Abstract. Various methods of radio frequency interference (RF I) mitigation methods at radio astronomy telescopes are being considered. Special attention is given to real-time processing algorithms. Computer simulations and observational results are used to describe the applicability of these methods. Best results can be achieved when the RF I mitigation procedures are adapted to the particular radio telescope, the type of observations, and the peculiarities of the RF I environment. A combination of different linear and non-linear methods in the temporal and frequency domains, with and without the use of reference antennas, may give considerable suppression of strong RF I.

A selection of statistically stable (robust) algorithms for data variance calculating has been made. Their properties have been analyzed via computer simulation. These algorithms would be useful if adopted in radio astronomy observations in the presence of strong sporadic radio frequency interference (RFI). Several observational results have been presented here to demonstrate the effectiveness of these algorithms in RFI mitigation.

The sensitivity of radio astronomical stations is often limited by man-made radio frequency interference (RFI) due to a variety of terrestrial activities. An RFI mitigation subsystem (RFIMS) based on real-time digital signalprocessing is proposed here for the Westerbork Synthesis Radio Telescope based on a powerful field programmable gate array processor. In this system the radio astronomy signals polluted by RFI are ''cleaned'' with the RFIMS before routine back-end correlation processing takes place. The high temporal and frequency resolution of RFIMS allows the detection and excision of RFI better than do standard radio telescope back-end configurations.

The transmission rate of communication between radio telescopes on Earth and extraterrestrial intelligence (ETI) is here calculated up to distances of 1000 light years. Both phase-shift-keying (PSK) and frequency-shift keying (FSK) modulation schemes are considered. It is shown that M-ary FSK is advantageous in terms of energy. Narrow-band pulses scattered over the spectrum sharing a common drift rate can be the probable signals of ETI. Modern SETI spectrum analyzers are well suited to searching for these types of signals. Such signals can be detected using the Hough transform which is a dedicated tool for detecting patterns in an image. The time-frequency plane representing the power output of the spectrum analyzer during the search for ETI gives an image from which the Hough transform (HT) can detect signal patterns with frequency drift.