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.

 

[jim rosenthal]

You're right. I think, though, that you get more for your money if you buy (for example) a 14ft VHF antenna which was designed to be 14 ft long, rather than an (another example) an eight-foot antenna on a six or eight foot extension. I think the longer antenna will have more gain than a shorter one which is just put up higher. Your reception would be better with a short antenna if it was put up higher, but your transmitting capability would be better with a higher-gain antenna. I remember having this explained to me years ago by a marine electronics installer; since the technology hasn't changed a lot, I think this probably still holds.

I did not think to ask where the antenna is going; but on my boat, which has a fly bridge, I have a 5399 up on the bridge (that antenna is about eight or nine feet long) and a 14ft Galaxy, I can't remember which one, on deck which rises up past the bridge. The first one is connected to the bridge VHF; the second to the cabin VHF which is the backup. Both radios are connected by modular plugs so that if I would need to, I could move the downstairs radio to the bridge if the bridge radio stopped working. Not that it ever has, and it must be ten years old now.

 

[Jackman]

Just remembered I have a plce on my hardtop to mount antennaes...after Jims comment. I was planning on installing the extension mounted to the deck next to the flybridge and an 8ft antennae on top of the 10ft extension. Would it be best just to mount it to the hardtop? Is it stable swinging that high in the air? Right now my antennae are mounted halfway up the superstructure of the flybridge. They do not make it much higher than the hardtop....probably a good portion of my problem.

 

[jim rosenthal]

It depends where you do your boating and what you want. If you are going to put it onto the hardtop then it should not be any longer than eight feet. I think your maximum for a boat that size ought to be a 14ft antenna mounted on deck with a standoff to stabilize it, at least halfway up. There is a fourteen-foot Shakespeare that would probably do what you want just fine. I think that's what I have and it's worked admirably. Digital doesn't make a 14ft, I don't think- goes from eight to sixteen if I recall right.

 

[Boatnut]

I would think the best is to have the antenna above the hardtop. Whether you do it by mounting it on the top, or use an extension, one might consider which is easier to raise or lower if need be. The antenna length is a function of frequency, on SSB radios a antenna tuner is used for optimal performance. Such a tuner is not practical for a marine VHF radio. The rule of thumb for VHF, for what it's worth is approximately 25 miles, from there SSB is the way to go.

 

[Avenger]

My reasoning behind the 8ft antenna with an 8 ft extension was that my configuration has the extension mounted on the side of the flybridge with a standoff on the hardtop. This got the radiating part of the antenna a few feet above the hardtop.

I had originally purchased a high gain antenna that was something like 18 ft but discovered that the entire unit will radiate vs just the top portion. I realize that it's likely a non-issue, but I wasn't keen on the idea of having that right next to me. BTW, I discovered that whatever their other faults, West Marine has an excellent return policy.

It's certainly acceptable to mount the antenna directly to the hardtop, but in my case it made access for lowering the antennas difficult.

 

[Jackman]

Scrod,

That's what I was getting at...just did not get my explanation clear enough. I have a flybridge with an enclosed bridge/hardtop. I need to get the antennae higher so that the entire radiated part is above the hardtop. I was thinking if I mounted an eight foot on the mount installed a foot or so just below the top on the uprights to the hardtop I would get improvements in my transmission capabilities. Now 90% or so of my antennae is below the hardtop. Then I thought with the 8fter that high it might snap in rought seas.....so would it be more rugged if I used the extension mounted on the deck, then stayed off where the hardtop has a mount for the antennae on the upright and then add the 8ft antennae on top of that. She'd be up there compared to what I have now and I could probably transmit to Mars at that point!

So if I went with that setup what db would be best? I have not seen any 8ft antennaes over 6 db so 10db is not gonna happen...rather have the wide transmitting cone (whatever you called it)...what would be the most optimum db for antennae which has 8ft of irradiating capability above my hardtop and has a base starting 8-10ft off of my deck? Pretty high but not uncommon in my area.

 

[Avenger]

To clarify some things I'm reading here; An extension is just that, it doesn't become a part of the antenna, and thus doesn't do anything for gain, it just adds height. I haven't seen a regular 8ft antenna that has more than about 6dB of gain, but they may exist. The one I had was 9 or 10 dB but was an 18ft 2-piece and it just wasn't going to work on the boat. Most manufacturers specify that an extension be supported around 4 ft from their base. I wouldn't worry about breaking an 8ft antenna on a properly installed an 8 ft extension.

Radio is not my expertise, and there's people here with more technical experience. But my conclusion was that the 8 and 8 combo instead of a 2-piece high-gain worked the best for my application to get the transmitting antenna above the hardtop (and my head) and make it easy to raise and lower. In the end it's all a compromise and you have to make a decision that you're comfortable with. Hope this helps.

 

[Jackman]

Scrod,

My goal was to get the entire radiating portion of the antennae, or at least most of it above the hardtop. A 14 or 16ft antennae would probably be a waste since most of it would be transmitting/rx into the side of the superstructure of my boat. With your approach, the entire antennae would be above my hardtop so i
Id get 360 degree tx/rx capabilities.

Now...where is the best place to get all of this....looks like digital and shakespeare galaxy are nearly equivalent so thats a wash. I want all of the connections/cable already assembled so no soldering.

 

[Avenger]

I believe Digital has a small connector that comes pre-installed that lets you run the wire through smaller holes then you use an adapter to connect it to the radio. Not sure about Shakespeare because I was primarily looking at Digital.

I've had good luck buying from Hodges Marine http://www.hodgesmarine.com/ and they carry Digital and Shakespeare. Hope that helps.

 

[Artzco]

Jack, I just replaced my two antennas and extensions a few months ago with Galaxy series. Mine are mounted about half way up the side of the flybridge with a supporting mount near the hardtop roof line. With 8' ext and 8' antenna, I have about 12' above the roofline. I've been amazed at how great & clear the trans & receive has been since I put them in. As for the concern about connectors, the gold plated Shakespeare PL-259-CP-G work great and allow for a solid and solderless connection.

I ordered from Defender since they had the best price.