"Nigel M" wrote in message
...
In rec.radio.amateur.antenna, Dave Platt wrote:

In this particular case, because the feed has an omnidirectional
pattern, it seems to me that there would be a definite advantage to
using a relatively "deep" and thus somewhat "pointy" parabolic
section, in which the focal point lies a fair distance back from the
forward-most edges of the actual reflector.

This is what I thought, but then I thought that this may make the
positioning of the focus much more critical.

My reason for posting was really to see if anyone had seen any research
on the optimum "depth" in this application.

I've been thinking some more about parabolas in general. It dawned on me
that the difference in shape isn't a change in formula as such, just the
range of co-ordinates that you use.

I reckon I can use Excel to draw one, but I'm not sure about finding the
focus, other than by measurement.

The practical field method.
You can find the focus my placing small mirrors at dishes edge and aiming
toward a light source.

gb