[amsat-bb] Re: Antenna element and Boom material

i8cvs domenico.i8cvs at tin.it
Wed Aug 14 18:24:11 PDT 2013

Hi Mike, N6IMF
     Russ, K0WFS
     and All on the list

Generally speaking, if the elements of a yagi antenna are mechanically
mounted insulated over a metallic boom like a round or square aluminum
boom than the effect of the boom is to SHORT the lenght of the elements.

The same shortening effect affect the element lenght if the elements are
mounted directly in contact over or inside the metallic boom.

No matter if the boom is round or square the lenght of the elements
will be shortened in comparison to mount the elements over a plastic
insulated  boom.

The plastic material as used for the boom do not affect the elements lenght.

BTW in your case if you mount the elements over the boom in the same
manner as designed for 1/4 inch round elements than to change the size
elements from round 1/4 inch to about 3/8 inch square will affect only
a small amount the center resonance of the antenna at the working center
frequency and hence his change in VSWR and performance will be
very small.

Please read the following references on this matter:

1)P. Viezbicke, "Yagi Antenna Designe" NBS Technical Note 688,
    1976, page. 6

2) Guenter Hoch, DL6WU, "Extremely Long Yagi Antennas ,VHF
     Communications 3/82, pag.130

3) J.E. Pearson ,KF4JU, Element Lenght Disturbancies Due to End
     Chamfering and Insulated Metal Boom" Proceedings of the 22nd
     Conference of the Central States VHF Society.

4) J. Lawson,"Yagi Antenna Designe" ARRL 1° Edition 1986 ,
     pages. 7-11

5) The ARRL UHF/Microwave Experimenter's Manual,ARRL
     1990 pages. 9-5

6) R. Bertelsmeier, DJ9BV, "Yagi Antennas for 144 MHz DUBUS
     1/1990 pag. 23

Have fun

73" de

i8CVS Domenico

----- Original Message -----
From: "Russ Ramirez" <russ.ramirez at gmail.com>
To: <amsat-bb at amsat.org>
Sent: Wednesday, August 14, 2013 6:46 PM
Subject: [amsat-bb] Re: Antenna element and Boom material

> >I am wondering about going from 1/4 inch tound elements to about 3/8 inch
> square
> >would effect the performance of this antenna.
> >Mike Hoblinski
> >N6IMF
> It definitely will Mike, but not in a positive/negative way per se. Let me
> explain.
> If you follow an optimized design that called for 1/4 inch round elements
> and substitute 3/8 in square tubing, the impedance and SWR bandwidth
> characteristics will change in the general sense, and these changes may or
> may not be desirable. I do not have the experience with LP antenna
> implementations that I do with Yagi or wire antennas, so perhaps there are
> other issues to consider. I would suspect that the low SWR points across
> the bands would simply shift. Changes in element diameters generally
> affects the electrical length, and in your example only a small amount.
> Russ
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