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Old 11-08-2012, 07:04 PM   #121
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So, refresh my memory. When and why should one select low or high power on one's VHF.
Other than the aforementioned channels that automatically select low power we use high power for everything. Never had a problem, never had a complaint.
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Old 11-08-2012, 07:09 PM   #122
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So, refresh my memory. When and why should one select low or high power on one's VHF.
David, I don't think there are any hard and fast rules, but I use low power for anyone within site and harbor communications. Just habit. We very seldom have to lower our antennae so that is not a problem. Just another advantage of no flybridge.
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Old 11-08-2012, 08:00 PM   #123
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.......... Two "properly functioning" VHF marine radios, on the same frequency, volume level turned up, and within close proximity, line of sight of each other, will hear each other at either low or high power settings.
Unless the squelch is set too high.
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Old 11-08-2012, 08:19 PM   #124
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David, I don't think there are any hard and fast rules, but I use low power for anyone within site and harbor communications.
That's been my practice as well.

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When communicating with another boat, a Harbor Master, bridge tender, marina, repair yard, at close range line of sight of about one mile or less, use low power setting. Lower transmitter power will reduce the propagation distances, allowing more users to use the channel without interfering with each other.
Larry B.
Okay. That's what I was trying to remember.
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Old 11-08-2012, 08:38 PM   #125
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-----------------------------------


When communicating with another boat, a Harbor Master, bridge tender, marina, repair yard, at close range line of sight of about one mile or less, use low power setting. Lower transmitter power will reduce the propagation distances, allowing more users to use the channel without interfering with each other.

Larry B.
The hundreds of islands up here, many of them fairly high, that make long-range VHF communications an iffy to impossible undertaking at best limit our propagation distance automatically. Other than boats in line-of sight range, and there are rarely very many of them at any one time, we almost never encounter communications interference in the San Juan and Gulf Islands and farther north. And using high power is a major help when talking to a boat or marina that's in the "gray" area of poor reception due to the terrain, and of course there is no way to know that in advance.

So we use high power all the time and as a result have been able to reach boats and marinas and harbors when low power would have resulted in no contact.

If boating in more open waters or in areas of dead flat low ground like the ICW appears to be in all the photos I've seen of it, low power could be a big benefit for the reason Edelweiss describes. But using low power here--- and I've tried it a few times--- most of the time simply results in no contact. So we stopped using it almost immediately and simply leave the radio on high power.

We almost never use the radio anyway. We monitor it but we very rarely use it. We only respond to calls from boats we are traveling with or expect to hear from and we almost never have a reason to transmit except to reply to these particular boats or to contact a harbormaster. So it's not like we're blanketing the airways with long-winded descriptions of what we had for dinner the previous evening.
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Old 11-08-2012, 10:45 PM   #126
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That's been my practice as well.



Okay. That's what I was trying to remember.
----------------------------------------------------
The issue of folding the antennae down to horizontal will affect the overall range of the radio at distance, because the marine antennae are usually 3 to 6 db gain. (kind of like the way the light from a lighthouse is focused and projected across the water.) Tip the lighthouse on its side and most of the light goes where???

But it should still work good enough for short range, line of sight, communications, unless the antennae or coax are shorting out.

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Old 11-09-2012, 08:01 AM   #127
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----------------------------------------------------
The issue of folding the antennae down to horizontal will affect the overall range of the radio at distance, because the marine antennae are usually 3 to 6 db gain. (kind of like the way the light from a lighthouse is focused and projected across the water.) Tip the lighthouse on its side and most of the light goes where???

But it should still work good enough for short range, line of sight, communications, unless the antennae or coax are shorting out.

Larry B.
A horizontal antenna will radiate a signal out from the sides just like if its upright. It does not radiate out the tip at all.
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Old 11-09-2012, 01:09 PM   #128
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Isn't a 0db gain antenna omnidirectional? (not like they are common on powerboats)
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Old 11-09-2012, 03:54 PM   #129
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A horizontal antenna will radiate a signal out from the sides just like if its upright. It does not radiate out the tip at all.
But assuming it's laid down front to back or back to front, there will be little or no signal in front of or behind the boat. And that's probably where you need it if you're passing or being passed.

One would think that a boat owner would know to raise the antenna to a vertical position before attempting to use it. Perhaps the manufacturers should put a warning label on antennas. Like the warning label on coffee cups warning that the contents may be hot.


Contrary to what the specifications might lead one to believe, an antenna does not produce gain. There are no transistors or tubes, what comes out is what goes in. What these antennas do is focus the power fed into the antenna in a horizontal plane (in the case of typical marine VHF antennas oriented vertically). The power that would have been uselessly directed directly skyward and to the bottom of the sea is focused parallel to the water's surface for an apparent gain.
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Old 11-09-2012, 04:21 PM   #130
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David, I don't think there are any hard and fast rules, but I use low power for anyone within site and harbor communications. Just habit. We very seldom have to lower our antennae so that is not a problem. Just another advantage of no flybridge.
Don - Now there's a great reason to not have FB!!!

Mark and Eric will like that one...
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Old 11-09-2012, 04:25 PM   #131
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Originally Posted by rwidman

But assuming it's laid down front to back or back to front, there will be little or no signal in front of or behind the boat. And that's probably where you need it if you're passing or being passed.

One would think that a boat owner would know to raise the antenna to a vertical position before attempting to use it. Perhaps the manufacturers should put a warning label on antennas. Like the warning label on coffee cups warning that the contents may be hot.

Contrary to what the specifications might lead one to believe, an antenna does not produce gain. There are no transistors or tubes, what comes out is what goes in. What these antennas do is focus the power fed into the antenna in a horizontal plane (in the case of typical marine VHF antennas oriented vertically). The power that would have been uselessly directed directly skyward and to the bottom of the sea is focused parallel to the water's surface for an apparent gain.
That is a very good explanation of "gain" in antenna systems.
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Old 11-09-2012, 05:03 PM   #132
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A horizontal antenna will radiate a signal out from the sides just like if its upright. It does not radiate out the tip at all.
Just for grins, lay your antenna down and do some "radio check" calls on a suitable channel while turning the boat at various angles to the receiving station and let us know what happens. What kind of range at what relative bearings and at high and low power?
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Old 11-09-2012, 05:11 PM   #133
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That is a very good explanation of "gain" in antenna systems.
Thanks.

That's the "short" answer. Here is more detail:

The West Advisor: VHF Antennas

And for those who do best by looking at pictures (In the computer world we say a picture is worth a kiloword):



Imagine what happens when you lay that antenna down. Where does the signal go?
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Old 11-09-2012, 06:33 PM   #134
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Well, I'm "stuck" with a high-for-a-motorboat sailboat antennae. Should normally give good range but with the high hills and mountains around here reception is fairly limited except for the USCG high-strength signals.

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Old 11-09-2012, 08:54 PM   #135
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Well, I'm "stuck" with a high-for-a-motorboat sailboat antennae. Should normally give good range but with the high hills and mountains around here reception is fairly limited except for the USCG high-strength signals.

--------------------------------
rwidman
Good pic,
(that would be the "lighthouse" analogy, but if you tip a lighthouse over on its side, the light does not come out it's tip.) Now let's hope someone doesn't look at this pic and run out and buy a 9db or greater gain antennae, because they perform poorly on small boats which tend to pitch and role a lot.

Markpierce
You're fine with your antennae, height is good. It should give you excellent service or as good as it's going to get for your area. If you're surrounded by hills and mountains, there is not much you can do about it.

Here in the PNW we're surrounded by hills and mountains too. For my work, that is an advantage as we can string radio base stations and repeaters on top of some high hills 2500 feet plus (I know these would be mountains in some areas, but they're hills here) and serve a large geographic area. Most of our base station sites are running about 50 watts output now and with the FCC mandate to switch to narrow band VHF by Jan. 1, 2013, we'll be lowering that to 25 watts and still cover the same area.

Altitude is king when it comes to VHF propagation. The CG even shares several of our mountaintop sites around the Sound.

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Old 11-09-2012, 08:55 PM   #136
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Using low power on the VHF

We are doing the Great Loop and are currently in the interior river system and about to enter the ICW. These are relatively straight paths, much like highways, with high traffic in both directions. There are many boats (both private and commercial), and they are communicating with each other, and with locks, marinas and bridges.

Under these conditions, I believe it makes sense to use the VHF with consideration for others. That includes use of low power whenever possible and limiting "chat" time. Low power is just fine for almost all communications other than those that are long distance or critical or emergency in nature. In fact, some lock masters ask you to reduce power while approaching and operating in the lock.

How often have you wanted a brief conversation on 68 or 72 only to find someone far away smearing the airwaves with mindless jabbering? Let's all be courteous.
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Old 11-09-2012, 09:12 PM   #137
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How often have you wanted a brief conversation on 68 or 72 only to find someone far away smearing the airwaves with mindless jabbering? Lets all be courteous.
sooooo true. Good point.
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Old 11-09-2012, 11:22 PM   #138
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sooooo true. Good point.
This is correct. How many times have I heard a slow pass radio transaction from 10 miles away? Once you are on another boat's stern you can use low power and not inform every boat within 10 miles that you're passing. On one hand it is nice to know that an extremely polite boater in a sport fisher is approaching, but on the other hand it just blocks up VHF 16.

Just don't chatter on 16 and choose a channel other than what a local marina uses as their working channel and you won't bother anyone. Around here, lots of boats use 17 to arrange slow passes, or just make it short and sweet on 16. The commercial fishermen use 69 and that is a great channel to listen to to see what they are catching, or to hear them bitch about Obama. Entertaining either way.
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Old 11-10-2012, 05:51 AM   #139
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Here is more detail:



Imagine what happens when you lay that antenna down. Where does the signal go?
If the signal only went 100 feet out and 30 feet up that might be a reasonable question but a better representation would show those lobes reaching out for many miles horizontally and quite a few miles upward, not to mention the signal that is reflected off other boats, buildings, hills, and etc.

As far as the lighthouse analogy, if it was a dark and slightly misty night, you would see the glow from a great distance. That is far closer to reality than a focused beam of light in a perfectly clear medium with nothing to reflect or divert any energy away from the beam.

Why not just try it for yourself? Fold your antenna down horizontally and try this - Automated Radio Check Service | Sea Tow
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Old 11-10-2012, 09:56 AM   #140
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Having a 17-22 foot 9db antenna to me is a good safety issue
Most boats who cruise should have one..they work just fine on most of our trawlers as lond as you aren't rocking and rolling more than 30 degrees regularly.
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