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Go Back   SailNet Community > General Interest Forums > Gear & Maintenance
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  #1  
Old 11-14-2007
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Radar antenna mounting

Need your help in selecting and installing pole for my radar antenna .
What I have seen commercialy available is upwards of $1K.
I thought of having one manufactured locally, some quoted prices ranged from $200 to $500, with 8ft 21/2 or 3'' aluminum. This would be secured to the transom with support to rails and one from pole to transom. The pole would have a base to secure antenna.
1. do I need to reenforce the transom area where it mounts to
2. material and size of tube adequate.
My assumption is that I need an 8ft pole with a flat plate on top and flange on bottom. Secure to transom leveled (squared) and add support rail and transom.
Or am I missing something?

Thank you
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Old 11-14-2007
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Well, that's 1 of 3,972 best & right ways to do it ....

I'm sure you will get plenty of suggestions.

I had a similar question; but about how important it is to have a radar gimbled to keep it level when heeling.

I'm interested to see what your cast line brings in....

Fred

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Old 11-14-2007
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Just remember this... RADAR uses microwaves. Microwaves cook meat. People are made of meat. With a 15 degree spread, anybody on the foredeck when it is on will be bombarded with those microwaves. And the word has it that gimballing is quite inportant. If you are heeled quite a bit, you will be looking at the sky and the water, not at the ships.

Personally, I'm looking at getting AIS over RADAR. I'm more worried about ships than anything else!
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Old 11-14-2007
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Quote:
Originally Posted by MiVelero View Post
1. do I need to reenforce the transom area where it mounts to
2. material and size of tube adequate.
My assumption is that I need an 8ft pole with a flat plate on top and flange on bottom. Secure to transom leveled (squared) and add support rail and transom.
1. Yes the mounting points will need reinforcing. 2. It sounds a little on the thin side to me.
A radar really needs to be high up to see far, so I view a mast mounting as being more efficatious.
You don't see many sailing boats with gimballed radar mounts, it helps of course, but mostly when you are healed over at 30 degrees or more, you are not watching your radar. Mostly you watch your radar in darkness and poor visibility when in the presence of danger. So your boat is likely to be moving slowly, upright and possibly under power.
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Old 11-14-2007
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I would agree that putting the radome up higher, where it is not going to present a danger to crew working on the deck makes a lot more sense. Having it on an eight foot pole in the cockpit, often means that someone standing at the mast or on the foredeck will be in the beam of the radar emitter... not exactly a good thing for them IMHO.

The Amana RadarRange microwave oven is called a RadarRange for a reason. Even the smaller units used on recreational sailboats are two-to-four kilowatts of power... and best avoided if possible.

I would recommend going with a mast mounted radome. Not only will it be safer, but it will give you a bit more range.
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Old 11-14-2007
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While mounting the radome on the mast higher up does indeed extend range and get the unit out of way of causing harm, I always worry some about the abuse the unit takes during tacks. Some go to elaborate (read "heavy") guards for this reason.

I chose to mount the radar on a stern post, high enough to avoid cockpit crew. Actually the main reason was that the cable supplied meant that a mast mounted radar required the display to be mounted below at the nav station, IMO not where it's needed most. Stern mounting allowed me to set the display up at the helm where it's most convenient when needed.

I didn't gimbal it on the premise that most of the time I'm concerned I'd be motoring slowly and more or less upright. In our regular cruising grounds wind and fog don't often coexist.
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No doubt the mast would be the best place the higher the better. But in all practicality to install the antenna on the mast I would have to step my mast
For the small amount gain in range vs the cost for longer cable and steping mast it is hardly worth it.
As for safety lets realize the time of exposure and distance to antnna is very minimum. Besides a bit of glow at night is not so bad.
I'm sure there are many of you with a transom mount antenna, what say you?
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Old 11-14-2007
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Marine radars work by transmitting brief pulses of high-frequency radio waves that are reflected by objects at a distance. The time taken for the pulse to go out and the echo to return is a measure of the distance to the target. The antenna revolves, sending out a searchlight-like beam. The beam has a narrow horizontal spread, in order to be able to distinguish between targets close to one another. It has a broader vertical spread to be able to compensate for rolling and pitching of the boat. The larger the antenna, the narrower the beam.

Radar transmissions travel in a straight line and only bend slightly over the horizon. The visibility of a target is determined by the height of the transmitter and the height of the target above water level. For a radar antenna mounted 25 ft above the water, the horizon is 6.15 nm away. If the superstructure of a ship sticks up above the horizon, the radar will be able to see it further away.

Radar antenna should be mounted where they have a clear all-round view, unobstructed by boat superstructure. Mounting too low will reduce the distance to the radar horizon. Mounting too high may reduce the radar's ability to see close targets. Never mount the antenna in a position where the heads (and eyes) of crew members will be regularly in the line of the radar beam.

Marine radar systems operate in the high radio frequency and microwave range. Unlike X-rays and nuclear radiation the emissions are non-ionising radiation and do not penetrate the human body but can cause heating of the surface, particularly of the skin and eyes (cornea). Measurements taken, in a port, 10 meters from the stationary scanner of a container ship fitted with both a 50 kW set and a 60 kW set, and tests carried out by a manufacturer of radar equipment 10 metres from a 10 kW set with a stationary scanner, have all shown power densities significantly less than danger levels. The examples show that the expected power densities from exposure to ships' radar at a distance of 10 metres are less than 1/100th of the investigation levels even when the scanner is stationary. Marine radars normally operate with a pulsed signal and a rotating scanner, so people are not continuously exposed to radiation even if they are in a fixed position. No link between ill health and exposure to microwaves at levels below the recommendations has been established among microwave communications and radar engineers in the armed services, electronics, broadcasting or communications industries.
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Excellent reply, Simon...
Should be remembered that the average power of even 'high powered (4KW)' radars are on the order of 4-5 watts, not even as much as your VHF. Not to imply that there is no danger however, as has been stated, especially to the eyes and gonads.
The video presentation is always noticeably better when the antenna is about the height of the 1st spreader or more...30 ft??
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Old 11-15-2007
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Quote:
Originally Posted by MiVelero View Post
No doubt the mast would be the best place the higher the better. But in all practicality to install the antenna on the mast I would have to step my mast
That's not a big deal and the mounting bracket will be less expensive than a transom pole.
Quote:
Originally Posted by MiVelero View Post
For the small amount gain in range vs the cost for longer cable and steping mast it is hardly worth it.
I think the gain in range is more than just a little.

But if you are set on transom mounting, why not go for an arch, where you can add all sorts of extra antennas, davits, solar panels, BBQs, etc..
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