On Fri, 05 Sep 2003 03:16:26 GMT, "Ed Kelly"
wrote:

How high is that antenna mounted? It would have to be 70' up to have a
horizon at 12 miles. If it was mounted that high you would only be able to
see ships higher than 70' at 24 miles. Those would have to be some pretty
big ships for you to see them at ranges of well over 24 miles, no matter how
powerful the radar.

Ed

Antenna's up about 45'. Radio horizon is further than your visual
horizon and can be extended by temperature inversions. The other
thing to consider is the height of the target. A radar reflector a
hundred feet above the water or a large ship can be seen way further
than the horizon because he sticks up OVER it for quite a distance.



Larry

Extremely intelligent life must exist in the universe.
You can tell because they never tried to contact us.

"Larry W4CSC" wrote in message
...
On Fri, 05 Sep 2003 03:16:26 GMT, "Ed Kelly"
wrote:

How high is that antenna mounted? It would have to be 70' up to have a
horizon at 12 miles. If it was mounted that high you would only be able
to
see ships higher than 70' at 24 miles. Those would have to be some pretty
big ships for you to see them at ranges of well over 24 miles, no matter
how
powerful the radar.

Ed

Antenna's up about 45'. Radio horizon is further than your visual
horizon and can be extended by temperature inversions. The other
thing to consider is the height of the target. A radar reflector a
hundred feet above the water or a large ship can be seen way further
than the horizon because he sticks up OVER it for quite a distance.



I was using a radio horizon calculator to get those numbers. 45' gives you a
9 mile horizon. That means that (ignoring anomalies caused by atmospheric
conditions) that to see a target at 24 miles it needs to be 120' tall. I'm
not arguing that you can't see 24 miles with that 2KW radar - in fact a 12
KW radar would not be able to see any further than your radar given the same
conditions. Many people seem to think a higher power radar will allow them
to "see" further, while they are really constrained by geometry rather than
power. What the higher power will do is give you better discrimination (they
will see targets that you cannot)..

Ed

On Sat, 06 Sep 2003 02:49:20 GMT, "Ed Kelly"
wrote:


I was using a radio horizon calculator to get those numbers. 45' gives you a
9 mile horizon. That means that (ignoring anomalies caused by atmospheric
conditions) that to see a target at 24 miles it needs to be 120' tall. I'm
not arguing that you can't see 24 miles with that 2KW radar - in fact a 12
KW radar would not be able to see any further than your radar given the same
conditions. Many people seem to think a higher power radar will allow them
to "see" further, while they are really constrained by geometry rather than
power. What the higher power will do is give you better discrimination (they
will see targets that you cannot)..

Ed

Actually, what's MOST important is how CLOSE the radar can "see", in
the fog or in the dark. On the old boat, the 2KW Raymarine dome was
mounted about 15' off the water on a stern pole mount. On the 1/8th
mile range, I could see the masts of boats about 6 slips away, at the
edge of the transmitter's main bang. I think that's very nice when
you're feeling for that bouy in a fog bank or trying to avoid the
idiots fishing in the dark with no lights on.....

Moving it up to 45' has cost us about 4 slips because the bottom of
the radome is supposed to protect us from the radiation, probably
something some government bureaucrat dreamed up to make himself a job.
From a 2KW peak power radar with a piece of printed circuit board for
an antenna? How stupid. Well, nothing I can do about it. The deck
on the Amel Sharpi is covered with sails from the bow way past the
stern....(c;


Larry

Extremely intelligent life must exist in the universe.
You can tell because they never tried to contact us.