2 Meter Tape Measure Antenna Questions
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| Sep 27th 2022, 18:56 | |
K3OHUTotal Topics: 0 Total Posts: 0 |
1. Why are the element lengths on the 2 meter tape measure antenna so much shorter than the calculated lengths for the 2 meter band. eg. Each half of the driven element is 17 3/4 inches. Calculations result in a length of 20.2 inches for 146 mhz. 2. Why is the reflector so much closer to the driven element than the director. It's usually the other way around. |
| Sep 30th 2022, 09:55 | |
W1VTSuper Moderator Total Topics: 0 Total Posts: 0 |
The effective diameter of the tape measure is much greater than a thin wire or rod. As the diameter increases the resonant frequency increases and the elements need to be shorter. http://theleggios.net/wb2hol/projects/rdf/tape_bm.htm https://www.instructables.com/The-Tape-Measure-Antenna/ This design uses a hairpin match. The driven element is cut shorter and an inductor is placed across it to effectively step up the feedpoint impedance. The gain of a Yagi is a function of boom length, not the number of elements. With just 3 elements more gain can be obtained by making the driven element farther away. Zak Lau ARRL Senior Lab Engineer |
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