Is there a Radar techie out there?

[Joe_Cole]

I'm interested in getting a CARD (Collision Avoidance Radar Detector) which could be useful in poor visibility. As a relatively cheap device it is limited but may be helpful.

However it occurs to me that it is possible now to get Radar detectors which are designed to warn about the presence of police Radar Speed Guns. Looking at various websites these seem to be able to detect Radar at up to 2 miles distance, and they claim to operate at a full 360 degrees. They don't give any directional indication but at least they could warn you that there is something out there!

With a starting price of under £100 they appeal.

The question is this. Would they detect shipping Radar, or does this work on a different frequency?

Regards

Joe Cole

 

[Chris_Stannard]

Regret I have thrown my reference books away having retired. Frequencies are allocated by International convention and if my memory serves me right the following would apply. Merchant ships have radars in one of two bands, Centemetric (used to be known as X Band) and metric (used to be known as S Band). The frequencies are chosen for windows in the atmosphere, in things like water vapour absorbtion of radiation to give good performance. Range scales are usually out to about 24 miles on X Band, which is incidentally the frequency used by most yachts radars, and 48 on S Band, which being lower in frequency bends round the earth a bit better.
The police do not require a great range, and if you can detect their transmissions at 2 miles they would in theory be able to detect you at about 1.25 miles. however they are usually only working at 50 - 200 metres. They also need a very narrow beam, to avoid getting detections for other vehicles in the vicinity. Hence they use a much higher frequency, somewhere in the high millimetric band, because the beam width is dictated by the size of the antenna and the frequency, the bigger the antenna the smaller the beam and the higher the frequency the smaller the beam.
Short answer therefore is that the speed gun radar detector is unlikely to work. If you go to the advertised, purpose built radar detection device for yachts be careful as it will only detect one band, usually X Band, and there are quite a lot of merchant ships with S Band these days. Thus you will be aware of a fellow yachtie, but not necessarily of a merchant man. Incidentally your radar reflector will not be use if the merchantman has S Band, and in my opinion they are pretty useless in any case. You would need something much bigger than the current designs to give the right amount of reflection all round and you copuld not carry it.

If you are seriously worried about being caught out in fog my advice would be do not waste your money on half baked devices but save up for a cheap radar. If it gives you six miles on a merchantman, that is enough to get out of their way, and it will also give you about a mile on other yachts. The management insisted we bought one after 10 hours in fog including nearly being run down by a rampant fishing boat. And it was a nice sunny day when we started.

Remember the normal rules for Collision avoidance do not apply in fog since vessels are not in sight of one another. So it pays to give way and early.

Safe sailing






Chris Stannard

 

[jfkal]

Fully agree. Would not work (

 

[HaraldS]

Not likley to work.

Police radar usually works at much higher ferquencies, so that they get better accuracy through the dopller shift. Car radar detectors have been tuned to be very selctive on frequency, to cut out false alerts, so they may not respond at all to a ship radar, even though there is some overlap in the X-band.

As has been pointed out, ship radar works in two bands: S-band at 3.0 GHz (the band is from 2GHz - 4GHz), and X-band at 9.4 GHz (the band is from 8GHz - 12GHz).

Police radar works at X-band 10.5 GHz (very old units, but most detectors still cover it, but might be selctive enough to exclude 9.4GHz), K-Band 24.05 - 24.25 GHz, Ka-Wide Band 34.2 - 35.2 or Ka-super wide in the range of 33.4 - 36.0 GHz.

In short, the better the car detector, the less likley it will pick up a ships radar.

The C.A.R.D. system cover the full range from 3GHz to 10GHz, not very selective. I have heard it quite often gives false alarms. If you are navigating in desne fog in a busy area, any detector will just keep beeping, telling you that you are surrounded by dangers. Not much of a help. Just way out, when you may pick up just one radr signal, it would give you a wague idea where to look.

Like Chris suggested saving up for a real radar should be the first choice. They start at about twice the price of the C.A.R.D. system.

Remains the argument that way out on the ocean you may not want to run your radar to conserve power and reduce wear, but be warned if something crosses your path. For that purpose C.A.R.D. would be ok, but today I would choose an active radar reflector, that combines detection and possible alert, with sending back an amplified echo, making your appear more prominent on other ships radars.

BUT, not too long ago I read an interview with a commercial tanker captain, who claimed that many of the big ships turn off their radars once they are way out into the ocean, some he claimed had orders to do so to reduce wear of the expensive equipement. He continued to say that they know of other big ships around through the AMVER reporting system!

 

[graham]

I know this is not much use to you now but just as a matter of interest by 2003 all new ships will have to have aShip Identification Transponder. All existing ships have until 2008 to comply.

This is primarily for use by port control stations to identify vessels in their waters.

Linked to GPS and a chart plotter it is amazing as it gives the position course speed and name on the screen.

I amagine that a detector suitable for smallcraft will appear on the market as time goes on.

Apparently any ship entering a UK port after it becomes compulsory will be detained in port until one is fitted.

 

[Joe_Cole]

Ah well! It was worth a try.

Thanks for your replies.

Joe Cole