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Antenna Recommendations For Small Center Console Boat
|Author||Topic: Antenna Recommendations For Small Center Console Boat|
posted 12-27-2008 11:30 AM ET (US)
I don't plan on going more than eight miles offshore in my [small center console boat, a 2004 Boston Whaler 170 MONTAUK]. What length antenna would be a good fit? I have seen a few pictures of [Boston Whaler MONTAUK boats] on this site that had [their VHF Marine Band radio antenna] bent down in front of the cooler seat. For that setup what length antenna it used? What range will you get with the VHF radio?
posted 12-27-2008 12:00 PM ET (US)
I have a 19 Outrage II but I have mine set up with an adjustable mount like this bolted to my console with a wood backing plate.
I really like the extra length even if only going out 8 miles. I find myself chasing fish and going further and further. If you need help there is no such thing as too big an antenna.
|Casco Bay Outrage||
posted 12-27-2008 02:25 PM ET (US)
A GAM 3' whip on a Shakespeare 4' extension will work as will a 8' Shakespeare.
As you know the length and height of the antenna is the key to good reception
Here is a good reference article by Jim:
I have an 8' on a ratchet rail mount on the stern rail of my 1991 Outrage 17.
In this photo, you can see my setup (on the left) next to Seth's 170 mounted on his console, followed by Randall's Revenge 19.
Here is Seth's photo album on his setup:
The thread that led to his install is here:
posted 12-28-2008 11:47 AM ET (US)
The range of a VHF radio transmission from a boat is more affected by the height of the antenna above the water than by the length of the antenna.
posted 12-28-2008 06:53 PM ET (US)
[G]ood information, but [I] guess [I] will just go to [W]est [M]arine. [M]aybe they will have a good setup for my boat[.]
posted 12-29-2008 08:08 AM ET (US)
Let us know what your local West Marine comes up with. My West Marine is walking distance to my home so I do go in there from time to time. I seldom find they are as knowledgeable to the specific needs of your Boston Whaler than the fine people on this web site. I bought the stainless steel antenna mount and other mounting odds and ends at West Marine, however the research and advice to get to that point was all found on ContinuousWave.com
posted 12-30-2008 12:27 AM ET (US)
froberts--A 3-dB [gain] antenna will give a good signal about 4 to 6 miles on the average while a 8-db antenna will give up to 15 to 18 miles and more. I transmit all the time at 12 miles to the ranger station. Most all of the [6-dB gain antennas] are 8-feet long. Height is important for sure but the 6-dB [gain] rating gives you a stronger signal and greater range. West Marine's catalog has a excellent article on the subject. high sierra
posted 12-30-2008 11:35 AM ET (US)
For a technically strong article on the range of communication and how height above terrain has more influence than antenna gain, please read my article in the REFERENCE section:
Marine VHF Radio Communications
I would always prefer to have an antenna with half the gain mounted twice as high than to have an antenna with twice the gain mounted half as high if the goal were to increase the range of ground wave communication.
The problem in high sierra's range estimates is the completely erroneous assumption that the length of the fiberglass casing of a VHF Marine Band radio antenna is automatically proportional to the length of actual radiator of the antenna. Most of the lower priced antennas constructed in an 8-foot fiberglass tube only have an actual antenna length of 36-inches or so. They are simply "three foot" antennas constructed in an eight-foot tube.
In general the gain measurements used by manufacturers to sell antennas to boaters are unrepresentative. Proper gain measurements are made in reference to a half-wave dipole in the same environment. Marine antenna gain is usually given in reference to a isotropic radiator in free space. Stating gain in that fashion gives all antennas a boost in gain.
But when in doubt, just follow the advice of the WEST Marine salesman.
posted 12-30-2008 01:17 PM ET (US)
[I] have four [W]est [M]arine [stores] in my area and did not find any one with real knowledge on antenna. They made a lot of guesses but no hard information--"just try and see maybe this one will work." Spending my money has never been so difficult. I guess [I] will try [B]oater['s] [W]orld this time around
posted 12-30-2008 03:13 PM ET (US)
It is not so much the length of the antenna as [its gain]. See West Marine's well written article in their catalog. I just switched to a 6-dB [antenna] from a -3dB [antenna] and the range is greatly increased. I could hold up my 3-foot 3-dB [anetenna] over my head and noted no better signal to the ranger station. With a 6-dB [gain antenna] the signal is squeezed into a flatter signal that has greater range. This is a well known fact. A 9-dB signal on a rolling boat has poor reception as the really narrow band is not getting to the receiver except as a make and break signal. Read the article. high sierra
|Casco Bay Outrage||
posted 12-30-2008 03:22 PM ET (US)
After reading several threads and Jim's article, I think you will know more than most sales people.
I went to a reputable store and got nowhere. After doing some searches and reading here, I learned the answers to my questions, saw photos of various setups and got honest reviews of products.
I see several good threads by entering "antenna+install+170" in the site search page. Here is a link to the results:
Deciding the type and location of an antenna is not a simple thing.
Good luck at Boater's.
P.S. Jim H - That link is awful!
posted 12-30-2008 03:44 PM ET (US)
thanks for the info i think i am going to use the 4 foot digital antenna 528-vw and mount it to the top of the console rail with a dm 178 rail mount
posted 12-30-2008 11:27 PM ET (US)
high sierra--You are welcome to maintain whatever belief system you like in regard to marine radio antennas.
No matter what the West Marine salesman says, as soon as a radio wave is emitted from your antenna, it obeys the Laws of Physics. The wave can't tell what brand or type of antenna is has been emitted from. The wave travels in a straight line and has the same range to the radio horizon as all other radio waves. The best way to increase range is to increase height.
In regard to antenna gain, that is something that is easy to sell but hard to buy.
It has been anecdotally observed many times that the often cited comparisons of new antennas to old usually involved a comparison of a working antenna to a broken antenna, and in this way many spectacular but undeserved accolades have been earned by particular brands or varieties.
posted 12-31-2008 06:42 PM ET (US)
Jimh, you are entitled to your ideas as well as I am. The main purpose of a VHF antenna it to provide a radiator for the power that the transmitter produces and to radiate this energy in the correct direction. An antenna's db (or antenna gain indicates the apparent increase in transmitting power due to its ability to focus energy. Antennas with a db rating concentrate energy perpendicular to the antenna shaft in a field that is shaped like a disc. This makes your radio signal appear stronger to receiving stations around you. It also reduces the amount of energy that is transmitted above and below the antenna. As the db rating of the antenna increases, so does the height of the antenna( as marketed normally), but the horizontal angle diminishes. A gain increase of 3 db means a doubling of signal strength. A 6db is a fourfold increase and a 9 db in an eightfold increase.The actual watts transmitted doesn't increase, it's just that the power is concentrated. Therefore a radio with a 6 db antenna will sound like it has a larger transmitter than the same radio with a 3 db antenna. The receiving station will receive you much better with a stronger signal from a longer distance with a 6db antenna. . high sierra
posted 01-01-2009 12:43 AM ET (US)
The radio horizon is the primary determinant of range in ground wave communication between VHF stations, and the radio horizon is determined by the antenna height.
With 25-watt transmitters and receivers with quarter-microvolt sensitivity, there is very ample reserve gain in most practical paths, and a difference of 3-dB will generally not even be noticeable. It will only come into play when the path becomes very marginal. The fade margin on a ten-mile path is something like 50-dB, so the path has to severely degrade before the extra 3-dB makes a difference.
All antenna gain comes from narrowing the radiation pattern. On a small boat the stability is not great so an antenna is typically in a lot of motion. The narrow pattern of a gain antenna becomes a liability instead of an asset.
Generally when beginning from the low mounting height typical on a boat, if you increase the antenna height you will extend your range farther than if you use a higher gain antenna at the lower height. This is especially true when the lower portion of the high-gain antenna is mounted practically on the deck. The lower portion of a high-gain antenna is not effective when it transmits into the console, the people, the rigging, and other things around it.
In the United States the FCC allows FM broadcast stations to choose between height and transmitter power as options for creating their coverage area. I don't think you can find one example of a broadcast station which would give up antenna height in favor of higher power. Everyone wants the highest antenna site they can get.
Another problem with VHF Marine Band antennas is that often the gain is just a number printed on the side of the shipping container. When you buy gain in the antenna, there is not much guarantee of delivery. This is especially true in the case of the less expensive antennas. That "6-dB" gain is often just not going to be obtained. In contrast, adding height always delivers improved range.
posted 01-01-2009 02:03 AM ET (US)
Jimh, have a great new year . The best to you and yours. high sierra
posted 01-02-2009 09:16 AM ET (US)
Further to my comments about the importance of height in determining the range of communications, I quote from a very technical paper on the topic of non-line-of-sight (LOS) path loss, as follows:
General Non-LOS Propagation Models
"There are many more general models and empirical techniques for predicting non-LOS path losses, but the details are beyond the scope of this paper....One crude, but useful, approximation will be mentioned here: the loss on many non-LOS paths ...can be modeled quite well by a fourth-power distance law."
In other words, the rate of signal decline with distance on a LOS path is normally proportional to the distance squared. Once you go beyond the radio horizon and the path becomes an over-the-horizon or non-line-of-sight path, the rate of signal decline become proportional to the distance to the forth power.
"Antenna height becomes a critical factor, and getting your antennas up... will often spell the difference between success and failure."
In this same paper the following recommendations are given in this order:
"--Always strive for LOS conditions"
"--Use as much antenna gain as is practical."
There is no argument made here that antenna gain is not useful. Indeed, antenna gain is extremely useful since it contributes to both improved transmit and improved reception. The point that I have been making is that antenna height is fundamentally more important than antenna gain in the situation we typically find in a small recreational boat. Due to the practicalities of installation on a small recreational boat, antenna height is hard to come by. Raising an antenna four feet may represent an almost doubling of its height. This can make a dramatic increase in communication range.
In other circumstances, an increase in antenna height by four feet would not be of much significance, and higher antenna gain may be preferred. For example, if our antenna were already 25-feet high, raising it four more feet will not produce a significant gain. In that situation it is more effective to increase antenna gain. But when an antenna is installed at very low height above the water, as typically occurs on small boats, adding four feet can improve the LOS path range.
posted 01-02-2009 11:44 AM ET (US)
Using an 8 foot antenna vs a 4 foot antenna may make the difference in the Coast Guard hearing a clear distress call over a garbled and broken call. Most distress calls happen in rough conditions where the antenna is affected more by swell height. Most distress calls are made in a panic tone and speech is usually frantic because you are not calm. You may only have the ability to transmit a single distress call. Say your boat is on fire 8 miles out in 4 foot close chop. One panic call with just enough time to give your lat-long position and you have to go over the side. Go for the larger antenna. It won't look as pretty as the 4 footer but the 8 footer takes up no more space, other than when stored.
posted 01-02-2009 05:49 PM ET (US)
Sorry--but again I disagree.
The antenna length makes no difference on the modulation, so you can throw out all the comments regarding yelling into the microphone, garbled speech, and so on.
In a rough sea state a higher gain antenna will experience a greater influence on its radiation pattern with movement. The only way an antenna has gain is if its radiation pattern is more concentrated. In rough seas a higher gain antenna will be pointing its main lobe all over the place.
There is no telling what is inside an "8 foot antenna." There might only be a 3-foot radiator in there.
On a small recreational boat install your antenna as high as possible.
It is always possible to demonstrate some situation in which 3-dB more antenna gain will help, but it is equally possible to demonstration how higher antenna mounting will help as much or more.
posted 01-02-2009 06:49 PM ET (US)
If there is only 3 foot radiator in there, would it not be in the top of the antenna?
posted 01-02-2009 11:32 PM ET (US)
If an 8-foot long antenna contains only a 3-foot radiator, it would be completely reasonable to expect that it would be located as near to the top of the antenna as possible. It would also be completely reasonable to expect that such an 8-foot antenna would have no more gain than a three-foot antenna. Actually, such an antenna would be a good choice, as it would help to raise the height of the antenna.
When considering the height of an antenna the usual notion is that one measures to the point of the antenna which has the maximum antenna current. In an antenna whose radiator is only 36-inches there will only be one maximum current point. Longer antennas which have radiators that consist of stacked sections usually have two points of maximum current. In such an antenna the height would be most appropriately measured to a point equidistant between the two current maxima.
posted 01-03-2009 02:21 PM ET (US)
In describing the difference in communication results between antennas of 3-dB gain and those of 6-dB gain, it was mentioned above that:
"A 3-dB [gain] antenna will give a good signal about 4 to 6 miles on the average while a 8-db antenna will give up to 15 to 18 miles and more."
This is, unfortunately, pure nonsense. To suggest that an increase in antenna gain of 3-dB will provide a treble increase in range is completely unsupported by the underlying Physics of a radio transmission circuit.
In a typical communication circuit between two vessels or between a shore station and a vessel at a range of 4 to 6 miles, in which both stations use 25-watt transmitters and receivers of the typical sensitivity, I have already shown that there is a fade margin of over 50-dB in the circuit. (See http://continuouswave.com/whaler/reference/VHF.html .)
In order for a 3-dB difference in antenna gain to have any influence, the path loss between stations would have to be reduced to the point where a change in strength of 3-dB could have an impact. In the path described above, there is a reserve of over 50-dB in signal strength which would have to be lost before a 3-dB change in antenna gain could be noticed. The only basis on which a 3-dB increase in antenna gain would be likely to be significant is when the fade margin degrades to 3-dB or less.
posted 01-03-2009 06:53 PM ET (US)
You guys no better than mentioning the word "antenna" around our beloved leader Jim! Just once,a short simple easy to understand answer would be wonderful Jim. The mass amount of technical jargon you are capable of is lost to most lay people like me. We all appreciate you Jim and thanks for our site. Happy belated New Year.
posted 01-04-2009 10:55 AM ET (US)
I cannot provide more concise answers than I have already. Quoting myself:
"The range of a VHF radio transmission from a boat is more affected by the height of the antenna above the water than by the length of the antenna."
"On a small recreational boat install your antenna as high as possible."
As for specific recommendations, I have already given that advice in an article published some time ago. Please see:
VHF Marine Band Antennas For Small Boats
This article was mentioned by another participant in the discussion in the early replies.
posted 01-12-2009 04:21 PM ET (US)
I copied jimh and I now have a GAM 3' whip on a Shakespeare 4' extension and it works well, and is more durable than those 8' whips (I have broken tips off of them too). Cut the extra threads off like it says to do in Jimh's article for a clean look.
posted 01-12-2009 06:27 PM ET (US)
Good setup. Well done!-
posted 01-21-2009 02:17 AM ET (US)
For power boats, such as our Boston Whalers, I have found the 8', 6db antenna to the best option.
The 6db antenna has a very focused horizontal angle (+ or - 35 degrees) .
Your 25 watt, fixed mount, VHF radio signal will carry greater distances with a 6db antenna than it will with the less focused 3db antenna.
The 3' , 3db gain antenna is best suited for sailboats.
Mounted on the top of the mast these antenna pitch dramatically as the boat heels from side to side. The wider horizontal angle (+ or - 80 degrees) of the 3db antenna allows it to maintain a strong signal during this pitching motion.
8db and 9db antenna are also available, however they are 14' and 23' long respectively and are not well suited for boats under 40' in length.
For Boston Whaler owners looking to equip their boat with a quality antenna at a reasonable price I suggest they purchase a Shakespeare 8', 6db antenna.
I confess that as a "West Marine" employee I am partial to "Shakespeare" antenna's.
On a final note always remember to put your 8' whip antenna down before trailering your boat. I have lost count of the number of antenna's that I have sold do to mishaps with low clearance highway underpass's!
posted 01-21-2009 08:54 AM ET (US)
I look closely at the vertical radiation angle and the gain of typical marine antennas in another article:
VHF Marine Antennas
In my opinion, the most important aspect of the antenna on a small boat is its height above the water. Most of these 8-foot fiberglass antennas have to be mounted on the gunwale of the boat, which means they are mounted very low. If you have a radar arch and it has enough strength to carry the mount for an longer antenna, then they are a good choice.
On boats where the antenna is going to mounted on the deck level or on the side of the console, it is more important to elevate the antenna as high as possible. Because of the size and weight of most of the 8-foot fiberglass antennas they cannot be mounted on an extension mast.
Having taken apart a few 8-foot antennas to see what was in them, I have found that often the upper 8- to 12-inches are just empty fiberglass. And the actual radiator portion is no longer than 36-inches, an electrical half-wavelength. You can get the same performance from an antenna like the GAM SS-2 by mounting it on an extension mast. You may even be able to carry it higher. Electrically an antenna like the GAM SS-2 is equivalent to many of the 8-foot fiberglass antennas being sold. In actual test measurement, it produced a stronger signal than many 8-foot antennas.
Some of the 8-foot antennas really don't contain anything more than a 36-inch radiator inside an 8-foot fiberglass tube. Now that is not a bad thing, as it gets the actual antenna as high as if you mounted the smaller antenna on an extension mast.
On the 8-foot antennas that actually contain a longer antenna, when mounted low you have the problem of the lower portion of the antenna transmitting into the surrounding structure of the boat, such as the console, the seats, the metal frame of the Bimini top, and often the radio itself along with other electronics.
Antennas like the GAM SS-2 offer many physical advantages over the usual 8-foot fiberglass antenna. They don't fracture when striking an overhead object. They can be replaced in modular form, if something breaks. And the extension mast is useful as a flag mast. These are all mechanical advantages.
posted 01-21-2009 02:03 PM ET (US)
If you have the opportunity drop by one of the 340 West Marine stores. They have an elaborate Shakespeare display with 12 antennas. To better illustrate the contrast in the core elements and fiberglass poles they have cut a cross section from each antenna.
I found the Shakespeare display very enlightening. Examining the Shakespeare Galaxy 5400-XT 8-foot antenna you can actually see the brass and copper element that runs inside the length of the 8-foot antenna.
The quality of the Urethane-coated fiberglass pole also plays a part in the longevity of the antenna and your comfort level. A poor quality coating will break down after several years of UV exposure leaving bare fiberglass strands exposed. If you slide your hand down one of these weathered antenna you will pick-up painful fiberglass splinters.
posted 01-21-2009 10:34 PM ET (US)
The antenna should be mounted on the console on a center console boat to keep gunwales as open as possible for fishing.
posted 01-21-2009 11:37 PM ET (US)
I have disassembled two Shakespeare 8-foot antennas. I found one of them was made just of the small diameter coaxial cable. The other had some portions of the antenna made from a 5/32-inch diameter brass tube. In both cases the radiating portion of the antenna was about 36-inches long.
I described my findings of the construction of these antennas in previous articles here in SMALL BOAT ELECTRICAL.
VHF 8-Foot Antenna: What Is Inside
VHF Antenna: Shakespeare 5206C
The notion that either of those antennas could produce 6-dB of gain is held only by the advertising copywriters or salesmen at marine stores.
posted 01-22-2009 09:38 PM ET (US)
As a Broadcast Engineer with an interest in telecommunications you are certainly the person to answer any and all questions regarding VHF radios.
That said you have shaken my very faith in the “Good Catalog”!
Not unlike the agnostic, insomniac, dyslexic who would lay awake in bed at night staring at the ceiling wondering if there truly was a DOG.
This afternoon I called Chris in the Tech Support department of Shakespeare.
What he told me was that the delimiter determines the DB specification.
I then turned to a publication that is written for the laymen,
In the “Practical Sailor”.Vol 33, No 3, March 2007 edition they compared 10 different VHF antennas from Comrod, Digital Antenna, and Shakespeare. Their conclusion, in the 8ft, 6-db category, was that the Shakespeare 5225 XT antenna earned their Budget Buy honors. They also recommended the Comrod Digital 529 VW antenna with its exceptional range and top-quality construction.
posted 01-23-2009 01:09 AM ET (US)
In my opinion, Shakespeare makes some fine antennas. I think I have a 5225 XT on hand. I plan to make some comparative measurements about its performance at some point in the future. I won't be breaking it apart to find out what is inside, however, as it is in great condition.
I'll look for the display of Shakespeare antennas the next time I get over to WEST Marine.
For a discussion of isotropic antennas, see
posted 01-23-2009 10:38 AM ET (US)
The Shake 5206-C and 5101 are both inexpensive antennas.
The 5225-XT is about 3x more expensive. It will be interesting
how they compare.
posted 01-23-2009 11:28 AM ET (US)
I am confused by the citation of the recommended antennas as a "Comrod Digital 529 VW." I believe that COMROD and DIGITAL are separate companies or brands of antenna.
posted 01-23-2009 12:53 PM ET (US)
You are correct Digital Antenna Inc. and Comrod are separate companies.
The actual quote from "Practical Sailor" was:
They went on to say:
The Comrod is built to last, and we recommend it.
In this photograph you can see a close-up of 4 Shakespeare antenna models (from left to right) 8300, 8500, 8700, & 8900 . They have cut away an area of the outer shell to show the core in each antenna.
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