Stationarity of wideband HF noise after interference excision

An essential element of HF communications systems is the excision of narrowband interference. The interference in the received signal is excised by first performing a discrete Fourier transform (DFT), then identifying and removing narrowband interferers in the frequency domain, and finally transforming the remaining signal back into the time domain via inverse DFT. In the present work the statistical F-test for variance equality was used to determine the stationarity of wideband HF noise and interference after excision. The most obvious result of this test is the systematic failure of the F-test near the DFT boundaries. This failure is due to short but large amplitude glitches present in the signal after excision, and occur at the beginning and end of the DFT interval. It is shown that the glitches are an artifact of the excision operation and are related to Gibb´s phenomenon. It is concluded that system designs will have to take account of this observation