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tokens: of for the central beam ( top ) and an offset beam ( bottom ) with a coma lobe at a position angle of . For the correction algorithm, we averaged the previously modeled side-lobe intensities on a fixed grid containing 2160 cells in cylindrical coordinates for the inner of the antenna diagrams. The cells have an azimuthal extent of and a radial extent of , covering the radial range of (first minimum) up to . 3.5.4. The far side lobes The far side lobes are determined by details of the telescope structure. It is difficult to measure these side lobes (e.g., Higgs 1967 ; Hartsuijker et al. 1972 ), so we used ray-tracing to model them. While in the near side-lobe range, details of each of the individual antenna diagrams need to be considered, and it is sufficient to use a single common far side-lobe diagram for all of the receivers. For the subsequent discussion of far-side-lobe effects, we consider the telescope as a transmitting system. The most important side lobes that are far away from the main beam of the 100-m telescope, were determined by Kalberla et al. (1980a, see their Fig. 3) . These are the stray cones, caused by reflection of plane waves from the primary mirror at the feed support legs. The second most important structure is the spill-over at the edge of the main reflector. Its irradiation level depends on the edge taper of the primary feeds. In addition, we considered spherical waves originating in the feeds and determined their reflections at the support legs. Figure 6 shows these structures. The eightfold symmetry is caused by the four legs. Each leg consists of four main tubes; two of them, separated by 1.98 m, are visible from the feed. These side lobes have an interesting structure, but it turned out that they are rather unimportant. Fig. 6 Side lobes caused by reflections of spherical waves from the feed at the support legs of the 100-m (intensities relative to main beam). The Effelsberg 100-m telescope has a Gregorian secondary focus with several feed systems in an apex cabin. The seven-feed system is situated in primary focus, and the roof of the apex cabin is closed during EBHIS observations. This roof causes reflections that are offset from the main axis by . The side lobes are easily determined from the geometry of the apex roof. However, that these reflections are oriented in the east-west direction makes the situation very uncomfortable since it can produce multiple reflections. A part of the rays being reflected off the apex roof can hit feed support legs located east or west of the roof. This causes secondary stray cones. Only a fraction of these secondary stray cones are reflected onto the sky. The other part is reflected to the main mirror, causing caustics. A minor fraction of the secondary stray cones can hit the fence at the rim of the reflector before escaping. These features were determined by ray-tracing. Figure 7 shows the resulting pattern. We disregarded further reflections caused by support legs to the