This thesis provides a description of transmission and reception of a narrow- hand signal using a soundcard for pilot tone detection in spectrum sensing. The energy of pilot tone and the signal around bandwidth of 25 kHz are calculated and the energy of the spectrum is compared with test statistics. The method is based on noise and signal plus noise statistics. The energy detection of a random signal with white Gaussian noise is reduced to the sum of squares of statistically independent Gaussian random samples. When the signal is absent, the statistics of the energy is chi-square distributed. If the signal is present, statistics has non-central chi-square distribution with a non-centrality parameter which is a function of the signal strength. The probability density function (pdf) of energy of noise and signal plus noise is analytically calculated. A phase locked loop(PLL) is used to synchronize the local oscillator with the carrier of the received signal. Designed and implemented highpass and lowpass filter using bilinear transform as a component to use in the PLL. Probability of error and probability of false alarm for the signal plus noise are calculated. Obtained the optimum value of threshold the decreasing amplitude for different observation time.