On Mon, 21 Jan 2008 08:49:02 +0100, Marc Heusser
d wrote in
:

In article .com,
Peter Bennett wrote:

It is independent of your own radar - but must be mounted so that it
will not be triggered by your radar.

That is most likely impossible. At a few kW of transmitting power
(peak), it will trigger when the distance is only a few metres at most.

Marine radars have a limited vertical beam width, and the transponder
should be mounted above or below that vertical pattern. See the
Handbook:

If Sea-me is being fitted elsewhere, say on a radar arch, ensure that
it is above the superstructure of the vessel and that it is not
within the vertical beamwidth of any radar which may also be fitted.
Normally this means that the Sea-me antenna unit must be above or
below a 30° line from the centre of a radar antenna but you will need
to refer to your radar manual to confirm this.
....
Radars have many leakage paths and so Sea-me will respond to your own
radar’s pulses (typically a pulse is 1 microsecond long and is
repeated every 1 millisecond). The LED flash has been extended to 100
milliseconds to make it visible to the human eye and so it will be
permanently on when your own radar is transmitting. However Sea-me
transmits in response to an incoming pulse and so it will respond to
any which arrive in the spaces between the pulses put out by your own
radar. Typically the ratio of space to pulse is 1000:1 and so there
are 999 microsecond spaces for every 1 microsecond pulse received,
plenty of time for others to get in, even when electronic recovery
time has been allowed for. This effect does however mean that Sea-me,
because the active light is on, will be unable to tell you that you
are being struck by another radar. If this is a concern then you are
advised to switch your radar into its standby mode when you are not
actually using it. You probably do this anyway in order to save
power.

--
Best regards,
John Navas http:/navasgroup.com