As more amateurs are building Hydrogen Line radio telescopes, we are beginning to experience interference from strong adjacent out-of-band signals. The most common of these interference sources are Global Positioning System (GPS), Weather Facsimile (WEFAX), and Personal Communications System (PCS) satellites operating in the 1.5 to 1.7 GHz region; cellular telephone equipment operating in the 850 MHz segment; ISM equipment at 915 MHz; and DME/TACAN, air trafic control radar, and airborne transponder signals operating in the 960 to 1215 MHz band. Thus the 1420 MHz hydrogen line is surrounded by interference.