Positioning of radar dome: danger when transmitting?

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NealB

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I've recently bought a 2nd hand Furuno 1621 radar, and am thinking about where to mount the dome (on the elderly motor boat).

The easiest place is on the small mast, where it will be about 12 feet in front of the helmsman, and about 1 foot above his or her head.

Would this mean we get microwaved brains?
 
This comes up regularly and solicits a variety of opinion on the subject. Its the height that would concern me as at that height you will be directly in the beam. Actually you might be safer with it more directly overhead from that point of view as you might then be under it... dunno..
Personally I would try to get it higher. A short stainless steel pole is sometimes used for a transom mount. Also the higher you can get it the further it will see within reason (lets not start another post about increased sea clutter, I said within reason!)
 
Yes, getting it higher, or moving it further aft, would take heads out of the vertical beam 'cone' area.

I just wondered if the microwave engineers on here (or any others in the know) might be able to tell me that, from 12 feet, a small boat radar is not a risk.
 
I think the problem is no one really knows. There are those who say using a mobile phone regularly inches from your brain is a risk. Living under pylons etc.... risk? Most radar sets come with a warning to site away from your nut, but is that just a jobsworth copout? Dunno. I don't think you will get a clear consensus about what is safe and what is not.... To me the argument resolves itself when I look at the dipping distance. You will still see big ships low down of course but it helps greatly to see smaller targets if the scanner is a bit higher. Yo do need some sort of mast support though.
 
absolutely- the guidelines for this sort of frequency are more concerned with heating effects - you would have to try very hard to exceed these with a small radar set (don't forget the 2Kw or whatever is the pulse energy not a constant figure)- but I would always play it safe after all asbestos, PCB, Smoking, even arsenic were all at one time believed to either be good for you in small doses or harmless.

So as stated before - move it either higher (possible guying issues) or have it almost directly overhead; they are designed to emit very low levels underneath. In addition metal (even thin foil) will block it dead.
 
You're both convincing me to err on the cautious side.

I should be able to rig it pretty well directly ovehead, with just a bit of stainless tubing fabrication required. That'll also make wiring runs easier to hide, anyway.

Thanks for your thoughts.
 
Although height will give you a greater theoretical range, this is not likely to be significant and I pick up ships at 18 miles from a stern pole & 2Kw. By all means put it on the mast, but it doesn't have to be unnecessarily high. I have heard anecdotal reports of higher radomes giving rise to more sea-clutter.
 
As a sometime microwave engineer, I'm reluctant to even put radar on my boat. You certainly do not want to be in the main beam. Just my personal take on things, having worked with some ex Plessey Radar people. Very little proper science to back this up, but why take chances with things we don't understand?
In lab conditions we generally take 10milliwatts as a 'safe level' to radiate, and don't shine it at your eyes or reproductive bits.
It's probably like living under power lines- OK for 'other' people.
What does the manufacturer say?
 
[ QUOTE ]
Yes, getting it higher, or moving it further aft, would take heads out of the vertical beam 'cone' area.

I just wondered if the microwave engineers on here (or any others in the know) might be able to tell me that, from 12 feet, a small boat radar is not a risk.

[/ QUOTE ]

12 feet is more than the red painted danger cirlce painted on the deck of warships around microwave emmitters so I'm sure it will be fine for a little Furuno!
 
This has come up so many times before, so I'll summarise.

No problem. You'd need a far more powerful radar to cause concern. If the radars on boats were potentially harmful, there would be hoards of boaters in US doing claims
 
When a radar is transmitting it rotates about 20 rpm, during this time it listens for 99.9% of the time, so is not transmitting.

The power of radar is far more than domestic microwaves but the burst of energy during transmit is so short that it poses no danger unless you are near enough to touch the radome, then there is a small risk if you stay there long term.

My radar is at head height behind the helm and I never worry about it.

I don't see a problem with the positioning you describe.
 
[ QUOTE ]
I'll summarise.
No problem.

[/ QUOTE ]Hmmm...
If you mean that just by travelling by car on a motorway we're taking greater risks, you're probably right.
But no problem at all, who can actually say that safely?
Fwiw, I'm happier with my radome standing much higher than myself.
 
[ QUOTE ]
As a sometime microwave engineer, I'm reluctant to even put radar on my boat.

[/ QUOTE ]

Hmmm -Interesting. I once knew a high ranking government microwave expert who refused to have a domestic microwave oven in his house.

What do you guys know that we don't.
 
"Hmmm -Interesting. I once knew a high ranking government microwave expert who refused to have a domestic microwave oven in his house.

What do you guys know that we don't".
-------------------------------------------------

An excellent question: anyone prepared to tell us?
 
[ QUOTE ]
Hmmm -Interesting. I once knew a high ranking government microwave expert who refused to have a domestic microwave oven in his house.

What do you guys know that we don't.

[/ QUOTE ]

I was on a dangerous goods course with an instructor who in his pevious 'life' had discovered and had an isotop named after him ..So I assume he knew something about these things..He would not have an MW in the house (Quote..if you have to use one keep 3 mtrs away and leave the doors open!)...also, although he had a mobile ph he kept communication to a ..yes/no/ see you later basis.

Regds Nick
 
You could actually calculate the amount of power arriving at your head by calculating the mean power transmitted (Mean Power= Peak Power X Pulse Width X Pulse Repitition Frequency), you would need to do this for each of the pulse width settings on your set (actually the "worse" one: the longest one is the one that matters). Then calculate how long the beam will be on your head for a scanning radar of xx r.p.m. (24 seems a typical figure IIRC) and for an "X" degree horizontal beamwidth ( 5 or 7 degrees seem typical). Then calculate the power arriving at your head by applying the inverse square law to the distance of your head from the radar transmitter horn beam centre. All this will give you a power flux density at your head; compare this with the government specs for safe microwave usage .......... note this is different for different countries (apparently if you're Russian you can withstand absorbing a lot more power!!!!).

But ........... after working with radars and satellite station transmitters for the last 40 years (how sad can you get!!!!), then I would mount mine so that the 25 degree vertical beamwidth passed over the head of anyone standing on the bow of the boat and this would mean about 3 or 4 metres up the mast.

But .......... I don't have a radar!!!!!!!!!!!!!!! so this is only theory.

Out of interest I once attended a symposium on antennas organised by the IEE and one of the speakers described a test method for the radiation patterns of mobile phone antennas; one of these tests involved putting a "dummy" head next to the phone and measuring the antenna patterns. The head cause "a significant affect" on the patterns but the speaker was unable to quantify these affects due to contractual arrangements with the phone company !!!!
So, you interpret this as you choose ........... but I like to keep my head out of radiation areas (the other important parts of my body are past their use by date!!).

Alan.
 
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