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I have an 8 ft antenna and it just broke off recently, nearly in half. I am buying a new one and wondering what the real world difference in range is between an 8ft and 4ft. If the 8 ft only gives you a small amount more and the 4 ft still gives adequate range, I would go with the shorter one.
Has anyone actually done tests. I just don't want that cumbersome 8 footer on there again unless its giving me a substantial amount more range.
Thanks
I was in the same situation with you a couple years ago. I honestly couldn't tell that much, if any, difference b.w the two. I went from an 8' Digital antenna to a 4' Shakespeare Galaxy that pretty much had the same specs aside from height. Aside from performance, the Digital was really whippy and the Galaxy is not which wasn't a big deal except when trailering and the antenna is in the down position. Every time I hit a bump in the road the Digital would hit my T-top frame and ended up leaving a nick in it.
There is a difference in performance between a 8ft and 4ft antenna whether or not it is important to you is another matter. If you do not go way off shore the 3db probably will be fine if mounted high and in the clear. The coast gaurd in Charleston uses the 4ft antennas on their RIBs. If it is good enough for the CG it is good enough for me. High and clear is very important with VHF so I have my 4ft whip mounted on the top of the bimini and it has never let me down.
the above said is true. Look at it like this, When fishing with another boat line of site you'll be just fine for miles. If you need CG help call on 16 they here everything including handhelds. Save the money and space.
It depends on where you will be. I have a 4' and got it for similar reasons - I didn't want to deal with the additional length antenna for the types of boating I was doing. Now that I am in the ocean a lot, however, I found out that I need the 8'.
The calculated difference in range for the two antennas is not much - 3/4 of a mile or so. Thus, in good conditions, the 4' will suffice. However, I have noticed in larger seas - 4 to 5 or 6', where you don't go deliberately but you can get caught in - a great deal of the antenna gets blocked by the waves, particularly when you are in the trough, and I couldn't even receive the weather stations. Thus, if you go into the ocean or large bays, I suggest you stick with the 8'. It also has more gain, which provides a better transmission pattern.
The range difference between an antenna 8 feet off the water and one 12 feet off the water to another antenna 8 feet off the water is one mile (calculated). On my offshore boats, I have two 8 foot antennas mounted 8 feet off the water--inshore boats a 4 foot antenna 4 feet off the water.
On VHF hight in might. The higher the antenna the better.
Therefore, no matter how you figure, the 8 foot antenna will be better than a 4 footer if mounted in the same location.
The question here is how long is your boat? What size antenna are you willing to put up with? How far offshore do you go?
The boat I just got has a three foot whip mounted on the grab rail around the center console. I want to replace it with an 8 foot whip mounted on the gunnel. I may get a t-top and if I do the antenna will go up there, and it will be an 8 foot whip.
If you want to calculate range, here is the formula.
Range in miles for the 6 db antenna (8 foot whip) = square root of height above water (in feet and measured to the tip of the antenna) x 1.42 = range in miles. This is an approximation, but fairly accurate. As you can see by the math, the higher the better. If your freeboard is three feet and the antenna is 8 feet, then the range is the square root of 11 (3.3166) x 1.42 = 4.7 miles. For a three foot antenna mounted in the same location (the gunnel) the range is 3.75 miles. Approximately. The reality is that the coefficient of the equation (1.42) changes depending on the gain. The higher the gain, the higher the coefficient. So the 4 foot antenna range may be overstated a tad. But you can get a general idea.
If you want your antenna to last longer, get a ratchet mount and lower it when trailering or passing under a low bridge.
__________________ 1999 20 foot Seagull power cat
Single 135 Optimax outboard
Location: Los Angeles, FL.or Georgia, depends. In Fl now.
Posts: 5,979
RE: 4ft vs. 8ft VHF antenna range??
Quote:
Sam Forbes - 5/26/2007 11:32 PM
I have an 8 ft antenna and it just broke off recently, nearly in half. I am buying a new one and wondering what the real world difference in range is between an 8ft and 4ft. If the 8 ft only gives you a small amount more and the 4 ft still gives adequate range, I would go with the shorter one.
The 4' survives low bridges. The 8' gets to be replace way moe often.
I've learned and have had a 4' now for mos. its mounted on top of bimini so it qualifies as a 12' antennae.
The gain does make a difference. A 6 DB with the same height to the tip of the antenna as a 3 DB antenna will get better range.
With my 8 foot antenna mounted on the gunnel I heard a Carnival cruise ship announce its intention to leave Port Everglades. I was by the Port Of Miami at the time. That was at least 20 - 30 nautical miles. Of course, the cruise ship antenna was probably a 9 DB (15 foot) antenna mounted at least 60 or 70 feet (or more) off the water. It was not the Imagination - it was the BIG Carnival ship.
From Miami I can hear Coast Guard station Key West if I drop the squelch on the radio. I tell people to go with the largest antenna they are comfortable installing on their boat, up to 8 feet (6 DB). Anything larger and you could have "picket fencing" problems on a small boat. And by small I mean less than 100 feet. Plus, who wants a 15 foot antenna on a 20 foot boat?? Talk about geeky.
__________________ 1999 20 foot Seagull power cat
Single 135 Optimax outboard
The range your radio will get is (your range) + (other station range). So if the math says your range is 5 miles, and the boat you are talking to has exactly the same antenna setup, then the effective range is 10 miles. If the station you are talking to is a shore station with a range of 30 miles then your range is 35 miles.
As you can see, the higher gain / higher antenna setup is most useful for ship to ship communications. So what antenna setup you go for depends on what and who you want to talk to. Other boats? Go with high gain antennas and mount them as high as possible. Shore stations? It matters less what you use.
__________________ 1999 20 foot Seagull power cat
Single 135 Optimax outboard
As others have said, height is very important with a line of sight device. Over the horizon is 12 miles.
Way offshore in large swells, many times I was hearing only 1 side of many conversations out there with my 8 foot on the hardtop. Broken transmissions when 2 boats are alternately dropping into a trough is not something we want out there as we could be asking for help. When I added a 4 foot extension to that antenna, it made a world of difference. For offshore, you need to get the antenna as high as possible.
Inshore in high traffic areas don't matter. A couple miles of range is all you need in sheltered waters.
Either way though, buy an antenna of good quality, avoid antennas with plastic ferrules.
If you are questioning whether you want an 8 or 4 foot antenna and you're worried about weight, you should probably go with the 4 foot antenna. The 8 foot antenna is much heavier and you don't get a "substantial" (subject to relativity) amount of more range.
Also: As Local Motion said - avoid antennas with plastic ferrules. 316 stainless steel for the win!
4ft vs. 8ft VHF antenna range?? 
