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Author Topic:   Montauk Antenna Location
stagalv posted 01-19-2001 10:13 AM ET (US)   Profile for stagalv   Send Email to stagalv  
Just bought one of the Shakespeare 3' stainless whip antennas for my VHF. I planned to install it on the console rail. Has anyone had this same rig on your console. Does it ever come back and slap you in the face while you are bouncing around? Rex
Wild Turkey posted 01-19-2001 03:00 PM ET (US)     Profile for Wild Turkey  Send Email to Wild Turkey     
I have the same 3' SS Ant. on my Montauk. I have it mounted on the console rail also. No problem with face slap. However not the same story with my old 6' VHF ant.
Dick posted 01-19-2001 08:10 PM ET (US)     Profile for Dick  Send Email to Dick     
I have the same 3" SS antenna with the rail mount on my Montauk. No problems and works great
Dick
whalerron posted 01-19-2001 10:24 PM ET (US)     Profile for whalerron  Send Email to whalerron     
How well do the 3 footers work? I read that the 3 footers are designed with a different transmission pattern which is ideal for sailboat masts. Because sailboats heel so far over, standard VHF antennas don't work well because they need to be vertical. The 3 footers work good at most aspect angles but because of the lack of gain, they need to be mounted very high. The 8 foot antennas have much higher gain because of their transmission pattern. Because VHF is only good for "line-of-sight" transmission, I was told when considering a 3 footer that it would be better to buy a handheld VHF whose antenna would be 6 feet off the deck while I was using it. Do you guys have any practical experience with this stuff?

thanks
ron

jimh posted 01-20-2001 01:08 AM ET (US)     Profile for jimh  Send Email to jimh     
Poster "whaleron" raises a number of questions regarding the differences between VHF Marine band antennas, mainly those 3-feet long and those about 8-feet long.

All marine band antennas are REQUIRED BY FCC REGULATIONS to be vertically polarized.

All transmissions are subject to the same propagation conditions. The antenna cannot affect the propagation characteristics. These are determined by atmospheric conditions. Once electro-magnetic waves have left an antenna and are propagating through the atmosphere, they all behave similarly. The waves do not remember they came from a particular kind of antenna and therefore propagate better or worse than other waves.

Range at VHF Marine frequencies is basically line of sight. More accurately, your radio horizon is:

range(miles) = 1.2 * SQRT[ height(feet) ]

The "height" is the height on the antenna above the water, not its length.

All antenna "gain" is obtained by concentrating radiation in a favored direction and reducing it in an unfavored direction. Therefore antennas which have higher gain have narrower lobes of radiation.
In general, the favored direction is toward the horizon. The unfavored direction is skyward.

In marine service, when the antenna is subject to motion and movement away from vertical, antennas which have narrow lobes of radiation may not be as effective as ones with broader lobes. Very rapid changes is signal strength may be observed on signals coming from stations where the antenna is rapidly moving out of vertical. This is called "whip flutter."

The difference in antenna gain between two antennas, one 3-foot and one 8-foot, is probably less than a ratio of 1:2.

In most cases, establishing communications at a particular distance will be more limited by range factors due to antenna height than by signal strength due to variation in antenna gain. In other words, it is highly unlikely that two stations that are in range of each other in a maritime situation would be unable to maintain a communications circuit because of lack of signal strength from the tranmitter. The FCC regulations have permitted VHF Marine band stations to have a maximum 25-watt transmitters because that power level will provide excellent communications over the typical path between two stations in that service.

If the typical marine band communications path required more power to ensure adequate communications, the FCC would have allowed stations in this service to have more power.

The FCC engineers have researched this problem and crafted the regulations accordingly.

The regulations only limit the transmitter
power, which may be enhanced with use of larger antennas. However, as mentioned above, gain from antennas is not free. It comes at the expense of reducing the pattern of radiation from the antenna into narrow lobes, which may or may not actually enhance the performance of the transmission circuit path.

--jimh

triblet posted 01-20-2001 02:10 AM ET (US)     Profile for triblet  Send Email to triblet     
I have an 8' antenna mounted on the side
rail of my Montauk.

1. An 8' antenna is going to have a height
greater than a 3'

2. It isn't strictly line of sight. I can
talk from Monterey Bay to Carmel Bay,
through/over granite several hundred
feet high and a couple of miles thick.

3. I can also exceed that radio horizon
number comfortably. Assuming the radio
horizon is measured from the center of
the antenna, mine is about six feet above
the water, so my radio horizon would be
3 miles.

And as long as your boat isn't rocking too
much, the 8' antennas work fine.

Chuck

bdb posted 01-20-2001 09:00 AM ET (US)     Profile for bdb  Send Email to bdb     
I have used 3 and 8 footers on the same rig, and...bigger is better. Had an 8' on a 21 dump-truck and switched to a 3' to clear bridges etc. Transmission and reception drop-off was incredible. Initially thought my radio had died! Went back to 8'.

Went thru same situation with my Montauk. Now have 8' mounted on console rail. In practical application, on my waters, there is a remarkable difference.

3' performance is particularly poor if your area contains islands, cliffs or locks.

Harpoon Harry

jimh posted 01-20-2001 10:34 AM ET (US)     Profile for jimh  Send Email to jimh     
Chuck,

Your radio horizon might be only three miles, but you have to compute the other station's horizon, too.

If you're talking or listening to a station with an antenna at 300 feet (typical Coast Guard or Weather Radio) they have a much longer horizon.

The radio circuit is the sum of the two horizons.

Radio signals at VHF frequencies don't penetrate granite very far. Your signal is probably being propagated by some difraction or scattering phenomena.

Enhanced propagation occurs frequently due to atmospheric conditions, particularly when there is a strong temperature boundary layer in the atmosphere, as might occur with stable air above stable water.

Here in SE Michigan we often get VHF television signals propagating across Lake Erie from stations in Cleveland, a path much greater than that predicted by the equation I cited above.

--jimh

whalerron posted 01-20-2001 11:01 PM ET (US)     Profile for whalerron  Send Email to whalerron     
So, before I go buy an antenna in the spring, what do you guys recommend, a 3 footer or an 8 footer? I will spend most of my time in the Chesapeake and its tributaries and that means the possibility of lots of land and islands between me and the guy I am trying to talk with.

thanks,
ron

jimh posted 01-21-2001 01:31 AM ET (US)     Profile for jimh  Send Email to jimh     
Ron,

It is funny, but the really high-quailty 3-foot antenna (which is used by the Coast Guard) costs more than the 8-foot antenna!

On both of my Whalers I have an 8-foot fiberglass antenna. There are just more of them available and the price is pretty low--$25--so that is probably the way to go.

I would be leery of the 3-foot stainless steel whip antennas; they could be an awful thing to poke your eye out on in rough weather!

--jimh

kingfish posted 01-21-2001 08:28 AM ET (US)     Profile for kingfish  Send Email to kingfish     
$.02 from the peanut gallery-

I very successfully and very effectively used 8' antennae with rail-mount fold-down brackets on both my Montauks. One as per Whaler recommendations, on the vertical leg of the rail all the way aft on the starboard side, the other also on the starboard side, but on the aft vertical leg of the bow rail, just about even with the center console. With that one, I used a cable clam to come out of the side of the console, and fabricated some teak "guards" to protect the cable as it passed over the deck betwen the console and the gunwale. I really liked that installation better; it was out of the way of the Mills suntop, and if I was alone and wanted to drop the antenna in a hurry, I didn't have to leave the helm to do it.

John

triblet posted 01-21-2001 03:19 PM ET (US)     Profile for triblet  Send Email to triblet     
The West Marine Catalog lists the following
8' VHF antennas, all glass.
159363 $100
1185479 $140
567159 $ 30
548438 $ 37
404510 $ 40
404650 $ 46
487721 $ 50
159306 $ 90
1185438 $ 90

And the following 4' antennas. The first
is glass, the remainder SS.

1186097 $ 85
165414 $ 40
110189 $ 45
251442 $ 42
382773 $ 60
1185537 $ 50

I don't see how you can say that the 3' SS
antennas are more expensive than the 8'
antennas. There are three 8' antennas that
are more expensive than the most expensive
3'.

Chuck

jimh posted 01-21-2001 04:22 PM ET (US)     Profile for jimh  Send Email to jimh     
What I should have said:

They only make a 3-foot fiberglass antenna in the high-quality/commercial grade line.

Thus it costs more than the garden-variety 8-footer.

--jimh

andygere posted 01-22-2001 11:33 AM ET (US)     Profile for andygere  Send Email to andygere     
John (Kingfish),
Your installation sounds really trick, do you have some photos you could e-mail or post? Also, you mentioned compatibility with a Mills sun top, would this also be true for a flying top with dodger and curtains? Finally, what is the advantage of rail mount over console mount (bolted with backing plate)? My '79 owners manual suggests the bolt-on method, but perhaps good rail mounts weren't available then.
triblet posted 01-22-2001 01:26 PM ET (US)     Profile for triblet  Send Email to triblet     
One advantage of rail mount is that can fold
flat against the rail or gunwale for
trailering. And the antenna is farther from
other electronics. And, for ME, as a diver, it's
more out of the way. I suspect a fisherman
would find a console mount better so it
wouldn't get in the way with a fish on.

Chuck

andygere posted 01-22-2001 03:16 PM ET (US)     Profile for andygere  Send Email to andygere     
Chuck,
You're right about my concerns with a rail mount: It would be in the way for casting and while fighting fish. For now I'm just using a hand-held radio, but I know my range with it is limited. Also, the holes are already in my console for the bolt-on style mount. It would be easier to reuse these than to fill/fair/gelcoat them (I have SS screws and finishing washers covering the holes now). To me, it seems like the 8 footer is the way to go in any case.
kingfish posted 01-22-2001 08:20 PM ET (US)     Profile for kingfish  Send Email to kingfish     
Andy-

My reasons for rail mounts were first to get out of the way of the sun top, and second as Chuck mentioned, to be able to neatly stow when trailering. If I were not going to use a top, I would probably mount the antenna on the console, but I'd still use a ratchet mount so I could fold the antenna down at will.

I'm sure either of the rail mounts I described would work with the Mills flytop, however the midships mount might have to be coordinated somewhat. As you know, the rails on a Montauk are inside the gunwales, which means the frames for the top are outside the rails, as the frames secure on top of the gunwales. I had a quick disconnect pin on the hinge slides for my suntop, because when the top was up, the hinge slide was outboard of the antenna, but the antenna still cleared the fabric of the top because of the inboard slope of the frames. The antenna sort of went up through the tube work.

My sister owns that Montauk now, and I will see if I can get a photo or two; might take a little time. If you are interested, e-mail me and I will put together a narrative description of how the whole thing worked.

John

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