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Thread: Radar placement

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    Default Radar placement

    I have removed the radar arch from tolly flybridge because it won't trailer with it on.My question is what are the repercusions if I remount the radar on the front of the flybridge?. Do I lose 180 degrees of the coverage? Is this loss a big deal? Dan

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    Member HuntKodiak's Avatar
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    Default Blind spots

    Where ever you place the radar, all obstacles in the same plane as the radar will block the radar emission in that direction. The result will be a sector(s) of area that you won't detect any objects. On large vessels (my experience is with Coast Guard cutters), there is often a mast that is aft of the radar which creates a blind sector behind the boat. The farther away from the radar that you can make the obstacle, the smaller the sector blind area.

    Also, putting the radar directly on top of your cabin can cause a blind area close to your boat. It just depends on how close you put the radar to the edge of the mounting surface. That's why most people elevate the radar pedestal at least a little bit.

    Of course, if one has to choose an area to be blind, behind one's boat is preferred. An exception to this is if you plan on having any helicopters approach from the rear to land on your flight deck.

    Probably not a big concern for most of us chatting on this board.

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    Member Maast's Avatar
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    Default 3 things to think about

    There are three things you'll need to think about if you mount the radar on the front of your flybridge.

    1. You're going to lose half of your coverage
    2. The radar emissions will play havok with your electronics unless you blank out that portion of the sweep (dont know if your radar has blanking capability), and even then your back and side lobes will still be a problem.
    3. You've got a rotating high power microwave oven type beam now at head level for anybody who goes forward.

    You might want to look at the new BR24 broadband radars, they put out an couple of orders of magnitude less power, less than a cell phone, they're spendy though, and only a few types of displays can handle their output.

    When a radar emits you've got the main beam (lobe) coming out of the antenna, but you've also got smaller side and back lobes that are emitted, the antennas and displays can correct/minimize the side and back lobes effect to an extent but can't eliminate it entirely, even phased array radars have back and side lobes.

    Microwave ovens came about because an early radar researcher noticed a candy bar melting in his pocket. Eyeballs and testicles are particularly vulnerable to getting cooked by radars (or high power radio antennas) due to their limited blood supply.

    Sorry about the radar lecture, I was a field-mobile scope dope (radar command and control) for 23 years.
    2696 Sea Raider Pilothouse
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    Default Ahhh the good old days

    Of dressing the new fish up in aluminium foil and having them stand on the bow to "calibrate" the radar.
    (over the loudhailer)

    "Now slowly raise your right arm...... hold it right there, point your left foot to the left more, thats right, hold it, tilt you head back a bit, good" etc.

    Best part is when we called the ship infornt of us so they could "calibrate" thiers too.....

    USCGC Tamaroa

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    Default

    Just wanted to second what Maast said, and add a bit more.

    You should look at what is on the same horizontal plane as the radar. Anything within 5 degrees or so of it will be a problem. Two specific things to look out for are people and GPS antennas. I have heard that if they are aligned, the GPS antenna will get ruined. Even if they are lower power, they emit microwave radiation, which is not good for people, so if you mount it where it would not be above head level, I would not be on the flybridge when it is running, and it is probabily not a good idea.
    2009 Seawolf 31'
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    Member Music Man's Avatar
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    Default

    [QUOTEJust wanted to second what Maast said, and add a bit more.[/QUOTE]
    How much power would it take to light a florescent tube?
    When seconds count, the cops are just minutes away.
    '08 24' HCM Granite HD "River Dog"

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    Member Maast's Avatar
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    Default

    I dont really know about the low power recreational marine radars, I'm guessing about 500 watts peak to peak.

    Funny you should mention the fluorescent tube thing, in garrison for a visual check to know when the radar was radiating we strapped a pole with a fluorescent tube to the radar van just below the main beam, it'd flash every sweep and that'd let us know not to get above 15 feet. Of course that radar put out a heck of a lot more power.

    Reading my earlier post I guess I should have been a more clear; mounting your radar on the front of your flybridge is a bad idea.
    2696 Sea Raider Pilothouse
    "Dominion"

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    Member HuntKodiak's Avatar
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    Default

    dpmimmack,

    As a result of some of these horror stories, don't get too paranoid. Would you be wise to place the radar pedestal above a height that would put people in the rotating beam? Sure. Why expose people to unnecessary RF waves?

    However, it's safe to say that the power of your radar is significantly less than the output power of the X and S band radars that were used aboard the Coast Guard cutters that I was on. We (the CG) were required to determine the radiation hazard zones for all transmitting devices, and and we had to mark these areas to keep people outside of them while the equipment was operating. For the two radars I mentioned (surface search and air search), it was not possible for someone to stand close enough to the rotating X band (smaller array & power) pedestal and exceed the permissable exposure levels. You would be physically struck by the array first. For the S band (larger array & power), the safe area was just outside the rotating array.

    However, if a tech were to stop the rotation of the array while the radar was still transmitting (part of an alignment procedure and sometimes a troubleshooting step) then it was possible to get exposed to higher levels than was safe. I can't remember the distance, but it still was pretty close....like maybe 10 feet or so I think. I can't remember the output power of those things, but I think it was around 30 or 40KW (30,000 watts).

    The other issue mentioned about damaging other equipment, yes, that should be a precaution because sensitive devices like a GPS antenna could be damaged by spikes in voltage caused by the RF. And even if not damaged, your radar could definitely cause some interference problems on radios and GPS equipment.

    One of the best things you can do to prevent interference on a boat is to follow all the electronic equipment's installation instructions, and pay special attention to properly grounding all of your equipment so it can properly dissipate interfering signals/voltages to ground. Furthermore, I can't over emphasis reading your radar's owners manual and installation manual. It will certainly address some of the safety issues we are discussing.

    I hope this doesn't offend any of the other posters because a lot of what you said is accurate, but dpmimmack is not operating the same high power gear that some of you did while you were in the service. I was a tech for 26 years as I move up the ranks and worked on/around various radar & fire control systems till I retired in 2008.

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    Default radar placement

    Sounds like I should mount the radar on a hinged mast at the original height out of harms way.Thanks for the feedback

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    Member Maast's Avatar
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    Default

    The mast idea is a good one, I'd be interested in seeing a photo of your end results of mounting it like that.

    I'm sidestepping the whole problem and buying a BR24 radar, they only put out a tenth of a watt of power vs the usual recreational marine radars 2KW.

    Huntkodiak has a very good point in that the 5 MW 250 mile air surveillance radars I'm used to being around are a lot different than small boat radars.
    My feelings of radars being dangerous are probably exaggerated, but I still wouldnt get in front an operating radar though.

    One of the space tracking phased array radars I worked on would sometimes knock birds out of the sky within 100 yards of the array face.
    2696 Sea Raider Pilothouse
    "Dominion"

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