Health Concerns w/regards to Radar Height

[VeniVidi]

I understand the pro's and con's of Radar on the Mast vs. on A stern Pole Mount vs. Backstay, etc.........

But does *anyone* have a concern with the Radar so low that it might cause health related issues for anyone on the foredeck?

I guess this is my *biggest* worry..........

Should I be? ......any Radar engineers/technicians out there?.....If so, do you have any children?....;-).

Tom


Living is about making mistakes………Dieing is about wishing you made more.

 

[numenius]

Suggest you do a search on the forum - this very subject was discussed in some detail about a week ago. I seem to recall that the consensus was that as long as it WAS above your head height, it did not really matter by how much (from a safety point of view) . Presumably within the length of a boat, it's still in a pretty tight band on the horizontal plane. Certainly my own radar's manual only refers to distance from you on the horizontal plane and does not refer to a minimum safe height above you at all.

http://members.lycos.co.uk/boaty1965/index.htm

 

[pvb]

Raymarine\'s advice is...

Raymarine say that "Due to the relatively low power of leisure radar, concerns over harmful transmissions are generally not considered to be a problem as long as people are a few feet from the scanner unit (about 3 feet) and the scanner is positioned above eye level."

The cynical might think "Well they would say that, wouldn't they?", but, bearing in mind Raymarine's position in the radar market, and their extensive sales in the safety-obsessed USA, we can probably trust their advice.

 

[Guest]

Your radar sends out microwave pulses of very short duration but of 1kw or more power. More than your microwave, but not continuously. Way more than your mobile phone, but remember the fuss about hand held phones a year or two back?

Personally, I dont see the point in taking any risk. After all, at one time the medics said smoking was good for you!

Stick it up the mast, and fry seagulls instead.

 

[brian_neale]

A Raymarine 2KW radar takes less than 36 watts average while operating (may be significantly less - cannot remember exact figures). Of this, the display takes maybe 12W, the scanner motor maybe 12W, leaving 12W average for the actual radar. X band radar is not like microwave ovens, designed to run at a frequency which optimises absorption by water molecules, so relatively little would be absorbed by the body. So, my guess is about as dangerous as the radiation from a masthead light. Well, not far off.

Yes, a simplistic analysis, but I think that the overall message is not to get too worried about the 2KW peak power - the actual pulses are extremely short, so the average power is miniscule.

 

[johnsomerhausen]

When I brought my radar which hasd stopped working to an electronics firm in Sydney (Nova Scotia), I was surprise at the lack of precautions the technician was taking and asked him if the radiations weren't harmful so close by the scanner. He replied that "these small radars don't really bite and if I work too long on them, my eyes begin to water and that's a sufficient warning time..."
Since it was his health that was in the balance, I'd trust his opinion.
john

 

[HaraldS]

I think that even a somewhat more sophisticated calculation gives no reason for alarm.

Like all of you I was concerned about the same issue and sat down for some calculations:

My radar is mounted on a post and is 2.6 meters above deck. It has 4kW pulse power.

It's vertcal opening angle is 22 degrees, horizontal 2.5.

Simple trigonometry says that you will need to be 4.1 meters away from the radar post, before the beam starts scratching your hair, if you are 1.8 tall.

At that disrance the radar aperture has grown to be 1.6 meters (verical) by 1.4 meters (horizontal); this translates to 2.2 square meters.
When the signal exited the antenna, the opening surface of the 3 foot scanner it was 0.06 square meters.

So by now the field density has gone down by a factor of 36.

At it's most powerful setting, the radar sends 750 pulses of 0.7 microseconds per second, so a very smal duty cycle. The pulses are 4kW. If you multiply that with the dutycycle you get an average transmitt power of 2.1W!

Combine this low average with the reduction from the distance, and it becomes easy to see that microwave tissue heating, or boiling eyeballs, are far from possible.

Now of course nobody knows of other effects, that may relate to pulse power and I'll avoid standing in the beam just in case, but that concern would have to be a lot higher with a cell phone.

 

[Chris_Stannard]

The quick answer is that there is unlikely to be a problem with a mast mounted radar, there is more chance of a problem with a pole mounted radar at the stern to the cockpit occupants, but the probability of this is not high.
First as already stated a radar transmits short high energy pulses, which puts it in a different league to your mobile phone. If you think about it you hold your mobile phone alongside your brain for minutes at a time with the transmit button held down. The transmit button in this case is a audio switch with a dwell time so that it stays on during the gaps in your speech. The rod aerail puts most of the power into a flat field and your brain covers an arc of about 90 degrees. So your brain is being fried by up to 1.25 watts of microwave energy (1/4 of up to 5 watts) all the time you are speaking. Incidentally your phone may adjust its power level to meet current conditions, so it will step its power up when you are out in the country and down when you are in the town close to a base station.
What about the radar. Firstly the beam width of the average radar in a boat is about 8 degrees in the horizontal plane. This is because the antenna is quite wide and the beam width is dependant on the width of the aperture. In the vertical plane the aperture (antenna) is narrow and therefore the beam is wide, about 30 degrees. However the beamwidth is measured to a point where there is still enough energy to give a reasonable chance of a detection being made (I wont go into dBs), but this is much lower than the highest power levels which are in the beam centre in both the horizontal and vertical planes. In simple terms if you put your antenna 5 metres up the mast you would need to be 18 metres away from the mast before you got to the half power point on deck. So the guys on the foredeck and in the cockpit are okay.
As the beam sweeps round, typically at about 24rpm, you will get a burst of energy for about 2 % of the time for each revolution. This equates to a total of about 1.35 seconds per minute. But the radar transmits in short bursts. leaving enough time between each pulse for the beam to get out to well beyond the maximum range of the set, and back to the receiver. So the exposure drops. If you think about it the radar draws about 6 amps at 12 volts, which equals 72 watts for a 2 KW output. As the set is probably 70% or less efficient this gives and average power output of about 50 watts,which is 10 times that of the mobile phone. A further rule now comes into play which says the power falling on a given area is inversley proportional to the square of the distance. So if the power at 1 metre is X at two mwtres it is 1/4 X and at 5 metres it is 1/25 X. As you can see hold your phoneagainst your head and get full whack, the radar is metres away, so the power is falling rapidly. This explains why the techy in Newfoudland was getting an affect after working close to radars all day.

If you do not understand all this rubbish, and although I have tried to put it simply, but am not sure it is comprehensible to the non technical, the best point is that product liability litigation in the USA makes manufacturers very careful about ensuring they cannot be sued. So the radar is as certain to be safe as they can ensure.

Lastly, I served in the navy with high power radars, and with a wave guide, which took the power up to the antenna, running through my cabin. It was not suposed to leak but there was a loss in the waveguide. I still had children who are perfectly normal.

In my view the risk is so low it is haard to measure whilst the benefit is enormous. Try being caught out in the channel in fog.


Chris Stannard

 

[gtmoore]

A very comprehensive post but just to be pedantic, GSM mobile phones have a maximum power output of 2W (1W for GSM1800). This is normally nearer 100mw as you quite rightly point out due to adjustments made by the phone itself (under command from the base station in use). A GSM phone also uses 1 of 8 timeslots allocated per frequency so the effective power is 1/8th of this. However, it is this pulsing (sometimes heard when a mobile is near an audio speaker) that has caused some health concerns

By far the biggest reduction though is by distance from the transmitter as you say and mobile phones are the main culprit here. Just for interest, as I understand it, your average mobile phone mast has an output of around 25W.

Gavin Moore

 

[Guest]

Surely the point here is not the precise level of wattage per sq mm, but the long term effect of microwave radiation on cell structure in the human body. Given the relatively recent intro of mass manufactured sources of electromagnetic radiation ( how many radars were there 10 years ago? or mobile phones?) we dont have long experience to rely on. And is medical science more reliable in this area than it was in bse, f&m etc.

It seems to me only sensible to avoid the radiation if you dont have to expose yourself to it. Stick it up the mast!

And as for the US product liability argument - asbestos!

 

[Guest]

Some years ago, when I was involved with radar transmissions (high power), I understood that the potential problem involved the heating effect on body tissues, and everything was relative. i.e. transmission strength, position in the beam and distance from the point of transmission. The effect is most dangerous to body tissues where blood circulation (cooling effect) was minimal. Those tissues are located in the eyeballs and (for men) the testicles. The effect on ovaries was not mentioned. An important point is that the effect is said to be CUMULATIVE so that, although each individual exposure may seem to be innocuous, over a number of years the effect may be significant
For small boat radars, the transmitted strength is relatively very small, the beam width on radars up to mid price range, is relatively wide. Overall, the danger would appear to be fairly small. However, it would seem to be common sense to ensure that the antenna is mounted at a higher level than head height for the tallest crew member, or passenger, standing on the highest deck height.

<P ID="edit"><FONT SIZE=-1>Edited by achillesheel on Wed Apr 10 23:18:38 2002 (server time).</FONT></P>