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"Crazy George" wrote:
Well, let me just post this at the bottom. RCA made a line of VHF TV transmitting antennas which were a slot arrays. The only one I managed to get close to before it became airborne and clamped a thousand or more feet in the air was for channel 9. It was 80 feet long (2 - forty foot sections) and was constructed exactly as Tom, K7ITM suggested, the phase of the feed of each element was progressively changed, in this case, to effect 1.50 of downtilt. _______________ The antenna described above is the RCA "Traveling Wave" design. Without beam tilt for the situation described, it has an omni, horizontal plane RMS gain of ~17.2X (~12.4dBd) . The beam width within the 3dB points on its elevation pattern is about 3.2 °. If this antenna was placed with its radiation center 1,500 feet above smooth earth, the radio horizon would be 0.59° below the horizontal plane, so using beam tilt would raise field strength there. The 1.5° value stated above exceeds that, but there may have been good reasons for it. Adding beam tilt to an antenna with a very broad elevation pattern, and installed on a short tower is a waste of time and money, however. RF (RCA Broadcast Field Engineer, 1965-1980) Visit http://rfry.org for FM transmission system papers. |
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