On Sat, 03 Apr 2004 18:40:53 GMT, Bruce in Alaska
wrote:

In article ,
bruce wrote:

Hi
I've got a JRC 1000 MKII, while shopping around i stumbled across an
aluminium cradle for the scanner/radome which would place the back of
unit
about 50mm forward of the mast. Is this too close to the mast? Granted
its
not likely that a collision would occur from directly behind without
setting off the guard alarm beforehand, would the proximity of the mast
cause any ghosting? Anyone else using a similar unit mounted on the
mast?

Is 20ft generally acknowledged as the optimum height above the deck?

It seems odd that the jrc instruction manual doesnt cover the placement
of
the dome in more detail.


cheers
bruce



The one thing that you will likely see, is a Shaded Zone where the
mast is. This is where the radar beam is blocked, and or redirected by
the mast. If the antenna is significantly wider than the mast, the
amount of blockage, and or redirection, is lower and as noticable.


Well, i thought the width of the beam was such that narrow objects allow
you t see 'thru', in a virtual sense, things like masts and poles? with
all the boats that have the radome on the mast they can se directly behnd
them. the actual mast won't be seen becaue the transmitt delay prevents
any returns shorter than 100' or so from registering on the screen (called
main bang supression)


Since as you say, being hit from the aft, is not a big problem,
this is just a bit of a nusense. The height above the deck,
is not really significant, except in the determination of the Maximum
range of the unit and the amount of healing that can be tolerated by the
radar.



in fact. this is the option that you choose best suited to your purpose.
If you want max range you mount as high as possible, if you want max
sensativity for close in work like harbour bouys and 'ejectae' mount low
and angle down a few degrees even.


Just make sure that if the antenna is an open slotline type,
that it won't hit you in the head while turning. (ouch) Most modern
radars have a 25 degree vertical beamwidth. This allows for healing in
most all Powerboat installations. Sail installations may require some
antihealing considerations.

not to be argumentative but the actual beam verticle width seems to be
less than that. experiment by mount on a pole on the aft quarter. most
boats are mounting this way now for practicle considerations.

rick

Bruce in alaska



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