Introduction

Radiofrequency Interference (RFI) is a big problem in Radio Astronomy. Often it is the case that the RFI is much stronger than the signal the astronomers try to detect. Thus it is extremely important that RFI is limited and its effects are minimized during an observation. RFI has been controlled to an extent through the Federal Communications Commission (FCC) and the International Telecommunication Union (ITU)--for example, the National Radio Quiet Zone (NRQZ) around the Green Bank Telescope (GBT) in West Virginia. Even then, Radio Astronomers have to deal with RFI since RFI from transmitters outside the RQZs are sometimes much stronger than the signal they are observing.

The GBT lies in the NRQZ, which was established by the FCC and the Interdepartment Radio Advisory Committee (IRAC) in 1958 ([Brundage(1981),Sizemore(1994)]). One source of RFI at the GBT is an ARSR-3 Air Surveillance radar. The radar is located 104 km southeast of the GBT at an azimuth of 163.87$\mbox{$^\circ$}$, at a latitude of  37$\mbox{$^\circ$}$31$\mbox{$^\prime$}$2$\mbox{$.\!\!^{\prime\prime}$}$ 0N, and longitude of  79$\mbox{$^\circ$}$30$\mbox{$^\prime$}$38$\mbox{$.\!\!^{\prime\prime}$}$ 0W. This is just inside of the NRQZ which encompasses latitudes 37$\mbox{$^\circ$}$30$\mbox{$^\prime$}$0$\mbox{$.\!\!^{\prime\prime}$}$9 to 39$\mbox{$^\circ$}$15$\mbox{$^\prime$}$0$\mbox{$.\!\!^{\prime\prime}$}$8, and longitudes  -78$\mbox{$^\circ$}$29$\mbox{$^\prime$}$58$\mbox{$.\!\!^{\prime\prime}$}$ 0 to -80$\mbox{$^\circ$}$29$\mbox{$^\prime$}$58$\mbox{$.\!\!^{\prime\prime}$}$5. The radar transmission frequency is approximately 1292.01 MHz.

Below we present a simple time-blanking procedure to remove the RFI from the radar to extract HI line-profile for the galaxy UGC4288. We first describe the data acquisition system setup, then the various radar parameters as extracted from the data. Finally we describe the method used to remove the radar from the data to extract the line profile for the galaxy.