Marc,
Excellent advice, but I would also like to add that power is your freind and
it is not just for distance, as the radar mount will always be low in
height, but it is for small partially submerged objects that are close that
when struck could ruin your day. (like containers) Another important fact
about 6' radiators is that the vertical fan is close to 20 degrees, as
opposed to a 4' radiator's 30 degree fan. If, as in my case, mounting the
antenna on an aft bridge, it means that a 6' radiator will not radiate the
center cockpit and a 4' will. Marc has advised anyone to witness the radar
you intend to buy before you buy it is imperitive. I helped install two
Kelvin Hughes commercial radars on a super yacht last summer. Both of these
drove 17" marine LCD screens at a very high resolution. They had 4'
radiators. The ability of these radars to discriminate targets at close
range was appalling. I am not a radar expert, but I do know that everybody
that is anybody buys Furuno for a reason. It is not unusual to see 20,000
hours of transmit time without failure. That says a lot.
Steve

"Marc Heusser" d wrote in
message ...
In article ,
"Glenn Ashmore" wrote:

Anyone know anything about Koden radars? Koden owns Sitex and is known
for
making high end commercial radars but they have a new (to me) line of
recreational units at in a very good price range. Low end is a 7" color
display with a 2KW radome for a street price around a boat buck. The 10"
2
KW is just under 2 boat bucks. Both have C-mapNT chart plotter
capability
with split screen. You can link up to 3 displays through a standard
Ethernet hub and the 7" display is just $600. Not wild for the squared
off
blue case but for 40% less than anything else with the same features it
looks like a pretty good deal.

Simrad's antenna-scanners are made by Koden actually - and they have a
very good name over here.

Koden has a very long standing in the RF community (amateur radio etc).
Depending on where you use it, 10" is the minimum display size. On
rivers over here for commercial vessels you are required to have at
least a 6' open array antenna (that defines resolution).

The formula for the horizontal width of a radar beam is
radio beam width [degrees] = 70 * Wavelength [m] / Antenna Length [m]
for the X-Band (9.4 GHz) the wave length is about 0.03m, so the formula
simplifies to
radio beam width [degrees] = 2.1 / Antenna Length [m]
ie a 40 cm radome gives 5.6°
a 65 cm cm (2') radome gives 3.2°
a 90 cm (3') open array gives 2.3°
a 120 cm (4') open array gives 1.8°
a 180 cm (6')open array gives 1.2°
The requirement on the river Rhine is to separate two objects 10 m (33')
apart from a distance of 400 m (0.2 sm), therefore the minimum 6' open
array antenna.

The faster the boat (less advance warning) and the busier and narrower
the waters the more resolution you need.

On open waters resolution may be less of a concern.

So while other requirements are nice, I'd go for at least a 4' open
array antenna as the three top items on my requirements list, and at
least a 10" monochrome display (if you cannot avoid it 7" but one tends
to get older :-). All the other requirements come after that.

I would have no reservations whatsoever to get a radar from Koden. Their
scanners rank among the best.

As for the operating unit you'd have to check features - map overlay is
very nice to have (especially when you are less acquainted with the
waters), good filters too (there are excellent digital filters - but
probably only available on commercial units), autoranging tuning, gain
etc are nice (but not all of them work well!), trails or miniARPA/MARPA
are nice too (but will be supplemented/supplanted by AIS, already in
operation for commercial vessels in Europe).

If you can, test the radars beforehand - and be sure to see the
difference between antenna lengths - eg a 1.5' radome to a 4' beam in
tight waters and no sight, ie navigation by radar alone.

I learnt very much aboard a professional vessel on a busy narrow river
with bridges, nearby building etc and blocked sight. Be sure to train
reading the radar under actual conditions.

HTH

Marc

PS: After a quick look on their website I'd personally go for the
MDS-1040-4 (possibly -3) as a budget choice, if very tight for a MDC-740
with 4' antenna

--
remove bye and from mercial to get valid e-mail
http://www.heusser.com