On Tue, 18 Jan 2005 21:29:16 GMT, Bruce in Alaska
wrote:

In article .com,
wrote:

More theoretical than anything ...

A cold night's discussion evolved into: if my radar is picking up a
target (a buoy in the case of this discussion) at whatever range in a
dead fog, I'll lose it when it gets close enough to where I can
physically see it (50 yards was the distance mentioned, but you can't
see anything at 50 yds in a dead fog .. but you get the idea).

If that's the case; i.e., losing a radar target when you close on it;
is it merely the way radar works, or is the radome mounted incorrectly
or are there other variables I'm unaware of insofar as radar and
minimum range/tuning?

Thanks

Gary


There are a number of things that make up MRR (Minimum Radar Range)

1. The PRR (Pulse Repition Rate) and PL (Pulse Length) of the
Transmitter, and the RGD (Receiver Gate Delay) of the
Receiver all effect the "Minimum Radar Range". The first
two you have no control over, but the RGD is usually set
when the radar is installed, for the vessels installation.
2. The VB (Vertical Beamwidth) of most Radar Antennas is in
the neighborhood of 25 Degrees. 12.5 above and 12.5 below
the Horizontal center of the antenna. If the antenna is
mounted up HIGH, (Like over 30 meters) like a Large ship
then the 12.5 degree lower Beamwidth will lose the target
much sooner that one mounted at sat 3 meters. So antenna
hight, and antenna VB, need to be taken into consideration
during installation.
3. Antenna Shading can also play a significant roll in MRR.
When a Radar antenna is place at the rear of a vessel,
and must look forward thru all the masts and rigging of
Say, a sailboat, then all that stuff deflects and obscures
the RF Pulse that the radar produces and the return echo
that it needs to show the target. The narrower the HB
(Horozontal Beamwidth) of the antenna, the better it will
decern targets, near or far. This is why Radar Antennas
should be mounted where they have a CLEAR, unobstructed
view, forward.


Hope that helps......


Bruce in alaska


Nice post, Bruce!

Brian W