Parabolic Reflector Template

[elder]

One consideration for a home made antenna is parabolic reflector elements rather than a flat plate. A convenient way to draw a parabola for a template is to use a square. First determine desired focal length then mark off two points to represent apex and focal point. The first lines drawn will be a 90 degree angle, then draw successive lines with the square laid from the focal point to the vertical element of the 90 degree angle. The lines from the focal point do not need to be drawn, I include several just for illustration. The inside of the conglomeration of lines drawn will represent a parabola. The paper can be folded and traced to get the bottom half rather than drawing all the lines.

The template can be traced onto a suitable support and drilled for insertion of elements of proper length for frequency range. For UHF use a bow tie feed.

 

[Tower Guy]

One consideration for a home made antenna is parabolic reflector elements rather than a flat plate. A convenient way to draw a parabola for a template is to use a square.

Another way is to bend a reflector pipe with a tight cable like a bow and arrow. The shape of the pipe will be a parabola.

 

[elder]

Another way is to bend a reflector pipe with a tight cable like a bow and arrow. The shape of the pipe will be a parabola.

I recall a ham radio article on that years ago. It sounds like a much easier way to do it. How do you find the focal point, is it as easy as being where the cable would cross the bore sight?

 

[Tower Guy]

I recall a ham radio article on that years ago. It sounds like a much easier way to do it. How do you find the focal point, is it as easy as being where the cable would cross the bore sight?

No, the focal point depends on the amount of bend.

The Ham Radio magazine article was written in the '70's by K2RIW. He made a 24' round stressed parabolic antenna.

I'd propose to build a plane parabolic that looks something like this: http://www.kathrein-scala.com/catalog/PR-950.pdf

The size could be as large as 12' x 8'. Such an antenna would have about 25 db gain.

 

[elder]

No, the focal point depends on the amount of bend.

The Ham Radio magazine article was written in the '70's by K2RIW. He made a 24' round stressed parabolic antenna.

I'd propose to build a plane parabolic that looks something like this: http://www.kathrein-scala.com/catalog/PR-950.pdf

The size could be as large as 12' x 8'. Such an antenna would have about 25 db gain.

Thanks, of course the focal point is not on the cable, I don't know what I was thinking (probably wasn't thinking)! There is an easy formula for measuring and calculating the focal point of a parabola, but one could probably mount the feed so it could be easily slid into the best focus for the desired channel.

I haven't tried the parabola, but once built a 21 element yagi with a corner reflector for channels 71-73 (translator channels) using a broom stick for the boom and coat hangar wire for the elements.

Again, thanks.