radar scanner

[chrisb]

Further to my question regarding marpa - the standard scanners have either 24 ml or 48 ml range. It seems to me that as the effective range for spotting shipping[main reason for fitting] is perhaps 10 miles there is little point in fitting the more powerful scanner . reasons would be extra weight up the mast increase power consumtion and extra cost. you guys Im sure will have experience and opinions.

<hr width=100% size=1>

 

[Talbot]

The only reason for having the extra range is if you will be continuously making a landfall where there are very high cliffs. Otherwise no point at all. You are unlikely to see even an American Aircraft Carrier at 24 miles and that is one of the tallest vessels at sea - In fact anything over 16 miles is only of occasional use. Greater bearing accuracy from a larger scanner does have its advantages, but this leads to greater weight and wind resistance and higher power consumption!

<hr width=100% size=1>

 

[boatmike]

Don't believe for one minute that you will get a reliable echo return at 48 miles from a so called 48mile radar! (Although I bet that starts a flood of replies from people who say they can) For many reasons you won't, not least that you can't mount the scanner high enough to see that far over the horizon.
What is important is that the bigger the scanner the greater the power of the pulse. Power is good. Especially in rain or fog where it will "punch through" in conditions that will knock out an underpowered set or reduce it's range considerably.
Also remember for ARPA to work accurately you really need a high quality giro compass. A fairly average fluxgate will work but the bearings will not be accurate enough to give a reliable collision warning. An unreliable collision warning or worse no warning when you should have one is worse than mark one eyeball on the screen. There is such a thing as a radar assisted collision don't forget.
It is better to be unsure and suitably cautious than to be sure and wrong in my opinion!


<hr width=100% size=1>

 

[Jools_of_Top_Cat]

You will also find, but not definately, that the scanners size is relative to the power; at least that is what I was finding at LIBS.

16 mile = 15" scanner
24 mile = 18" scanner

and so on, the bigger the scanner the smaller the bandwidth, this is better for distinguishing small close together targets such as channel markers. So I would guess the rule of thumb would be to fit the biggest dish your boat can comfortably handle. I have never seen though an 18" scanner rated at more than 24 miles, but they might exist.

Hope this makes sense!

<hr width=100% size=1>Julian

<A target="_blank" HREF=http://www.topcatsail.co.uk>Top Cat Homepage</A>

 

[john_morris_uk]

I know nobody loves a smartarse but surely you mean 'beamwidth' and not 'bandwidth'.

You are correct when you say that the advantages of a bigger scanner are reduced beamwidth which gives an increased ability to distinguish targets that are close together.

However the higher power helps even at low range because radar returns are so fickle.

<hr width=100% size=1>

 

[Jools_of_Top_Cat]

doh! thank you for pointing out my error, I had not long been in from work, had a noise fault across the whole bandwidth of a receiver and had it on my brain. I fixed it just before finishing by changing a mixer, bloody anoying little beasts.

Fairwinds......

<hr width=100% size=1>Julian

<A target="_blank" HREF=http://www.topcatsail.co.uk>Top Cat Homepage</A>