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VHF Signal Booster

Old 11-30-2003, 06:44 PM
  #1  
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Does anyone know where you can purchase a signal booster for a marine vhf. Boat in Sea of Cortez, not illegal there. Tried Consumer Marine Electronics, WestMarine, etc. Anyone have one? How do they work? Thanks
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Old 11-30-2003, 07:40 PM
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You are asking about an RF amplifier. No Marine store is going to have one as 25 watts is the maximum legall output in the U.S.
Try a google search for an amatuer radio shop near you. You are looking for a linear amplifier covering approximately 150 to 170 MHz.
You may also find one on Ebay. There is also an "Ebay like" site specifically for Ham radio equipment. I can't think of the name of it right now but I will try and find it and post it later.
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Old 12-01-2003, 07:55 AM
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http://www.tessco.com/products/inv_d...?selsku=486134

tessco has some other models. Check the specs for input/output power. 150-174 MHz.

Dave
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Old 12-01-2003, 09:20 AM
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They show up pretty frequently on E-Bay, about one every couple of weeks. Lots of times they don't even sell.

I do hope you know that using one of these things is illegal as sin (in Mexico too, but not at all likely you'd ever be in jeopardy of prosecution for using one anywhere) and you do not gain one inch of range by using one.

Thom
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Old 12-01-2003, 02:23 PM
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Take a look at these links.

http://cgi.ebay.com/ws/eBayISAPI.dll...&category=1502

http://cgi.ebay.com/ws/eBayISAPI.dll...&category=4671

http://cgi.ebay.com/ws/eBayISAPI.dll...&category=1501
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Old 12-01-2003, 04:08 PM
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It was suggested I get one to extend my range. That would be the only purpose. This area of Mexico is sparcely populated. More range would give an extra margin of safety. I always thought more watts = more range. Am I wrong?
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Old 12-01-2003, 04:54 PM
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Yes, you're wrong. More power will not give you any more range at all. The limitation is antenna height because FM signals which happen to be about 2 meters long operate by a principal called line of sight. Simply put the only way to increase your range is to get your antenna up higher, the 25 watts you have available to you will suffice for any height of antenna you could possible utilize.

Thom
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Old 12-01-2003, 05:28 PM
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Thom,
If he wants more range shouldn't he be thinking SSB.
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Old 12-01-2003, 06:19 PM
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Thom, I'm just currious... Why does the NEW Monongahela NOAH weather station (3) broadcast at 300 watts? and why does Louisville Kentucky broadcast at 27o watts? I know the kentucky CC has a large antenna but what does watts and mhz have to do with it?

P.S Did you know Mon county has its own station now?

sloopy
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Old 12-02-2003, 05:26 AM
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Sloopy,

When the FCC licenses a station, or in this case more properly licenses an antenna, many thngs are taken into consideration. Not the least among these are the base height of the antenna to be built as well as it total height and applied-for power output. These are compared to competing signals on the same frequency, because channel 3 is channel 3 all of the time and there are other stations transmitting on it.

There is also the notion that Federal agencys do not have to comply with the mundane licensing procedures of other Agencys. That is simply not true in most cases and even in the ones where an agency is expempt from licensing requirements its is usually the case that voluntary compliance, in consultation with the issuing agency, will almost always be provided.

You may have noticed above that I said that the power of 25 watts was sufficient to reacj any range that the antenna height on a small boat (or even a large one) could support. Well, that's fine if the antennas in question are only 10's to maybe 50's of feet above sea level, but when the antenna might be up there a thousand feet (an antenna mounted east of Morgantown could easly have a height of greater than 2,000 feet) or more the line of sight becomes very long indeed. Now put that in to competition with an antenna in some place like Friendsville, MD, or Columbus. OH (I don't know if those towns actually have stations, I just pulled their name out of a mental hat) which might also have quite high antennas and the only way the FCC has of reducing interference is to regulate their power output. They can do that because at some level the power output does become the limiting factor, just not out there on a small boat.

By the way, if you want a real learning experinece in paperwork go to the FCC site and take a look at the information that must be provided to support the building of a new high power antenna, now add a Federal Agency into the mix where NEPA documentation must be provided, which will include consideration of radiation patterns and their effect on virtually every living thing, and some of the concerns associated with antenna placement become more understandable.

Thom
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Old 12-02-2003, 07:09 AM
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The earth is curved. Radio waves are not. The max range of a 25W VHF is 15-20 miles, assuming the center of your boat antenna is 10' off the waterline, and the receiving antenna is 60-110' above the ground.

If you quadruple the power, your range will be doubled... but then the receiving antenna has to be over 500-600' above the waterline. Boat to boat line of sight is only about 8 miles and boat to ship maybe 10 miles, well within the range of a 25W radio.

If you're in a sparcely populated area, you need an EPIRB.

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Old 12-02-2003, 07:12 AM
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More power will allow you to broadcast over other VHF radios within your "line of sight". So, you can be heard over other boaters in an emergency. As a matter of fact, there are lots of boats out there with the ability to dump out 100 watts. Not legal but if its not done often, no one complains.
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Old 12-02-2003, 08:34 AM
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Yep,

If you find it important that your signal get though over top of everyone elses, presumably because your emergency is of greater importance than anyone else's emergency, then power is the way to do it.

I have no idea where 150 sport came up with the contradictory opnion that first there was a limitation because of the curvature of the earth (true), followed immediately that somehow by quadrupling your power you would double the range (dead wrong). What? Do increases in your power output flatten out the earth?

It is also utterly wrong to just arbitrarly state that the maximum range is15 or 20 or any other set milage. It is exclusively a matter of antenna height and the formula for determining it is to find the square root of each antenna separately, multiply that number by 1.54 and then add the two sum resulting numbers together to get a range in miles. If you compute that for a typical trailered boat on one end and a typical Coast Guard antenna on the other end you usually come out to a range somewhere in the mid-20-mile area. It hasn't got a thing in the world to do with power though, its antenna height and nothing else.

There is a way to get more power without going to an amplifier though, and that is simply to buy a higher output radio. Many of the 2-meter radios sold all over the place can be modified to cover the marine band, and the modifications are simple. You can then use the HAM radio's higher output if you choose to. As an example I have an ICOM 2-meter radio in my truck that has a power output of 55 watts. The radio has been modified (the removal of a single diode is all there was to it) to work on the marine bands and it also has 100 memory presets, so I have the major marine channels saved and named as MAR-1, MAR-16 and so on. I only use it to listen of course, but one time when I was having difficulties with my main radio I used it for a day (I have put the same molex plugs on all of my radios so they are all interchangable.

Thom
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Old 12-02-2003, 09:41 AM
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Thom, you are confusing line of sight and range, which is dependent on signal strength at receiving end. Read my post again and you will note that I said the receiving antenna would have to be very high to take advantage of the range of 100W over 25W... nuthin' contradictory about that at all. And yes, a 100W transmitter would give about the same signal strength as a 25W at twice the distance.

You are dead wrong about antenna height and nothing else. Signal strength is especially critical with FM, where signal to noise ratio goes to hell quickly at lower signal strengths, when the signal voltage in the receiving radio's IF section drops below the limiting voltage. The S/N curve is shaped like a knee, rather than being linear.

I never set any absolute distance limit. Assuming your antenna is a 12' and the ground station is 200', line of sight tells you that's about 25 miles (5 for you, 20 for the ground station), but I wouldn't bet my life on it with 25W.

OTOH, 15 miles, to a ground antenna as low as 50' is a much safer bet, and 20 miles to a ground antenna 110' up is about all I'd count on. At these longer distances, power and antenna gain, not just antenna height, are factors in the readability of the received signal.

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Old 12-02-2003, 10:29 AM
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Hey guys,

I just found this quick "Line of Site" Calculator on another site.

http://www.vwlowen.demon.co.uk/java/horizon.htm
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Old 12-02-2003, 10:38 AM
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Looks like the same one as the one I use here:

http://www.qsl.net/kd4sai/distance.html

Nice collection of scripts at that UK site:

http://www.vwlowen.demon.co.uk/java/index.htm
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Old 12-02-2003, 02:39 PM
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I can confirm the average maximum transmit of my vhf marine radio on most days is about 10 - 15 miles. But what about those rare days when I can clearly communicate with boats that are more than 50 miles distant. Very rare, but happens.
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Old 12-02-2003, 05:22 PM
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It's called "skip" and occurs when your radio signal bounces off the atmosphere and returns to earth (and sometimes repeats that process).

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