Gridpacks and focal point with yagi/biquad

[VK1JA]

A quick question that I haven't been able to find an answer for via Google regarding gridpacks (probably relates to dishes as well) and using small yagis or biquad antenna for the feed....

When mounting the yagi or biquad, do you mount it so the focal point is at the driven element, the first director (when using a small yagi) or at the reflector?

I understand other factors may come into the thinking regarding over and under illuminating the gridpack/dish etc, and ideally you'd adjust the antenna for peak signal, but I'd would like to know where to start from !

73

Jayson

[VK4VU]

Hi Jayson,

Most of the answers can be found in the information published by Paul W1GHZ (ex N1BWT)

http://www.qsl.net/n1bwt/chap6-2.pdf

It looks like the phase center (centre ?) is around 0.25 - 0.27 wavelengths behind the active element of the feed.

Hope this helps.

Regards,

Rod VK4VU

[VK1JA]

Thanks Rod, lots of good info in that link, I'll have a read later.

73