Thread: Ketch Radar
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Larry Larry is offline
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First recorded activity by BoatBanter: Jul 2006
Posts: 5,275
Default Ketch Radar

Gordon wrote in news:13dti6knj5hh173
@corp.supernews.com:

If I mount the radar on the mizzen mast, how much signal will be
blanked by the main mast on a 36 footer?
G


None. The antenna in the little radome is a WIDE piece of printed
circuit board with a phased antenna array cut into it at 10Ghz. As it
sweeps across the main mast and rigging, a return shadow of RF from the
target sweeps across the face of this WIDE phased array, but only cuts
off the return signal to a few elements, never the whole antenna, so you
never miss anything because of the shadow. It sees targets just fine way
further away than you need racing along at 6 knots.

Imagine you are standing at the bow exactly opposite of someone on the
opposite side of the mainmast. Because he is narrow, you can only see
the edges of him on either side of the mast. But, to see what the effect
of the WIDE antenna is, have him hold a linear tube flourescent light
sideways in front of him. The flourescent light tube sticks out both
sides of the mast. The further away from the mast he is, the more of the
light's tube you can see from your side. Look at the boat behind you.
Do you see the shadow of the mast from the light? No, because MOST of
the light's tube is always exposed on either side of the mast. There is
no defined shadow, only a slightly-less-lighted area that's quite wide.
The effect on the radar illuminating the target is very similar from its
wide antenna. It isn't as sensitive as it is to the side pointed through
the mast....but the mast doesn't make a big hole in its coverage, which
is the point. You'll see that big bouy before running it down....(c;

Larry
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