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VHF radio transmit distance

Old 10-02-2008, 08:12 PM
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Default VHF radio transmit distance

Is there a brand of VHF radio or type of VHF antenna that out performs others and gives greater send and receive performance over long distances?
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Old 10-02-2008, 09:38 PM
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Default Re: VHF radio transmit distance

Yes and no.

You can estimate the range of your VHF radio system with the following formula.

Range = square root of the height above water to the tip of the antenna times 1.42

Now this is just an estimate. And if you are talking to someone with an antenna the same height as your antenna then you can double that figure to calculate range.

This brings us to formula 2.

Range of station 1 + range of station 2 = range of the communication path.

Assuming that station 1 has a height to the tip of the antenna above water line on 15 feet, and station 2 has the same antenna height, applying this formulas we get:

(square root of 15 x 1.42) + (square root of 15 1.42)

Or:

4.62 + 4.62

Which is 9.23. So in this case you could expect 9.23 miles.

If you assume a boat with an antenna 15 feet above the water (to the tip of the antenna) talking to a shore station (USCG or commercial tow service) with an antenna up 300 feet you could expect:

(square root of 15 times 1.42) + (square root of 300 times 1,42)

OR

(square root of 21.3) plus (square root of 426)

OR

4.62 + 20.64

OR

25.26 nautical miles.

Or thereabout. Radio signals can propagate beyond this range.

One can clearly see by the formula that HEIGHT IS MIGHT! I would rather have 10 feet of antenna height over 10 more watts of power. 25 watts is more than you need for VHF use, and 25 watts is a fair power limit for VHF marine radios.

Greater gain antennas do not exactly increase range, it is still line of sight - they just help provide for a stronger signal when communicating with a station on the edge of reception.

Pretty much I do not believe that there is a radio out there that significantly outperforms another radio, nor do I think a 1/2 wave antenna made by company X outperforms a 1/2 wave antenna made by company Y.

Apples are apples after all.
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Old 10-03-2008, 07:23 AM
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Default RE: VHF radio transmit distance

Lazy_Iguana

Excellent and well explained post!
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Old 10-03-2008, 07:42 AM
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Default Re: VHF radio transmit distance

One thing I'll add. While on 1/2 wave shouldn't outperform another 1/2 wave, some antennas are simply made batter than others. Up here in the NW many of our offshore skippers are tossing their Shakespeare antennas and switching to Digital Antennas. With very few exceptions, Digital has flat outperformed Shakespeare. I don't work for either company, and earn nothing more than a hand shake from installing antennas so take it or leave it.

Digital Antenna
Comrod
Morad

Just depends on how much you want to spend.

Oh also the one thing you never want to hear from the USCG when you are calling for help, "Vessel hailing the USCG, please repeat your last!"
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Old 10-03-2008, 08:52 AM
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Default Re: VHF radio transmit distance

Marine VHF power output is limited to 25 watts by the FCC in the U.S. and by other National Authorities elsewhere. Claims of dramatic differences between manufacturers antennas are anecdotal only and have not been substantiated by independant objective tests, but believing something is better makes it better for the believer. There are occasional reports of atmospheric effects extending the range of a VHF; these are transient conditions. Several sections of the Standardized Code of Murphy's Laws (SCML) apply.
Does this mean you will always be able to reach the Coast Gurad 25 miles away? No. Does it mean you can't reach the Coast Guard 40 miles away? No.
If you have a DSC VHF, connected to a GPS, and you push the little red button, your MMSI and position will get thru to the Coast Guard in a 27 millisecond data burst, through a lot more interferance than a voice call, and the person pushing the button doesn't need to know your latitude and longitude. If there is a Class A DSC-equipped ship in the vicinity, it will relay your emergency call. NOW we're talking RANGE.
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Old 10-03-2008, 10:01 AM
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Default Re: VHF radio transmit distance

Yes, Lazy, great post. Only I could have done it better!!

sandyda,
"Claims of dramatic difference between manufacturers" HAS been tested, and HAS been proven with fact. I for one did a side by side test with a 8' Shakespeare and the 8' Digital Inc antenna's. The first thing you notice is, the Digital is heavier, and made better, more solid, especially in it's finish. After 8 years, my digital looks the smae as it did the day out of the box. After 8 years, a Shakey starts flaking those anoying fiberglass fibers that get caught in your skin.... Then there is performance, I could not test distance effectivley in my test, BUT, I could easily test the receive side. Sololey with my ears, I could tell a difference, the Digital picked up remote converstaions that the shakey did not. You had to listen very closely, but you could here a difference. The Digital is rated better, it's got a higher gain, and that explains that. I did not see any noticable difference on a VWR meter for both power output (they both showed 26.2 watts output: I was using an Icom radio at the time), and SWR's which were also equal.
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Old 10-03-2008, 10:04 AM
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Default Re: VHF radio transmit distance

It would be nice to hear of a quantitative comparison of antennas to help settle this issue. I had the opportunity to try a few different antennas on my boat and then drive off with a hand held to see how far we could communicate. All conditions being the same, I picked the antenna that allowed me to talk the furthest. While not scientific, it was the best I could do at the time. And as far as SWR meters, I found what I read on the meter wasn't being reflected in the antenna's actual performance. Ugh.


Just wish a boat mag would just compare all of them and provide a comparison report, almost like a consumer's report for marine equipment - unless there's already report out there somewhere. ???
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Old 10-03-2008, 10:42 AM
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Default Re: VHF radio transmit distance

I'll second the "Height is King" idea (pick whatever antenna you believe is best).
My antennas are up high on extenders and my range is amazing. I often speak to friends 50 miles away who think that I'm in their inlet.
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Old 10-03-2008, 10:47 AM
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Default Re: VHF radio transmit distance

I have two ICOM 504's on my Whaler one connected to an 8' Digital 529and the other to a 8' Shakespeare Galaxy 5225 XP. Both radios perform equally good fishing offshore 40 - 60 miles. I am able to communicate with the Coast Guard at Fort Maconfrom 40 miles using either radio. I do like the 529's factory installed Gold mini-UHF female with mini-UHF male to UHF male (PL259) adapter. I've installed many of these antennas on recreational boats without issue. My 2 cents.
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Old 10-03-2008, 11:08 AM
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Default Re: VHF radio transmit distance

Mr.Chummer - 10/3/2008 1:04 PM



It would be nice to hear of a quantitative comparison of antennas to help settle this issue. I had the opportunity to try a few different antennas on my boat and then drive off with a hand held to see how far we could communicate. All conditions being the same, I picked the antenna that allowed me to talk the furthest. While not scientific, it was the best I could do at the time. And as far as SWR meters, I found what I read on the meter wasn't being reflected in the antenna's actual performance. Ugh.


Just wish a boat mag would just compare all of them and provide a comparison report, almost like a consumer's report for marine equipment - unless there's already report out there somewhere. ???
An eight foot VHF antenna is little more than an eight foot conductor inside a fiberglass pole. While the argument can be made that one manufacturer builds a sturdier or longer lasting antenna than another manufacturer, or a more convenient connector, the performance of one eight foot antenna will be the same as the next. The average boater does not have the equipment or expertise to determine any difference in antenna performance.
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Old 10-03-2008, 01:21 PM
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Default Re: VHF radio transmit distance

Thanks for all the reply's, seems there is still a bit of debate on this subject.
From what I have read I am guessing that if I go with the best quality and longest antenna I can get that will give the best range to my radio.
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Old 10-03-2008, 08:30 PM
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Default Re: VHF radio transmit distance

Actually...............

There COULD be a difference in one 8 foot antenna and another.

If you remove that 8 foot fiberglass shell, you will NOT find an 8 foot radiating element. If you do, then it is not a marine VHF antenna - it is for some other crazy frequency band.

I do not understand how the marketing claims work on antennas. It seems that all 8 foot antennas claim 6db gain. But they are not all the same design. For example, I bought a West Marine brand antenna made by Shakespeare. The Mariner 8500 or something.

And I broke it. But I thought the shell would be useful for something (broke the antenna at the base) so I decided to keep it. I pulled the guts out and discovered a 1/2 wave or 5/8 wave end fed antenna. I did measure the element, but I forgot what it was. I am pretty sure that what I found was a 1/2 wave antenna however.

At 156.800 mhz, a 1/2 wave antenna is about 3 feet long. This means that 5 feet of that "8 foot antenna" is empty space. Actually it is feed line, the actual antenna was hanging by a string attached to the end cap. The tip of the antenna is about 8 feet from the base of the antenna, but the actual antenna element was only 3 feet long.

I just checked the WM website and they report that the Mariner 8500 is a 1/2 wave antenna. So now I am positive I am remembering correctly.

And this is where it gets confusing. At least to me.

The WM Mariner 8700 has a 5/8 wave antenna (about 9 inches longer than the 1/2 wave).

BOTH ANTENNAS claim a gain of 6db. The 5/8 wave should have some gain over a 1/2 wave.

But it gets better! There are other antenna designs used. There are collinear designs that in effect "stack" two 1/2 wave or 5/8 wave antennas - obtaining even more gain in the process.

Yet all 8 foot marine antennas are advertised as 6db.

Interestingly enough, the antennas advertised as "3db" are in effect 1/2 wave antennas.

This is where I think the "difference" from one brand to the next comes into play. Digital will take a collinear antenna and put it against a Shakespeare 1/2 wave - then claim a boost in range / performance. Well yea, you are not comparing the same two antennas here. You are putting a stacked 5/8 wave up against a 1/2 wave.

But put a 1/2 wave against a 1/2 wave, or a collinear 5/8 against a collinear 5/8, and that difference will vanish.

Anyhow - my Mariner 8500 works fine. I can hear cruise ships announcing they are leaving Port Everglades when I am at the Port Of Miami. I also find myself having to turn up the squelch, so that the weak signals from fairly distant stations are tuned out. It works just fine. I have no plans to "upgrade".
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Old 10-03-2008, 09:23 PM
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Default Re: VHF radio transmit distance

Birdman - 10/3/2008 1:01 PM

Yes, Lazy, great post. Only I could have done it better!!

sandyda,
"Claims of dramatic difference between manufacturers" HAS been tested, and HAS been proven with fact. I for one did a side by side test with a 8' Shakespeare and the 8' Digital Inc antenna's. The first thing you notice is, the Digital is heavier, and made better, more solid, especially in it's finish. After 8 years, my digital looks the smae as it did the day out of the box. After 8 years, a Shakey starts flaking those anoying fiberglass fibers that get caught in your skin.... Then there is performance, I could not test distance effectivley in my test, BUT, I could easily test the receive side. Sololey with my ears, I could tell a difference, the Digital picked up remote converstaions that the shakey did not. You had to listen very closely, but you could here a difference. The Digital is rated better, it's got a higher gain, and that explains that. I did not see any noticable difference on a VWR meter for both power output (they both showed 26.2 watts output: I was using an Icom radio at the time), and SWR's which were also equal.
I'll take issue with this. If you are buying an antenna today you are not buying an 8 year old antenna. I rigged my boat in 2002 with Digital 8' VHF and 8' AM/FM antennas. Worked great - no problems. In 2006 I had to rerig my T-top - as I was doing it I decided to replace the AM/FM antenna with a backup VHF antenna so I added a new Digital 8' VHF antenna (same model - 529-VW). After I rigged everything I pulled out of my driveway with the antennas halfway up. They hit the overhead cable - the original antenna was fine - the new one snapped at the base. Looking at the damage the fiberglass seemed very thin - I called Digital customer service and told them I would like to bring it in to the to have them determine if it was a defect or not. The customer service person I spoke to was adamant that if it hit something it was not warranteed and would not be covered. I argued that the other antenna hit just as hard and did not fail. Eventually he agreed that if I sent the antenna in they would look at it - I said as I lived less than 10 miles from their service center I would carry it in - he said no - it had to be mailed In the end I said screw it - bought a new (same model) antenna and installed it - I repaired the damaged antenna and gave it to a friend.

So last week I go out on the boat and raise the antennas. The same antenna has a 6" longitudinal split in it and is loose in the ferrule. It has never hit anything and has no visible damage anywhere else. I'll be calling Digital about it but given my previous experience with their customer service I am not expecting much. Getting it replaced doesn't give me a great deal of help as it will be at least 4 hours of my time to rerig it.

Moral of the story is that you cannot compare an 8-year old product to one you purchase today. My original Digital antenna does look good (not as good as new but it is in good shape) but I cannot buy the same antenna today.

Ed
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Old 10-04-2008, 04:53 AM
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Default Re: VHF radio transmit distance

VHF range is "line of sight" or basically distance to the horizon. The higher the antenna is elevated the the better the range. When cell phones (uhf I suppose) first came out there were so few towers you could not communicate from Bainbridge to Tallahassee while standing on terra firma. You COULD climb half way up a ten foot ladder and talk to someone in Tallahassee with clarity. I witnessed it many times.

The greatest breakthrough will be if satellite phones can be bought and used as cheaply as a standard cell-phone one day. I have serious doubts that will happen.

The previous reports are very professional and written with much more expertise than this one!
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Old 10-04-2008, 09:14 AM
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Default Re: VHF radio transmit distance

Birdman - 10/3/2008 10:01 AM

Yes, Lazy, great post. Only I could have done it better!!

sandyda,
"Claims of dramatic difference between manufacturers" HAS been tested, and HAS been proven with fact. I for one did a side by side test with a 8' Shakespeare and the 8' Digital Inc antenna's. The first thing you notice is, the Digital is heavier, and made better, more solid, especially in it's finish. After 8 years, my digital looks the smae as it did the day out of the box. After 8 years, a Shakey starts flaking those anoying fiberglass fibers that get caught in your skin.... Then there is performance, I could not test distance effectivley in my test, BUT, I could easily test the receive side. Sololey with my ears, I could tell a difference, the Digital picked up remote converstaions that the shakey did not. You had to listen very closely, but you could here a difference. The Digital is rated better, it's got a higher gain, and that explains that. I did not see any noticable difference on a VWR meter for both power output (they both showed 26.2 watts output: I was using an Icom radio at the time), and SWR's which were also equal.





If you are going to use your ears to determine the difference in the receiver I would recommend
using a sinader which you can connect to the speaker and read the signal to noise ratio. This
would be a little more scientific.

To the OP,
Height is king when you want distance, most of the new radios and the antennas yield similar
results if comparing apples to apples. You should make sure the selection and design of the
antenna will work on your boat. Make sure your antenna coax is properly terminated and
have it tested with a watt meter.



Steve
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Old 10-04-2008, 02:50 PM
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Default Re: VHF radio transmit distance

Lazy_Iguana - 10/3/2008 5:30 PM

Anyhow - my Mariner 8500 works fine. I can hear cruise ships announcing they are leaving Port Everglades when I am at the Port Of Miami. I also find myself having to turn up the squelch, so that the weak signals from fairly distant stations are tuned out. It works just fine. I have no plans to "upgrade".
Part of that as I have researched it is because that Mariner 8500 is a good antenna. It is a Shakespere Galaxy 5225 rebadged for West Marine to sell. So yes that is up there with the Digitals. We have a radio specialist guy up here in the Northwest. I had bought a cheaper antenna and was having fits with it. He was the one that showed me that series of antennas. He only recommends the Mariner 8500, Galaxy 5225 and Digital Antennas. He does not sell stuff either. Just does repair and SWR testing. He also re-soldered my connections with new ends for me. Not all solder jobs are equal either.

Another thing I learned about antennas while going through fits with mine is it is not all about the antenna. The co-ax cable and end connectors are very important also. Higher grade co-ax and then getting a real quality connector and soldered correctly is very important.
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Old 10-04-2008, 05:49 PM
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Default Re: VHF radio transmit distance

My Ex was convinced that a four hundred dollar dress was twice as good as a two hundred dollar dress. [can you see where this is going?] I took her to a Dress Factory in Dallas run by a friend of the family, and showed her that both dresses were made on the same line by the same seamstresses using the same materials. The difference was in the patterns and colors of the fabrics (less than 10% difference in cost) and the labels, of course. She didn't get it (I didn't either, come to think of it) and that was the beginning of the end.
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Old 10-04-2008, 05:54 PM
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Default Re: VHF radio transmit distance

Erp. I may have to eat my words. Here is a VHF antenna test from Practical Sailor Magazine:
http://www.practical-sailor.com/issu...es/5409-1.html
I'll have to go dig out the pile in the basement.
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Old 10-04-2008, 06:01 PM
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Default RE: VHF radio transmit distance

i have a shakespeare 5225flt and an icom m502 (both 2002 models). antenna mounted on a hardtop 9 feet off the water with no extender. i clearly pick up CG chatter from stations atlantic city and delaware bay. i'm out of sandy hook, nj. for the tech guys, out of curiosity, would my 25 watts make it back to them that far away? ron
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Old 10-04-2008, 08:15 PM
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Default Re: VHF radio transmit distance

I would agree strongly with what tcullin said.
I switched both antenna on my boat from Shakespeare Galaxies to the Digital brand..
Don't get me wrong... Shakespeare makes a good antenna... but the Digital antenna far exceeded the performance that I'd had with the Galaxy.
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