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How to measure the distance between elements?

Jun 7th, 13:23

KO2F

Joined: Jun 17th 2011, 23:48
Total Topics: 0
Total Posts: 0
When constructing an antenna with elements of any significant size, where is the distance between elements measured? For example...

If I am constructing a Yagi with 1 inch tubing and the design calls for 16 inches between 2 elements, does this mean:

a) 16 inches between the outer element surfaces? Meaning that the two elements are 17 inches apart on center...

b) 16 inches on center?

x...) something else?

If I am constructing a 10 foot diameter double loop for 160 meters, this 1 inch question could mean a difference of more than 6 inches in length.

Bob
KO2F
Jun 7th, 13:32

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
All the computer modeling programs that I have seen use the center to center distance. Very few people have a test range for optimizing 2M antennas via trial and error.

This article attempts to explain Yagi dimensions
http://www.arrl.org/vhf-beams
Homebrewing a 6-Meter Yagi (from QEX RF column)
QEX January/February 1998, p. 52-57
Enlarged Figure 6 with key dimensions. Zipped file with all figures and photos.

In the past I've measured distances off a photo to see which option seemed most reasonable. These days imported dial calipers are inexpensive measuring tools.

Zak W1VT
ARRL Senior Lab Engineer

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