Garmin Fantom Radar: dome vs open array?

[Nick14]

I'm planning on a Garmin electronics package for my upcoming boat, which will include Fantom radar.

I would appreciate anyone's experiences or observations on a 24" dome vs. a 4 ft open array, in the Fantom.

Cruising waters will be coastal New England and Long Island Sound, from New York through Maine (frequent fog to be expected).

I'm not concerned with 'range,' the 48 miles of the dome is enough (vs. the stated 72 miles for the open array). I'm most interested in minimizing noise and ghost images, resolution, and being able to reliably punch through fog.

Any experiences would be appreciated.

Thank you!

 

[O C Diver]

Garmin use to have a very good tutorial on the difference (aside from KW power) in antennas.

In a nut shell, going to a larger wing offers several advantages. Probably the most important is target separation. Is that the lighted seabouy, the seabouy with a 25' center console next to it, or bouy and several boats. I have a 6' wing (which is overkill) but has great target separation. The difference between a small diameter dome and a 4' wing is substantial.

The other thing you want to compare between models is vertical beam angle. Ideally you want the transmission to be parallel to the water. A wider vertical beam angle can mean you will see objects closer to the boat. Essentially, as you approach an unlighted bouy on the edge of the channel, how close can you get to it before it disappears from the radar.

Ted

 

[OldDan1943]

JUST MY OPINION
Look up and understand “wink distance”. That is about the range of a RADAR.
The higher you mount the antenna, the greater the effective distance of your RADAR.
You will never be able to see further than the curvature of the globe.
Some say you will be able to see the weather beyond the curvature, I’m not sure that is true.
You can adjust the beam up and down so maybe you can pick up unlighted buoys but nothing replaces good eyes and paper chart. The paper chart tells you will the buoys should be located.

A 4ft array is about 42 miles. I agree with the increased sensitivity and maybe target separation of the larger antenna.

 

[twistedtree]

I have no experience with the Fantom products so can't comment specifically about them, but I can comment in general about smaller vs larger radar antennas.


First, I agree that the extra distance isn't very important. As has been noted, the height of your antenna vs the curvature of the earth will limit the radar's sight line well before power output will limit it.


As for the larger antenna, it affects two things that I think will matter.


The first is that the larger antenna concentrates the radar output into a narrower beam, and as a result places more power on a target, which means more power returned to the radar and better target detection. As a result you will pick up smaller targets sooner with a bigger antenna. Fisherman like this because it helps them spot birds, and where there are birds there are fish. The same would be true for picking up small boats that are loafing about. You will see them a bit sooner with a larger antenna. Note that this is related to the range spec for the antenna because it's the same concentration of the beam energy that increases detection range. So really the rage spec does matter, but not in the way it might seem.


The second thing is that a larger antenna smears targets less. Because the beam has a certain width, as it passes over a target is creates a return for the whole time the target is in the beam. This results in a smear of a target. The further away the target the bigger the smear, and as it gets closer the smaller the smear. In some cases, as you get closer you will see that the smear actually splits into two smears and that there are actually two targets close together, not one. The larger the antenna, the narrower the beam, which means smaller smears, and multiple target will become evident from a greater distance.


So all else being equal, the bigger the antenna the better. But space, cost, and appearance are all factors too. For casual navigation, a dome works just fine, is inexpensive, and the easiest to locate on the boat. But bigger antennas are better - it's just a question of whether it matters to you.