[MLB-WIRELESS] Focal length of 24dBi conifer antenna
wireless at smithsgully.net
Mon Jul 21 21:04:54 EST 2008
If you make a couple of simple measurements, ie width and depth, you can
calculate the focal length.
As per this page:
However that isn't the whole story, you need to know where the "Phase
Centre" of the feed is. The phase centre of an antenna is the point at
which the wave front appears to radiate from spherically. It is the
phase centre of the feed that needs to sit at the focus. Depending on
the type of feed, the phase centre could be somewhere along the axis of
the feed or even behind it in space. Unfortunately the position of the
phase centre isn't easily predicted or measured.
For a given type of dish and feed, it may be better to get someone to
measure the distance from the bottom of the dish to the back of a
reflector or the front in the case of a cantenna type feed.
Michael Borthwick wrote:
> Can someone please advise the focal length of the 24dBi conifer antennas
> Melbwireless mailing list
> Melbwireless at wireless.org.au
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