Help With Location of VHF Radio and Antenna

[mtp9302]

Hello all, I am new to boating and confused about the installation of my VHF radio and antenna. I have a 1985 Wellcraft 190 American (19' open bow), and I am currently contemplating installation of a VHF radio/antenna package I bought - a Cobra MR F45 fixed-mount VHF radio with a Shakespeare 5206-N antenna (8', 6 dB gain).

I did a lot of reading before buying and it seemed like this would be a good general-purpose combination for my boat, but I'm confused about the installation spacing requirements I'm discovering. I've read about three requirements that I'm not sure how I'm going to satisfy (I've read about them in many places, but see the attached picture of the radio owner's manual page where they are stated):

- Radio must be 3' away form compass.

- All people must be 10' away from antenna when transmitting.

- Lowest point of antenna must be 1' above everyone's head.

Am I misunderstanding these, or are they just a legal disclaimer that they have to put in there that no one follows?

The compass requirement makes the most sense, but even there the compass is on top of my dash. There is no place at the driver's helm that I could mount the radio, still see it, and be 3' away from the compass. The only solution I see would be to mount the radio on the port side (passenger seat), but I was under the impression the captain should have the most radio access?

I understand that invisible energy is real and must be respected, but if everyone were 10' away from the antenna when transmitting there would be no one in the boat. Also, to mount the antenna over everyone's head it would have to be higher than the windshield.

I want to do the right thing so I haven't installed the radio or antenna yet. I know there are some smart folks on here that have probably set up multiple systems. Do you just do the best you can and then ignore the rules? Any advice is greatly appreciated. Thanks very much for your help.

 

[mtp9302]

Re: Help With Location of VHF Radio and Antenna

I see this was moved; sorry about that, didn't mean to post in an incorrect forum.

Also, it doesn't look like the manual page I was trying to link came through, so here is the manual's location on the web (the warnings I referenced are on p. 30 of the manual, p. 18 of the PDF):

http://www.cobra.com/downloads/manuals/MRF45_MANL_ENG.pdf

Thanks again for any help you can give, and I look forward to your advice.

 

[Boatist]

Re: Help With Location of VHF Radio and Antenna

Welcome to the board

Lots of fourm to post in but will get best results in the one that fits the best.

One other requirment you may see is radio should be 3 feet or more from the radio.

Most of these are just the possibilty of the antenna radation causeing some sort of health problem from long term exposure.

Most that study this possible problem believe if there is a problem it will show up first in cell phones where people use with the transmiter right next to there head and use a lot more than a VHF Radio.

On my boat the antenna is about 3 feet from the compass and the antenna is about 3 feet from the radio. Neither of these has caused any problem on my boat.
The compass does not move when I key the radio and the radio has no feed back from being close to the antenna.

10 feet away and 1 foot above everyone head is not practicle on a 19 foot boat.

If your worried about it them transmit with 1 watt most of the time. Range is not affected very much by transmit power as VHF is line of site.

Example is the DSC button on your radio for emergency distress signal to the coast guard and it transmits with 1 watt on Channel 70.

I would bet that at least 80 percent of 20 foot and smaller boat do not meet all of those requirments.

For best radio range the higher the antenna the better but you have to be able to lay it down when traveling.

On my 20 foot boat I have it mounted in front of the window near where the bow rail starts and it lays down on the starboard gunnel.
When traveling I have a soft cover I put over it and snaps that hold it in place.
This prevents the gunnels and the antenna from getting strached.
Also stops people from getting caught on it when getting in and out of the boat.

If the antenna top is 11 feet above the water then your boats range will be just under 5 miles plus the range of the other station.
Boat to another boat like yours will be about 10 miles.
Boat to Coast Guard with and antenna mounted 3000 feet high will be just over 80 miles.
Coast Guard Rescue 21 system will be set up to here your DSC emergency signal out 30 miles along the entire Coast of the US.

It is ok to Shorten Your Coax but do not go Shorter than 6 Feet. I left mine a about 10 Feet just in case I move the antenna to the other side of the boat it will still be long enough.

After installed if you have a VHF SWR metter test it. Should be less that 2 to 1.
A CB SWR meter will not work on VHF.
If you call the Coast Guard for a test do not call on Channel 16.
Better to call another boat or call the Coast Guard to report something like a floating hazard or a Navagiton light out or DIM.

If you also have a GPS on board be sure to wire it up to the radio and get a Free MMSI number so the DCS distress button will send out a message to other boats and the Coast Guard when you in trouble and hit the button.

 

[mtp9302]

Re: Help With Location of VHF Radio and Antenna

Hi Boatist, thanks very much for your help. I imagine on a larger boat it is a lot easier to get the antenna away from people, but I really don't know how I would do it on a 19' boat and still be on the boat. I didn't want to install this irresponsibly, so I appreciate your confirmation.

I will heed your radio advice about Coast Guard calling and such; I've taken the Coast Guard boater safety course, so I've already heard some of it and I know it's important. No GPS yet, but hopefully someday because I like the idea of something like the MMSI.

Right now I can't decide if I want to install the radio on top of the dash (above the instrument cluster and beneath the windshield) or flush mount into the dash below the instrument cluster (below and to the left of the steering wheel). Both choices put it within about 1' - 1.5' of the compass, which is less than 3' but the compass doesn't move when the radio is there. I guess I'd have to wire up the radio and turn it on to know for sure though, right?

As a result, these radio locations pretty much become a choice between cutting a small hole in the top of the dash for the wires/cable to feed through or a large hole on the bottom of the dash for the radio. I don't feel great about putting holes in my boat, even on the interior. It already has so many holes that I don't like looking at from previous owners' equipment that has since been removed...

The antenna came with 15' of cable, and I was going to coil the excess vs cutting it to length. Unfortunately, on my boat where the windshield ends turns right into the side; there isn't a flat area between the two on which I could lay an antenna down. I thought about mounting it up by the starboard bow rail as well, but when I went to lay it down it would run into the windshield.

I could mount it on the outside of the gunwale; I have some existing, unused holes in the gunwale next to the captain's chair where I could put the antenna mount, but it wouldn't be 3' away from the radio (more like 1' - 1.5').

My fear mounting on its side like this is that the antenna height direction when raised would be 90 degrees off from the mounting plate face. The concern is that this angle would put a lot of stress on that part of the gunwale when the wind is blowing the antenna around. This side mounting would also put the antenna out a few inches from the boat when laid down, which may get in the way of passenger entry/exit.

Not sure where exactly these are going to end up; placing them correctly seems to be the hardest part of installation. Anyone have any advice/pictures of how they did it?

 

[NYBo]

Re: Help With Location of VHF Radio and Antenna

Those sound like the warnings I've seen for radar installations, not VHF.

 

[Boatist]

Re: Help With Location of VHF Radio and Antenna

Mounting is always hard but you will find a way.
Of Course all radios have a magnet in the speaker and also you really do not want wires close to your compass but if with the radio on and transmitting the compass does not move then I think it ok to be pretty close.

My first antenna I mounted on a bow rail but every so offten it would fall over so moved it to about the corner of my windsheild and drilled the holes for bolts with big backing washers.

Coiling you Coax is ok just do not make too small of a coil.

Below a few information Video about DSC Radio.


http://www.youtube.com/watch?v=M-f4nhnBThg

http://www.youtube.com/watch?v=mdkxsWBncSc&feature=channel

http://www.youtube.com/watch?v=JQk5MRwuxgo&feature=channel