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ContinuousWave: Small Boat Electrical
Radio Transmitter Installation Recommended Safe Distances
|Author||Topic: Radio Transmitter Installation Recommended Safe Distances|
posted 03-24-2007 08:26 AM ET (US)
I'm reading through the Standard Horizon PS1000 User Guide before I install my new Standard Horizon PS1000 (Black Box) VHF radio in my Montauk 170 console. The manual recommends the following:
1) The antenna be mounted at least 3-feet away from the radio
2) Keep passengers at least 2-feet away from the antenna.
How important are these recommendations? They sell this radio for small boats with limited space. I'd be hard pressed to keep the passengers from getting within 2-feet of the antenna if I mount it on the side of the cc (the place I see them most mounted on Montauks). Also, getting the radio mounted 3-feet away from the antenna when they are both mounted on/in a console that is barely that length to begin with is also a challenge if not impossible (or is it?). I know this radio is very popular with cc boats so I was hoping someone on this site could either
a) Tell me these recommendations are FCC diven (CYA) but not followed in the real world and I should sleep soundly at night. (My 6- and 3-year-old will go walking past the antenna if not bumping into it I'm sure)
b) There is indeed a way to adhear to these recommendations and I just need to be told how.
I should probably let you know I'm mounting the antenna on the cc. I'm not doing a rail mount. Shoot me but that just looks sloppy.
posted 03-24-2007 10:59 AM ET (US)
There are two reasons for these recommended minimum separations between radio, humans, and antenna.
The recommendation to maintain a minimum separation between the radio chassis and the radio antenna is most likely due to concern about radio frequency feedback causing problems with the transmissions. If RF energy from the antenna radiates back to the transmitter, it can cause some undesirable interference with the signal. To minimize this, the manufacturer recommends a minimum physical separation between the transmitter and the antenna.
The recommendation to maintain a certain separation between the antenna and humans is due to concern about electromagnetic radiation exposure. This is really only needed during transmitting. There is proper concern about exposure of human tissue to radio frequency energy. However, given the typical recreational boat installation, the amount of time when the radio will be transmitting is very small, probably less than 00.1-percent of the time the boat is in use. Further, the concern is only probably significant at the 25-watt level of transmission. When transmitting at the 1-watt level the radio frequency energy is probably insufficiently powerful to cause much concern.
If you are mounting an antenna on the center console, I would step back an extra foot or two when transmitting on that antenna at the 25-watt level.
For me, there is probably a greater likelihood of injury from physical contact with the antenna than there is from long-term exposure to high levels of radio frequency energy being transmitted. The housing of fiberglass antennas tends to weather and fray into small particles of fiberglass. Also, people are more likely to try to grab a fiberglass antenna than a metal whip antenna.
One of the reasons I like the GAM ELECTRONICS antenna is its construction makes it very clear what part of the device is the radiating element. With all-fiberglass antennas, there is a potential for someone to grab onto the antenna itself as a hand hold or support. No one is going to grab a GAM ELECTRONICS antenna's stainless steel whip thinking it is a hand hold.
Another advantage of the GAM ELECTRONICS antenna installation is that it moves the radiator of the antenna several feet above everyone's head.
posted 03-24-2007 01:30 PM ET (US)
Thanks Jim. Great info as always. That said, if I get a GAM Antenna, and mount it about 4-6 feet up on a mount, the antenna will then be at least 3 feet away from the radio, have better gain (due to added height), as well as getting it up out of the way of humans. Is that fair to say? If so do you recommend any particular brand/device to mount the GAM Antenna to? My minds eye sees the GAM Antenna mounted on top some sort of shaft/pipe similar in shape and size to a glass antenna, and the shaft/pipe is connected at the bottom to the antenna mount on the side of the cc (where I intended the glass antenna to be mounted)
posted 03-24-2007 01:44 PM ET (US)
Jim, I'm reading your antenna write up now. Sorry, I should have read this before posting. Being a born and bred New Hampshirite I had a sense of pride when I read the following from your article at
"small manufacturer in New Hampshire, GAM Electronics, had the perfect solution"
They had me at...
Thanks again for pointing me in the right direction!
posted 03-25-2007 06:18 AM ET (US)
You are right, most 170 Montauk antennas are mounted within 3 feet of the radio and within 2 feet of people. If the proximity to the radio is a problem you'll know it right away because the radio won't work correctly. As to people, it would probably be impossible to get statistically significant data on whether personal injury happens. There don't seem to be any reports of problems (and my dealer has been installing antennas like this on Whalers for years). We've been also hearing reports that cell phones will fry your brain and/or blow up gas stations or airplanes yet no concrete examples are ever given.
I suspect you would have to hold the antenna an inch from your brain or eye and transmit at 25 watts for considerably longer than a normal VHF marine transmission before a problem would occur.
posted 03-25-2007 10:26 AM ET (US)
If you are seriously interested in the safety aspects of exposure to radio frequency energy, the Federal Communications Commission of the United States has investigated the topic and published their findings. I think that as a source of information the FCC will probably be more reliable than anecdotal reports or repetitions of internet folk lore and urban legends. Please see
RADIO FREQUENCY SAFETY
posted 03-25-2007 12:39 PM ET (US)
I'll let someone else's children find out the effects of exposure to radio frequency energy over time. I myself will be mounting a (GAM Electronics) anntenna high above the (Standard Horizon Phantom PS1000) user's guide recommended minimum safe distances for radio and humans.
Thank you again for your continued forthcoming of reliable information.
posted 03-25-2007 12:59 PM ET (US)
In the case of a typical vertical VHF Marine Band antenna, the characteristic pattern of radiation will focus most of the energy toward the horizon, and there will be little energy radiated straight up or straight down from the antenna. Because of this a vertical separation distance will be even more effective than a horizontal separation distance. If the vertical antenna is three feet above your head you will be in a much lower field of RF energy than if the antenna is at your eye level and three feet horizontally from you.
posted 03-25-2007 01:20 PM ET (US)
Here is a table of pre-computed safe distances done by the American Radio Relay League, an organization for radio amateurs. Using the values for 144-MHz from TABLE 4, it looks like three-feet is a good safe value to use for a 25-watt marine radio installation using a typical vertical antenna:
posted 03-29-2007 09:10 PM ET (US)
I think you can still do 5w of radiated transmit power within 1 foot of your head. If you hit the high power option on a handheld VHF, you usually have to hold it within one foot of your head to get a decent pickup from the microphone.
Try finding a place to mount a PS1000 on a 15' Whaler. I think I need a radar arch to use the 25W power setting.
posted 03-30-2007 12:46 AM ET (US)
I think leaving the transmitter at 1 watt is a good idea. You can always bump it up to 25 watts, if needed. Also might be a good idea to put the local function (attenuator) on, especially when in close proximity to other boats. Might save the receiver on your VHF.
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