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  Distance to People From VHF Marine Band Antennas

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Author Topic:   Distance to People From VHF Marine Band Antennas
krbernier posted 05-11-2010 02:13 PM ET (US)   Profile for krbernier   Send Email to krbernier  
I just finished installing my VHF Marine Band radio. After installing the antenna, I notice a warning in the radio manual saying the antenna should be 2.5-feet away from people to avoid RF exposure. Is this something to be worried about? The antenna is mounted on the front of my Montauk 170 console so it is hard to stay two feet away from it at all times.
whale posted 05-11-2010 07:14 PM ET (US)     Profile for whale  Send Email to whale     
As long as you use it on low [i.e. on the 1-Watt power output setting] you should be fine. That is just like the handheld units.
krbernier posted 05-11-2010 07:54 PM ET (US)     Profile for krbernier  Send Email to krbernier     
It kind of defeats the purpose of a fixed mount VHF [radio] and antenna doesn't it? I typically don't use anything on low.
jimh posted 05-11-2010 08:16 PM ET (US)     Profile for jimh  Send Email to jimh     
The concern for the minimum distance between a VHF Marine Band antenna and humans is only during transmission. SInce 99-percent of the time you will not be transmitting, for 99-percent of the time there is no concern about the distance between a person and the VHF Marine Band antenna.

For the 1-percent (or less) of the time you are transmitting, you should try to observe the recommended minimum separation of 2.5-feet.

It is reasonable to assume that the warning is provided based on the highest power output, 25-watts. If you do not need to use 25-watts, then there is even less concern about the separation of the antenna from humans.

In my opinion, the warning is included as a protective measure for the manufacturer or to comply with recommended safety measures. I would not have a great alarm about transmitting on the antenna for very short periods and only being 2.5-feet away.

If you have mounted the VHF Marine Band antenna in such a way that it is located less than 2.5-feet from the helmsman or from other occupants of the vessel, you are probably degrading the range of transmission from the radio anyways.

David Pendleton posted 05-11-2010 08:18 PM ET (US)     Profile for David Pendleton  Send Email to David Pendleton     
Considering the amount of power your radio is pushing (a maximum of 25w) and the amount of time you'd be transmitting (presumably not very much), I think you'll be fine.
David Pendleton posted 05-11-2010 08:20 PM ET (US)     Profile for David Pendleton  Send Email to David Pendleton     
Apparently, Jim and I were posting at the same time. I think you get the idea.
contender posted 05-11-2010 08:20 PM ET (US)     Profile for contender  Send Email to contender     
I think this is another precaution due to lawyers, The amount of RF that would be required to harm to you, would propably take more than 30years/24 hrs. a day 7 days a week. Some where along the line an attorney took this to court and made a case out of it. So to protect the company they had to post the statement on the box.(just like do not use metal ladders on power lines posted on the side of the ladder). I worked in a field (31 years) that required us to wear a radio 24 hrs (shift) and to this day I have not heard about anyone that has suffered from the RF factor from the city that I worked in. Personally I think you have a better chance of getting hit by lighting...Take care
krbernier posted 05-12-2010 07:41 AM ET (US)     Profile for krbernier  Send Email to krbernier     
I figured it was not really an issue.

I have a 2010 170 Montauk. I mounted the 4-foot Shakespeare fiberglass antenna on the small 2-inch step on the front of my console next to the rod holders. It is the right front of the console. I don't stray too far from shore normally. The radio is a Standard Horizon GX2000. I understand this is not the ideal location for maximum range. The top of the antenna is about 6' off the water, any estimates as to how much range I will have?

jimh posted 05-12-2010 09:01 AM ET (US)     Profile for jimh  Send Email to jimh     
The range of communication depends for your boat is influenced by the range of the station you are communicating with. If you are calling a shore station with an antenna at 500-feet above the water, your range to that station will be much greater than if you call another boat using a handheld radio.

It is not unusual for two boats with 25-watt radios and decent antennas to be able to communicate at a range of about 15 miles, and sometimes more.

jimh posted 05-12-2010 09:02 AM ET (US)     Profile for jimh  Send Email to jimh     
For more on estimating radio range, see


http://continuouswave.com/whaler/reference/pathLoss.html

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