VHF Antennaes

[Jackman]

I think its time to replace my VHF antennaes. The radios have always worked fine but the antennaes are getting brittle and the cap is off of one so im assuming it has water in it and is not at its best.

Anyone have some advice on what to get? I have a flybridge and was thinking of at least getting an extension base for a good quality antennae to get it up over the hard top. Name brands and best choice as far as db rating would be helpful. I fish offshore mostly if that helps.

Thanks,

Jack

[bostonhatteras]

VHF antennas are rated in decibels and that is a measure of the angle the signal radiates out at. Sailboats, because they heel at deep angles have low decibel antennas thAt radiate in a 360 degree pattern. Powerboats typically use 8 or 12 decibel antennas that radiate out at around 45 degrees or 25 degrees respectively. The angle the signal is radiated is the strongest area of broadcast, it's not a perfectly exact thing. A higher decibel antenna will send its signal further because of the more acute angle it sends the signal within. However, no
VHF antenna will send over the horizon. It must be able to see the destination or receiving antenna. Single side band radios are used for far offshore where the horizon eliminates the ability of the two antennas to see one another.

[bostonhatteras]

Digital antenna has an edge over Shakespeare in my opinion but both are good. The name 'digital' is purely semantics, only marketing.

[bostonhatteras]

VHF antennas are rated in decibels and that is a measure of the angle the signal radiates out at. Sailboats, because they heel at deep angles have low decibel antennas thAt radiate in a 360 degree pattern. Powerboats typically use 6 or 10decibel antennas that radiate out at around 45 degrees or 25 degrees respectively. The angle the signal is radiated is the strongest area of broadcast, it's not a perfectly exact thing. A higher decibel antenna will send its signal further because of the more acute angle it sends the signal within. However, no
VHF antenna will send over the horizon. It must be able to see the destination or receiving antenna. Single side band radios are used for far offshore where the horizon eliminates the ability of the two antennas to see one another.

[bostonhatteras]

Please see my corrected db specs on repeated post. I couldnt figure out how to edit on the iPhone!

[Jackman]

I got smart after I posted and searched the site's previous discussions and found a very informative points. I think some of the same participants from a discussion of several years ago are still on the board today. Good stuff.

Anyhow. Is there anything gained by using a lower db antennae with a 10ft extension versus the large 16ft or so 8 and 10db antennaes? Figured I'd get a wider signal to go a bit further...but will it give me anything more than going with a higher db antennae that is already 16ft out of the box? What I want to avoid is loosing transmission in the rough stuff.

I guess with a higher db antennae the coast guard is more likely to hear me?

[Jackman]

I'm thinking 10ft extension with an 8ft 6 or 8db antennae might, in theory be the best config on my boat....correct me if I'm wrong. Im an offshore stype so I need some distance capabilities..I also have the issues with being in the rough stuff so going too tight of a trans/receiving angle might be a problem. Seems that 6 or 8db might be the optimum to avoid the rough seas issues associtated with vhf. So if I get 6 or 8db higher with a 10ft extension I may be better off than a 10db in rough seas...probably even in flat calm as well.

I dont see any notable difference between digital and shakespeare from my readings so far....saw an old article comparing several different types of antennae...was pretty much a wash as far as performance....digital seemed more rugged at the time but I think shakespeare made up for that to date.

I may replace one of the two antennae with a higher db at some point but I want the optimum antennae for my most used radio at the helm.

[Avenger]

Here's a formula for antenna height and range, from Shakespeare's site:

To determine the range of an antenna, multiply the square root of its height (In feet) above water by 1.42. This gives the range in miles.

Remember to perform the calculation for BOTH vessels, then add the results to get the range between two vessels.

IIRC the last time I was studying antennas adding 2 or 3 feet to the height produced no significant range improvement. In the end I was planning to keep it straightforward with an 8ft 6db antenna and an eight foot extension.

Naturally it's all what you're comfortable with, but IMHO the CG's antennas are tall enough to reach you, and boats that are outside of the range of your antenna are probably too far away to help anyway.

[jim rosenthal]

You are better off with an antenna that is designed as a taller one, rather than adding an extension to an eight-foot antenna. Digitals are very well-made; the Galaxy series from Shakespeare are also very well made. Regular Shakespeares are mediocre. Look at Shakespeare's 5399, I think it is called- the Galaxy version of something they used to make called a 399-1, which has always been a good performer and isn't outrageously expensive. And also look on line for prices, because better deals are out there.

[Boatnut]

QUOTE=jim rosenthal;214651]You are better off with an antenna that is designed as a taller one, rather than adding an extension to an eight-foot antenna. Digitals are very well-made; the Galaxy series from Shakespeare are also very well made. Regular Shakespeares are mediocre. Look at Shakespeare's 5399, I think it is called- the Galaxy version of something they used to make called a 399-1, which has always been a good performer and isn't outrageously expensive. And also look on line for prices, because better deals are out there.[/QUOTE]

This confuses me. I have always understood the length of the antenna is a function of the frequency. I understand there are antennas built a half and quarter waves and loaded antennas that allow for shorter physical measurements. As for how high to mount the antenna, the higher the antenna the further you can see on the horizon.

If you are going to be offshore 20 miles or more a lot, single sideband is the way to go for reliable communications. It's not uncommon the receive signals on VHF from farther than 25 miles away, but transmitting that far is a stretch.

Remembger the Coast Gaurd is using equipmet that is more sophisticated that anything the average boater is using. Don't make the mistake of thinking if you can hear them, they can hear you.