of sampled periods
M and N must be mutually prime integers, which avoids redundant sampling and improves efficiency

Input and output parameters

f_DSAMPLE	Sampling frequency
f_DIN	Enter frequency
N_RECORD	Number of FFT data points
SIGFIG	Signal generator resolution, decimal places after MHz
f_CSAMPLE	Result: coherent sampling frequency
f_CIN	Result: coherent input frequency

f_DSAMPLE(sampling frequency)

MHz

f_DIN(input frequency)

MHz

N_RECORD(FFT data points)

SIGFIG (signal generator resolution)Decimal places after MHz

Result:

f_CSAMPLE(coherent sampling frequency)

MHz

f_CIN(coherent input frequency)

MHz

Formula

Step 1: calculate the basic frequency resolution

H = f_DSAMPLE / N_RECORD

Step 2: round to the specified precision

K = round(H, SIGFIG)

Step 3: calculate the coherent sampling frequency

f_CSAMPLE = K × N_RECORD

Step 4: calculate the number of periods (nearest odd integer)

G = (f_DIN / f_CSAMPLE) × N_RECORD

J = odd(⌊G⌋ + 1)

Step 5: calculate the coherent input frequency

f_CIN = (f_CSAMPLE × J) / N_RECORD

Tip:Window functions can be an alternative to coherent sampling for reducing spectral leakage, but cannot eliminate it entirely. Common windows include Hann, Hamming, and Blackman — choose according to your needs.