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

[Joe]

two other things to remember also.

1- the antenna will probably cost more because everywhere i know of 
square tubing is more costly than roung, but if you have a sourse OK,

2-  the wind load will be much larger, 30% roughly larger, the wind load 
of a 1 inch round tube is 0.6 the amount of a flat surface IE: square

Joe WB9SBD
Sig
The Original Rolling Ball Clock
Idle Tyme
Idle-Tyme.com
http://www.idle-tyme.com
On 8/14/2013 8:24 PM, i8cvs wrote:
> 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
>> K0WFS
>> _______________________________________________
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