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» Online Classroom   »   » Public Discussion of Marine Radar   » Mounting height for safety?

   
Author Topic: Mounting height for safety?
Michael Delorenzo


 - posted July 12, 2005 01:10 PM      Profile for Michael Delorenzo           Edit/Delete Post 
I want to make sure anyone working on the bow of my 35 ft sailboat is completely safe from radiation from the radome. I calculate at 35 ft, radiation leaving the radome (mounted 10ft high) heading down at an angle of 12.5 deg will hit a 6 ft person standing on the bow (from about the knees up). I don't know how to account for distance from the radome. Or is there no problem here?
Any help here would be much appreciated!
Thanks.

David Burch


 - posted July 12, 2005 03:12 PM      Profile for David Burch           Edit/Delete Post 
This has been the way many of us thought about this exposure, but the recent research that went into the Radar for Mariners book (summarized in Figures 7-20 and 7-21)leads me to think that the beam remains elevated for a larger distance off than we might have otherwise guessed.

In other words, the beam emerges from the antenna with about the same profile as the (internal) antenna face itself and stays in this form for some distance (called the near field range). That distance depends on the antenna width and the radar wavelengh (3 cm in this case).

Please read through that section of chapter 7 on radiation safety, including the sample computation of an actual antenna configuration. I think you will find that a typical smallcraft scanner mounted on the backstay or quarter post would not pose a radiation hazard to anyone at the bow or mast.

The book also includes the recommended maximum exposure levels from several agencies. And although they do not agree with each other on maximum levels, it seems you would be safe here even with the most conservative.

The main hazard with small craft radar exposure is close to and inline with the antenna -- especially if you stop the rotation and keep the transmitter on, which is not an accessbile mode in modern units.

A nutshell summary of the discoveries presented in the book is, we are generally exposed less than we might have guessed when away from the antenna and not inline with the scanner, and rather more exposed when up close and inline with it -- a place that most mariners know intuitively is not a good place to stay for any extended period. (It is the job of the skipper or navigator to inform crew or guests of this situation if it appears they to not know this.)

Radiation exposure from small craft radar is clearly a topic worth more discussion, and we hope that the book provides a foundation upon which that discussion can build.

From: Starpath, Seattle, WA


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