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
Guenter Hoch, DL6WU, "Extremely Long Yagi Antennas ,VHF Communications 3/82, pag.130
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.
J. Lawson,"Yagi Antenna Designe" ARRL 1° Edition 1986 , pages. 7-11
The ARRL UHF/Microwave Experimenter's Manual,ARRL 1990 pages. 9-5
R. Bertelsmeier, DJ9BV, "Yagi Antennas for 144 MHz DUBUS 1/1990 pag. 23
Have fun
73" de
i8CVS Domenico
----- Original Message ----- From: "Russ Ramirez" [email protected] To: [email protected] 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 _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb