New VHF & antenna questions

Never had to replace a VHF or antenna till now. So, I already purchased 2 Shakespeare Galaxy 6dB antennas, model 5399, and 2 ft extensions. This will closely match the height of my current set up. Looking at replacing older Icom radios with new Icoms (want to match my current cut-outs). Below is from Icom manual and I am a bit concerned.

The installation of this equipment should be made in such a
manner as to respect the EC recommended electromagnetic
field exposure limits. (1999/519/EC)
The maximum RF power available from this device is 25
watts. The antenna should be installed as high as possible
for maximum efficiency and the installation height should be
at least 1.76 meters above any accessible position. In the
case where an antenna cannot be installed at a reasonable
height, then the transmitter should neither be continuously
operated for long periods if any person is within a distance
of 1.76 meters of the antenna, nor operated at all if any
person is touching the antenna.
It is recommended that antenna of a maximum gain of
3 dB is used. If higher gain antenna are required then
please contact your Icom distributor for revised installation
recommendations.

My antennas are mounted to each side of the flybridge and are not 1.76 meters (5.77 ft) above said height. They are pretty much right next to me and I've seen plenty flybridge boats set up the same way. Are we all shortening our lives here or are we ok in that we are not transmitting all that much?

My new antenna is 6dB not the 3dB recommended by Icom. All the other 3dB antennas were smaller in height. If I decide on purchasing this new radio what would be the revised installation recommendations? Or should I look for a new radio that recommends a 6dB antenna?

Appreciate your inputs.

i would venture to say to 80% of boats don't adhere to the recommendations described.

most probably don't read instructions for VHF installations.

The combination of stuff you got should be just fine. On the mounting location thing, you do as well as you can, but on many boats it's hard to really get the antennas away from people. Unless you spend an enormous amount of time transmitting, it's unlikely to be an issue.

The 6dB should be fine on most powerboats. 3dB is more appropriate for sailboats and the radio manufacturer has no idea what boat you're putting the radio into. In simplified terms the higher the dB gain the flatter the plane of energy being radiated from the antenna. Too high a gain on a boat that's not level to the water (like a sailboat) the lower the transmit range to the sides, because the antenna is transmitting up into the sky on one side and down into the water on the other. On a flatter running hull higher gain will give you longer transmit range around all 360 degrees.
It is best to have the antenna above the boat's occupants. The RF energy transmitted by the radio is radiation, not a lot different from X-ray, Gamma, etc so there is a slight cancer risk. There have been reports of people who use their cell phones for hours every day developing brain tumors behind the ear they hold the phone to. But that's a lot longer and closer exposure than you'll get from your VHF. Higher frequency too, and the higher the more the risk. Most of us don't worry about it, there's a lot of things in life with a lot higher risk.

Go with a longer extension, but you may need a support if you do.

The ICOM manual appears to be written by lawyers, not engineers. Note that the drastic warnings in the ICOM manual are based upon 9db installations (shipboard) and not on recreational power boats.

I don't transmit very often and my 6' antenna is ~3' away from my head so I doubt I am approaching any MPE limits. A 6' antenna will give you better range than a 3'. Radio output is limited to 25W. So MPE isn't an issue in my opinion.

Marine radios will take either 3db or 6 db and I suspect most people opt for the greater distance. I have a 3db AIS that can be used as backup to my 6db.

RF energy from your VHF radio is non-ionizing and is reasonably safe. The radiation pattern from your antenna is roughly half way up the antenna itself not including the extension. With the extension installed the area of maximum radiation is well above your head. Also your maximum output is 25w. If it was in the 100's of watts (think SSB) it would be more of a concern.

Comodave said:

Go with a longer extension, but you may need a support if you do.

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Im +1 on this. I have mine extended so the radiation is well above. Also, you get more distance that way.

Thanks for posting guys. Based on what I have heard I have ordered 4 foot extensions to replace the 2 footers. Seems easy enough to get a little bit of safety, not that I am sure I will need it. (I do have the supports already in place for the longer antenna). But really, how much time do we spend transmitting? For me it is usually when I am outside/arriving at new harbor. Minimal time. And now that I know the risks (seems slight) I may decide to use the hand held more often.

I removed all of the antennas mounted to the flybridge on our GB 36. They are a source for water leaks and rot even if you can stand them flopping around. I installed the vhf antenna on the mast head. Makes for a nice clean installation with more height / range. Just run the cable through the chase in the salon’s overhead and up the inside of the mast.
https://defender.com/en_us/gam-elec...AaAdCb8goVatHRrEt9KjgVu72IeUaBpyn85-_0aqoUAwY

I am a big fan of having a 9db on board.

Despite a lot of naysayers, I had one on my own an several small commercial boats I ran and appreciated the extra dbs often. Practical experience is my guide.

Personally Id go with Metz when I will outfit my radios. A properly tuned antenna will give you the best results mounted as high as possible.

Pat T said:

Thanks for posting guys. Based on what I have heard I have ordered 4 foot extensions to replace the 2 footers. Seems easy enough to get a little bit of safety, not that I am sure I will need it. (I do have the supports already in place for the longer antenna). But really, how much time do we spend transmitting? For me it is usually when I am outside/arriving at new harbor. Minimal time. And now that I know the risks (seems slight) I may decide to use the hand held more often.

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Many people use (mis-use?) their radios this way. Hailing a marina less than a mile away when entering a harbor doesn't require a lot of power or range. Rather than using a hand-held, why not transmit at lower power? Probably as good or better than a handheld and you are not holding an antenna next to your head.

That said, it's good to have the power and range when needed especially in an emergency, so I would not go less that 6db for an antenna on a trawler and would even consider 9db if it was easily doable. 6db is a decent compromise for most of us.

In addition to the antenna selection, make sure you pick good radios (personally I stick with Icom and Standard Horizon as the 2 "gold standard" brands outside of $$$ commerical stuff). And use good cable to the antennas, especially if you have a longer cable run. Keeping the run short helps reduce loss in cases where you're using a cable built into the antenna or don't have room to run huge coax.


Cable-wise, the Shakespeare Galaxy antennas come with RG-8X, which is decent cable as long as you can keep the run short. Ideally, if the run is shorter than the provided 20 foot cable, you should cut off their quick connect setup and install a new PL259 yourself to shorten the cable to the needed length. If needing a run over 20 feet, I'd give serious consideration to an antenna that doesn't include a cable and then spending the money on some good, heavy cable. Just stay away from the LMR series coax for marine use, as it's not as corrosion and water tolerant as some other cable types.


Some cheaper antennas come with RG-58 cable, which is pretty bad for losses at VHF frequencies and shouldn't be used for more than a few foot run in my opinion.

I use this one mounted on the mast.

https://www.morad.com/products/vhf-antenna-146-hd

Just a foot note about antennas: Couple of years ago I thought I needed new antennas. Being the cheap person I am, before purchasing new ones I thought I would take them apart and see what magic was inside. Maybe they were hit by lighting or something. What a disappointment. There is nothing inside but single strip of copper wire. I got a piece of 8 foot house electric cable and removed the copper ground wire and installed. Bingo, radio magically came to life. Sealed the ends and reinstalled on the boat. Never knew what the initial problem was. Could have been just corrosion or dust that got dislodged.
Barrie

Yep, a VHF antenna is basically just a length of wire of the correct length. I've made several using 1/2" PVC pipe with a wire up the middle. Cap on the top end and a threaded fitting on the bottom that coincidentally fits a standard antenna mount. All from the big box hardware store for like $10. If you get the length right it works fine. There are frequency vs length charts on Google.

psneeld said:

I am a big fan of having a 9db on board.

Despite a lot of naysayers, I had one on my own an several small commercial boats I ran and appreciated the extra dbs often. Practical experience is my guide.

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I have 9 and 6. Under normal conditions, the 9 gives noticeably better range / performance. Under rough conditions, the 9 becomes broken/choppy on transmit so the 6 does a better job then. Considering that the dispersion pattern is wider on a 6 than a 9, that isn't surprising. To the extent that a VHF should transmit reliably under all conditions, the 6 may be a better choice, especially for smaller/less stable boats.

When I say I am a big fan on having a 9db on board, that just means in addition to a 6 db .

Cruising boat especially with flybridge... redundant radios and antennas. One to do the job when the other cant.

Also a handheld for use in the dink and further backup or convenience.

There is a very small danger of RF burns from being to close to an antenna. At one watt power you can just about touch the antenna with no real effects at 25W max power the recommend distance from the antenna to a person is about 3-4 FT on VHF. I would recommend getting the antenna as high as possible for range. A crappy radio with a great antenna will always outperform a great radio with a crappy antenna. I have two 9DB 8FT antenna mounted on my radar arch - one for each radio. Put your 6db antenna as high as you can and with a new Icom should be fine.

Dajinka said:

There is a very small danger of RF burns from being to close to an antenna. At one watt power you can just about touch the antenna with no real effects at 25W max power the recommend distance from the antenna to a person is about 3-4 FT on VHF. I would recommend getting the antenna as high as possible for range. A crappy radio with a great antenna will always outperform a great radio with a crappy antenna. I have two 9DB 8FT antenna mounted on my radar arch - one for each radio. Put your 6db antenna as high as you can and with a new Icom should be fine.

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Not sure I have seen a 9db 8 foot antenna.... what brand/model if you don't mind?

psneeld said:

Not sure I have seen a 9db 8 foot antenna.... what brand/model if you don't mind?

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Oops 6dB. I goofed.

I looked at 9db but it’s big!!!!

Dajinka said:

Oops 6dB. I goofed.

I looked at 9db but it’s big!!!!

Click to expand...

OK....thanks