Koden radars?

Thanks. I have the Furuno on my list to look at. Finaly I am almost to the
stage that I can invite my banker out for a tour and a discussion about
financing the spars and electronics. That's why I am back looking at what
has been happening in radars, autopilots and nav instrument systems for the
last 2 or 3 years.

On other points of progress UPS just delivered a pair of Harken 53 primaries
and a couple of 44s for the cabin top. With the electric 46 I scored on
ebay my winch compement is complete. Also the last of the Spinlock clutches
are ready to install and the vacuum insulation is installed in the
refrigerator box and I go to bed every night high on varnish fumes and
sanding dust. But the best part is that everything but the spars, sails,
electronics and top side paint is on hand, ready to be installed and PAID
FOR!.

One of these days I am going to have to find the time to update the web
site. There is just nothing other than the teak side decks to get inspired
to write about in about all the little details I have been working on for
the last 2 years but I'm getting threatning emails from Moscow wanting an
update.
 >> Stay informed about: Koden radars? 

On Tue, 1 Jan 2008 19:51:53 -0500, "Glenn Ashmore" <gashmore.DeleteThis@cox.net>
wrote:

>Thanks. I have the Furuno on my list to look at. Finaly I am almost to the
>stage that I can invite my banker out for a tour and a discussion about
>financing the spars and electronics. That's why I am back looking at what
>has been happening in radars, autopilots and nav instrument systems for the
>last 2 or 3 years.
>
>On other points of progress UPS just delivered a pair of Harken 53 primaries
>and a couple of 44s for the cabin top. With the electric 46 I scored on
>ebay my winch compement is complete. Also the last of the Spinlock clutches
>are ready to install and the vacuum insulation is installed in the
>refrigerator box and I go to bed every night high on varnish fumes and
>sanding dust. But the best part is that everything but the spars, sails,
>electronics and top side paint is on hand, ready to be installed and PAID
>FOR!.
>
>One of these days I am going to have to find the time to update the web
>site. There is just nothing other than the teak side decks to get inspired
>to write about in about all the little details I have been working on for
>the last 2 years but I'm getting threatning emails from Moscow wanting an
>update.
>

Good going, and thanks for the update.

Spars, sails and electronics can begin to add up as I'm sure you know.
I completely re-rigged a Cal-34 20 years ago and even with a lot of
sweat equity it still cost over $20K, probably double that by now.

We regard the autopilot as one of the most important pieces of
electronics on the boat, absolutely indispensible for long distance
cruising. Wish we had a backup for it.
 >> Stay informed about: Koden radars? 

In article <kbsej.24684$Ft5.530@newsfe15.lga>,
"Glenn Ashmore" <gashmore.TakeThisOut@cox.net> 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>
 >> Stay informed about: Koden radars? 

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" <marc.heusser.TakeThisOut@byeheusser.commercialspammers.invalid> wrote in
message news:marc.heusser-CEEB75.17012302012008@news.uzh.ch...
> In article <kbsej.24684$Ft5.530@newsfe15.lga>,
> "Glenn Ashmore" <gashmore.TakeThisOut@cox.net> 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>
 >> Stay informed about: Koden radars? 

In article <flji7g$rsi$00$1@news.t-online.com>,
"Steve Lusardi" <stevenospam RemoveThis @lusardi.de> wrote:

> 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)

Power is automatically reduced in all radars for closer ranges. And with
the typical 50 microsecond pulse at short range a range of 15 metres
around your antenna is blind anyway.

The key issue is learning to adjust and read the radar, again and again,
under good conditions blocking the radar operator's sight.

There is an excellent simulator to train by the way from
http://www.lightmaster.co.uk/Radar/LightMaster_Radar_Simulator_Mk2
I found it when training for the Long Range Certificate, they have a
simulator too for GMDSS DSC VHF, very useful to train distress calls.

If had to start again, I'd first get the simulator, then go through a
course, and only then select and buy the radar. I had the luck to get
good advice from a trainer.

From own experience in training for the radar certificate (Rhine at
Basel, 200 meters wide, commercial ships up to 135 m long crossing at 30
m lateral distance, bridges with support towers, narrow ports etc...),
objects vary wildly in reflection, eg you may easily mistake a goose on
the water or a duck flying by for a small rigid bottom inflatable power
boat WITH a radar reflector (-> emergency stop of a 30 metre fire boat
when cruising under radar only - real time simulation of dense fog
or the next navigation mark with radar reflector at times. On the lake
of Zurich we have ferries for cars - they have two parallel faces in
their superstructure - this makes for a great multiple echo, even of
your own boat ... the same can happen with oil storage tanks, regularly
planted trees, a motorway bridge ... All this on a river quietly
streaming. We were trained for failures too, be it rudder broken, radar
failing or motor. It does give you confidence when you know what to do.

I learnt too that you must not have a radar without VHF to call
approaching vessels - on a river to call around bends, or negotiate
crossing port to port or starboard to starboard crossing. AIS goes one
step further as it broadcasts your position, heading, speed, size of the
vessel, destination continously and includes the MMSI, so you can
selectively call approaching vessels. Simrad has a unit for recreational
boats.

A narrow river is much more demanding than open waters in this respect.

Knowing the waters (or at least having a good chart, preferrably
overlaid) is key. A flat coast will be much closer as it seems because
the reflections do not come from the waterline but from the next tree,
house, boulders, ...

> 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.

You can get that on a small boat if you have the same 4' antenna.
(They might have some digital filters that help some more, but you get
most of it.)
Actually on a super yacht I'd get a larger open array (IF I had the
money for the yacht...) - at least 6', preferrably more.

> 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

There are other choices, Furuno is not the only one. Swissradar has some
pretty nifty digital filters for example.
(Check eg
http://www.apple.com/downloads/dashboard/information/swissradar.html if
you have a Mac - 3 weather radars map the current rainfall for the whole
of Switzerland, 100 by 200 sm)
Koden (Sitex) might actually try hard and be successful at it.

On a small boat the combinations become important, as you might not have
the space for a separate echo, chart plotter, radar and AIS display.
A good balance of technical specs with space requirements and user
interface is what you are typically after.

My Simrad has a rather good auto setting on tuning/gain/etc, which for
me is a big advantage as I expect other people to operate it with even
less experience than myself. Along with the good chart overlay and a
very flat unit to mount this tipped the scale. It does not have a MARPA
on the other hand, but its trails work well as a substitute. The user
interface is clear but not as nice as Mac OS X or my TomTom GPS for the
street. (BTW their manual at
http://www.simrad-yachting.com/Products/Leisure/Navigation-Fishfinding/CX
44-NavStation/Downloads/
has a good explanation of radar operation and what sorts of displays can
be handy - off centre display is one of them, what is behind you is less
interesting than what's ahead).
And I knew Koden as an electronic engineer, so I did not have any doubts
there. Simrad's key expertise is actually echo sounders but their radars
have a good reputation for a reason too. In yachting they are well known
for their autopilots.

On my small boat I could install a 4' open array antenna, which still is
useful. I would not want anything less. Bear in mind also that larger
antennas often have a smaller vertical beam, which is NOT what you want
on a small boat, because it is rolling and you still want to see.

It might be worthwile to check some of the articles referenced in
http://marinedirectory.ybw.com/reprints/results1.jsp
a search for "radar chart" from 2005-2007 in Category Electronics turns
up this eg
Buying a radar plotter Practical Boat Owner Jul 2006 p76-79  (4.00
pages) etc
before testing and buying equipment.
The reprints are not free but most likely worth the money.

HTH

Marc

--
remove bye and from mercial to get valid e-mail
<http://www.heusser.com>
 >> Stay informed about: Koden radars? 

Sorry Marc, you are not correct, power is not reduced at lower range
selections. The transmitter tube is a magnetron, which effectively is a
resonant cavity within a permanent magnet. It is excited by driving the
cathode severely negative with a high voltage pulse. There are no other
controls. The cavity will resonate only as long as the cathode sees the high
energy. Perhaps you are referring to average power as opposed to peak power.
In which case you would be partially correct, but this is a function of
pulse length and pulse recurrent frequency (range selection). Normally, as
the pulse length decreases, the PRF increases proportionally, so even the
average power doesn't change too much.
Steve

"Marc Heusser" <marc.heusser.DeleteThis@byeheusser.commercialspammers.invalid> wrote in
message news:marc.heusser-6C3727.01023904012008@news.uzh.ch...
> In article <flji7g$rsi$00$1@news.t-online.com>,
> "Steve Lusardi" <stevenospam.DeleteThis@lusardi.de> wrote:
>
>> 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)
>
> Power is automatically reduced in all radars for closer ranges. And with
> the typical 50 microsecond pulse at short range a range of 15 metres
> around your antenna is blind anyway.
>
> The key issue is learning to adjust and read the radar, again and again,
> under good conditions blocking the radar operator's sight.
>
> There is an excellent simulator to train by the way from
> http://www.lightmaster.co.uk/Radar/LightMaster_Radar_Simulator_Mk2
> I found it when training for the Long Range Certificate, they have a
> simulator too for GMDSS DSC VHF, very useful to train distress calls.
>
> If had to start again, I'd first get the simulator, then go through a
> course, and only then select and buy the radar. I had the luck to get
> good advice from a trainer.
>
> From own experience in training for the radar certificate (Rhine at
> Basel, 200 meters wide, commercial ships up to 135 m long crossing at 30
> m lateral distance, bridges with support towers, narrow ports etc...),
> objects vary wildly in reflection, eg you may easily mistake a goose on
> the water or a duck flying by for a small rigid bottom inflatable power
> boat WITH a radar reflector (-> emergency stop of a 30 metre fire boat
> when cruising under radar only - real time simulation of dense fog
> or the next navigation mark with radar reflector at times. On the lake
> of Zurich we have ferries for cars - they have two parallel faces in
> their superstructure - this makes for a great multiple echo, even of
> your own boat ... the same can happen with oil storage tanks, regularly
> planted trees, a motorway bridge ... All this on a river quietly
> streaming. We were trained for failures too, be it rudder broken, radar
> failing or motor. It does give you confidence when you know what to do.
>
> I learnt too that you must not have a radar without VHF to call
> approaching vessels - on a river to call around bends, or negotiate
> crossing port to port or starboard to starboard crossing. AIS goes one
> step further as it broadcasts your position, heading, speed, size of the
> vessel, destination continously and includes the MMSI, so you can
> selectively call approaching vessels. Simrad has a unit for recreational
> boats.
>
> A narrow river is much more demanding than open waters in this respect.
>
> Knowing the waters (or at least having a good chart, preferrably
> overlaid) is key. A flat coast will be much closer as it seems because
> the reflections do not come from the waterline but from the next tree,
> house, boulders, ...
>
>> 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.
>
> You can get that on a small boat if you have the same 4' antenna.
> (They might have some digital filters that help some more, but you get
> most of it.)
> Actually on a super yacht I'd get a larger open array (IF I had the
> money for the yacht...) - at least 6', preferrably more.
>
>> 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
>
> There are other choices, Furuno is not the only one. Swissradar has some
> pretty nifty digital filters for example.
> (Check eg
> http://www.apple.com/downloads/dashboard/information/swissradar.html if
> you have a Mac - 3 weather radars map the current rainfall for the whole
> of Switzerland, 100 by 200 sm)
> Koden (Sitex) might actually try hard and be successful at it.
>
> On a small boat the combinations become important, as you might not have
> the space for a separate echo, chart plotter, radar and AIS display.
> A good balance of technical specs with space requirements and user
> interface is what you are typically after.
>
> My Simrad has a rather good auto setting on tuning/gain/etc, which for
> me is a big advantage as I expect other people to operate it with even
> less experience than myself. Along with the good chart overlay and a
> very flat unit to mount this tipped the scale. It does not have a MARPA
> on the other hand, but its trails work well as a substitute. The user
> interface is clear but not as nice as Mac OS X or my TomTom GPS for the
> street. (BTW their manual at
> http://www.simrad-yachting.com/Products/Leisure/Navigation-Fishfinding/CX
> 44-NavStation/Downloads/
> has a good explanation of radar operation and what sorts of displays can
> be handy - off centre display is one of them, what is behind you is less
> interesting than what's ahead).
> And I knew Koden as an electronic engineer, so I did not have any doubts
> there. Simrad's key expertise is actually echo sounders but their radars
> have a good reputation for a reason too. In yachting they are well known
> for their autopilots.
>
> On my small boat I could install a 4' open array antenna, which still is
> useful. I would not want anything less. Bear in mind also that larger
> antennas often have a smaller vertical beam, which is NOT what you want
> on a small boat, because it is rolling and you still want to see.
>
> It might be worthwile to check some of the articles referenced in
> http://marinedirectory.ybw.com/reprints/results1.jsp
> a search for "radar chart" from 2005-2007 in Category Electronics turns
> up this eg
> Buying a radar plotter Practical Boat Owner Jul 2006 p76-79 (4.00
> pages) etc
> before testing and buying equipment.
> The reprints are not free but most likely worth the money.
>
> HTH
>
> Marc
>
> --
> remove bye and from mercial to get valid e-mail
> <http://www.heusser.com>
 >> Stay informed about: Koden radars? 

In article <flkpmh$6am$00$1@news.t-online.com>,
"Steve Lusardi" <stevenospam RemoveThis @lusardi.de> wrote:

> Sorry Marc, you are not correct, power is not reduced at lower range
> selections. The transmitter tube is a magnetron, which effectively is a
> resonant cavity within a permanent magnet. It is excited by driving the
> cathode severely negative with a high voltage pulse. There are no other
> controls. The cavity will resonate only as long as the cathode sees the high
> energy.

Yes, I know that as an MSEE and anyone can verify it watching their
microwave oven that operates on the same principle. I did not want to
make the discussion more technical than necessary. I was referring to
average power to be precise.

> Perhaps you are referring to average power as opposed to peak power.
> In which case you would be partially correct, but this is a function of
> pulse length and pulse recurrent frequency (range selection). Normally, as
> the pulse length decreases, the PRF increases proportionally, so even the
> average power doesn't change too much.

Actually average power is reduced usually because the pulse length
decreases more than the pulse repetition frequency:

Data from Swissradar JFS364C that I currently have at hand:

Range 2 km 8 km 64 km
Pulse repetition frequency 3000 Hz 2000 Hz 1000 Hz
Pulse length 50ns 150 ns 600 ns
Average emitted power 0.6 W 1.2 W 2.4 W

So for a close range the average power is reduced to one quarter of the
power at long range.

Anyway most people would not care about power, and they do not have to
because the available units take care of that design decision.

Marc

--
remove bye and from mercial to get valid e-mail
<http://www.heusser.com>
 >> Stay informed about: Koden radars? 

Agreed Marc. My point that I was trying to make was that not only does the
6' antenna with its narrow beam help disciminate targets, so does higher
transmit power, even at short range, because of the increased echo strength
increasing the signal to noise ratio of the returning echo. This is very
important, especially in rough water, where the receiver needs all the help
it can get to discriminate a small, perhaps radar absorbing target from the
white caps. It is my belief that these two factors are the most important
points to be aware of when in the market for a new unit. To make my point
even stronger, a 25KW FR2125 Furuno will pick up a paper dixie cup at a 100
meters and an FR2115 at 12KW will not. Both radars are identical in every
respect except the transmitter. You may not attach much importance to this
ability, but the fellow I purchased my masthead rig from decided he would
change from a masthead rig to a fractional on his 70' aluminum sloop the
Dance II out of Southhampton in the UK. Right after the conversion, he set
out to Gibralter for some chartering. At 0200 off the coast of Portugal
making 7 knts he hit a partialy sunken shipping container that he never saw
on his 4KW radar with a 4ft radiator. The Dance II was lost. According to
Lloyds, this is a regular occurance and in a single calendar year hundreds
of containers are lost overboard. Maybe this ability is not important on a
lake, river or canal, but in the open ocean it certainly is.
Steve

"Marc Heusser" <marc.heusser RemoveThis @byeheusser.commercialspammers.invalid> wrote in
message news:marc.heusser-F75778.10441804012008@news.uzh.ch...
> In article <flkpmh$6am$00$1@news.t-online.com>,
> "Steve Lusardi" <stevenospam RemoveThis @lusardi.de> wrote:
>
>> Sorry Marc, you are not correct, power is not reduced at lower range
>> selections. The transmitter tube is a magnetron, which effectively is a
>> resonant cavity within a permanent magnet. It is excited by driving the
>> cathode severely negative with a high voltage pulse. There are no other
>> controls. The cavity will resonate only as long as the cathode sees the
>> high
>> energy.
>
> Yes, I know that as an MSEE and anyone can verify it watching their
> microwave oven that operates on the same principle. I did not want to
> make the discussion more technical than necessary. I was referring to
> average power to be precise.
>
>> Perhaps you are referring to average power as opposed to peak power.
>> In which case you would be partially correct, but this is a function of
>> pulse length and pulse recurrent frequency (range selection). Normally,
>> as
>> the pulse length decreases, the PRF increases proportionally, so even the
>> average power doesn't change too much.
>
> Actually average power is reduced usually because the pulse length
> decreases more than the pulse repetition frequency:
>
> Data from Swissradar JFS364C that I currently have at hand:
>
> Range 2 km 8 km 64 km
> Pulse repetition frequency 3000 Hz 2000 Hz 1000 Hz
> Pulse length 50ns 150 ns 600 ns
> Average emitted power 0.6 W 1.2 W 2.4 W
>
> So for a close range the average power is reduced to one quarter of the
> power at long range.
>
> Anyway most people would not care about power, and they do not have to
> because the available units take care of that design decision.
>
> Marc
>
> --
> remove bye and from mercial to get valid e-mail
> <http://www.heusser.com>
 >> Stay informed about: Koden radars? 

In article <fllv08$kdd$01$1@news.t-online.com>,
"Steve Lusardi" <stevenospam.TakeThisOut@lusardi.de> wrote:

> Agreed Marc. My point that I was trying to make was that not only does the
> 6' antenna with its narrow beam help disciminate targets, so does higher
> transmit power, even at short range, because of the increased echo strength
> increasing the signal to noise ratio of the returning echo.

It may - if the noise is coming from an external source. If the noise is
the water reflecting the transmitter's pulse, it probably does not help,
or does it?

> This is very
> important, especially in rough water, where the receiver needs all the help
> it can get to discriminate a small, perhaps radar absorbing target from the
> white caps. It is my belief that these two factors are the most important
> points to be aware of when in the market for a new unit. To make my point
> even stronger, a 25KW FR2125 Furuno will pick up a paper dixie cup at a 100
> meters and an FR2115 at 12KW will not. Both radars are identical in every
> respect except the transmitter. You may not attach much importance to this
> ability, but the fellow I purchased my masthead rig from decided he would
> change from a masthead rig to a fractional on his 70' aluminum sloop the
> Dance II out of Southhampton in the UK. Right after the conversion, he set
> out to Gibralter for some chartering. At 0200 off the coast of Portugal
> making 7 knts he hit a partialy sunken shipping container that he never saw
> on his 4KW radar with a 4ft radiator. The Dance II was lost. According to
> Lloyds, this is a regular occurance and in a single calendar year hundreds
> of containers are lost overboard. Maybe this ability is not important on a
> lake, river or canal, but in the open ocean it certainly is.

I wonder if he would have caught it only because of a more powerful
radar. Anyway, containers are a major danger, and I would not want to
hit one.
I guess digital signal processing can make more of a difference, but
this is unfortunately only available at a price.

Marc

--
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 >> Stay informed about: Koden radars? 

In article <flji7g$rsi$00$1@news.t-online.com>,
"Steve Lusardi" <stevenospam.DeleteThis@lusardi.de> wrote:

> 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.

Ok Steve, Please tell us all about why this would be important.
Actually, the Vertical Beam-width of a ANY Slot-line Radar Antenna, is
NOT related to the length of the Antenna, at all, but IS related to the
design of the Slot-line shielding, and slot-line position inside the
shielding. If you look at the Furuno Antenna Spec's you will notice
that ALL the Slot-Line Antennas, have a 25° Vertical Beam-width, and
have had since Furuno first Started importing their products to the
USA, back in the KRA-121 days.

--
Bruce in alaska
add <path> after <fast> to reply
 >> Stay informed about: Koden radars? 

In article <flkpmh$6am$00$1@news.t-online.com>,
"Steve Lizard" <stevenospam.DeleteThis@lusardi.de> wrote:

> Perhaps you are referring to average power as opposed to peak power.
> In which case you would be partially correct, but this is a function of
> pulse length and pulse recurrent frequency (range selection). Normally, as
> the pulse length decreases, the PRF increases proportionally, so even the
> average power doesn't change too much.
> Steve

Well, Not Exactly Steve....as the Pulse Length decreases the Peak Power
in each Pulse decreases, and the Effective Radiated Power for each
Pulse, corresponds directly to the Peak Power of the Pulse, as does
distance that pulse can travel, and be detected after reflecting back
from a target. A Marine Radar has much better Target Resolution at
Shorter Ranges, due to higher Pulse Repetition Rates, but if you do the
Math, you will see, even the Average Power is somewhat Higher for the
Longer, but less Frequent, Pulse Lengths. Because Radars use RF, they
are slaves to the Inverse Square Law, and at Short Ranges, it isn't
the Peak Pulse Power, that is the Limiting Factor, for either Resolution,
or Minimum Effective Target Acquisition.

--
Bruce (semiretired powderman & exFCC Field Inspector for Southeastern Alaska)

Bruce Gordon * Debora Gordon R.N. Bruce's Trading Post
P.O. Box EXI Excursion Inlet South
Juneau, Alaska 99850 Excursion Inlet, Alaska 99850
AL7AQ * KL7WJ www.btpost.net www.99850.net
 >> Stay informed about: Koden radars? 

Bruce,
The 20 degree fan does prevent the helmsman on my boat from being in the
path of heavy radiation and the sidelobe power outside that 20 degree fan
is -28 DB and that is important to me. The specs for Furuno radiator
XN20AF/6.5 Beamwidth (H) 1.23 degrees, Beamwidth (V) 20 degrees. On the
other hand their S band antennas are 25 degrees like the SN30AF. In point of
fact all the Furuno X band radars are 20 degrees, not just the 6 footer,
which is in line with your statement that all Slot-Line anennas have the
same vertical fan, but the number is 20 for X Band not 25, but I do recall
that antennas by other manufacturers are 30 degrees.

By the way, I did listen to your advice last year and scrapped the 6 KW
Decca and acquired an FR2125BB.
Steve

"Bruce in alaska" <fast DeleteThis @btpost.net> wrote in message
news:fast-02DC90.12492804012008@netnews.worldnet.att.net...
> In article <flji7g$rsi$00$1@news.t-online.com>,
> "Steve Lusardi" <stevenospam DeleteThis @lusardi.de> wrote:
>
>> >
> Ok Steve, Please tell us all about why this would be important.
> Actually, the Vertical Beam-width of a ANY Slot-line Radar Antenna, is
> NOT related to the length of the Antenna, at all, but IS related to the
> design of the Slot-line shielding, and slot-line position inside the
> shielding. If you look at the Furuno Antenna Spec's you will notice
> that ALL the Slot-Line Antennas, have a 25° Vertical Beam-width, and
> have had since Furuno first Started importing their products to the
> USA, back in the KRA-121 days.
>
> --
> Bruce in alaska
> add <path> after <fast> to reply
 >> Stay informed about: Koden radars? 

In article <flo595$4kn$01$1@news.t-online.com>,
"Steve Lusardi" <stevenospam DeleteThis @lusardi.de> wrote:

> Bruce,
> The 20 degree fan does prevent the helmsman on my boat from being in the
> path of heavy radiation and the sidelobe power outside that 20 degree fan
> is -28 DB and that is important to me. The specs for Furuno radiator
> XN20AF/6.5 Beamwidth (H) 1.23 degrees, Beamwidth (V) 20 degrees. On the
> other hand their S band antennas are 25 degrees like the SN30AF. In point of
> fact all the Furuno X band radars are 20 degrees, not just the 6 footer,
> which is in line with your statement that all Slot-Line anennas have the
> same vertical fan, but the number is 20 for X Band not 25, but I do recall
> that antennas by other manufacturers are 30 degrees.
>
> By the way, I did listen to your advice last year and scrapped the 6 KW
> Decca and acquired an FR2125BB.
> Steve
>
> "Bruce in alaska" <fast DeleteThis @btpost.net> wrote in message
> news:fast-02DC90.12492804012008@netnews.worldnet.att.net...
> > In article <flji7g$rsi$00$1@news.t-online.com>,
> > "Steve Lusardi" <stevenospam DeleteThis @lusardi.de> wrote:
> >
> >> >
> > Ok Steve, Please tell us all about why this would be important.
> > Actually, the Vertical Beam-width of a ANY Slot-line Radar Antenna, is
> > NOT related to the length of the Antenna, at all, but IS related to the
> > design of the Slot-line shielding, and slot-line position inside the
> > shielding. If you look at the Furuno Antenna Spec's you will notice
> > that ALL the Slot-Line Antennas, have a 25° Vertical Beam-width, and
> > have had since Furuno first Started importing their products to the
> > USA, back in the KRA-121 days.
> >
> > --
> > Bruce in alaska
> > add <path> after <fast> to reply

So your inference is that "IF" a RADAR Antennas Main radiation Lobe
intersects with where a human stands, that this is somehow "Bad",
or dangerous? Hmmm, have you ever done the math, to calculate the
Power Density of the RF Energy at the face of the antenna, at a
distance of twice the Slot-Line Antenna Length, or even at 20 Ft
from the Antenna? Then consider that it is Rotating, and the human
is only in the Radiation Field less than 5% of the time. Add to that,
the fact that for non-ionizing Radiation, it is Average Power, and not
Peak Power, that creates harm to biologics. What is the Average RF Power
Output from this Xband Marine Radar? As in all RF Radiation, Marine
Xband Radar Energy follows the Inverse Square Law.

Your concerns, however irrational, are yours, to deal with, but the Math
doesn't compute in your favor, here.

Bruce in alaska

--
Bruce in alaska
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 >> Stay informed about: Koden radars?