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2 Meter Tape Measure Antenna Questions

Sep 27th, 18:56

K3OHU

Joined: Apr 4th 1998, 00:00
Total 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, 09:55

W1VT

Super Moderator

Joined: Apr 4th 1998, 00:00
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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