VHF antenna for sport boats

spikedaddy99

spikedaddy99

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Jun 11, 2008
2,615
Prentice, Wi
Boat Info
2005 500 DB
Engines
QSM-11
I have a friend in the Marine Corps currently in Iraq, so I am asking this question for him. He has a 190 bowrider and wondered how/where VHF antennas are used for sport boats? A 9 foot antenna on a 190 may look silly, so what are his options besides handheld?
Mike
 
Or you could just lay it over at a 45 degree angle to give it a racing look!

No I did not just say that! :grin:
 
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There are also 4' glass antennas. But, the first question would be how far away does he plan on going? Would a handheld work for his purposes?
 
Dennis

I suggested that to him. That would be my 1st choice in his boat. He likes the "installed" look.

Mike
 
Dennis hit the nail on the head. What kind of range does he need? I've got a nice SS one mounted on MS Judy and works great for my needs. Not sure if he has a GPS, but with most fixed mounted VHF units you can interface it with the GPS to give you a DSC functions that you can't get with most hand held units.
 
I had a 2004 MOnterey 190 LS for awhile. I mounted a 4-ft fiberglass antenna to her and it looked great. I usually ran with it down, but could easily fold it up when needed.
 
spikedaddy99 said:
Thanks Chuck. How/where did you mount it? M
Click to expand...

Here is how I've got it mounted.

picture.php
 
I have the same antenna as Chuck and mounted in about the same spot. Works well for my needs.

100_2339.jpg
 
I mounted mine to my bimini top pole. It looks really good to me, and I didn't even have to drill any holes in the boat. This would work for either an 8' fiberbglass or 3' ss whip antena. Plus side is that you can move it up and down, increasing your range as required. On my set-up, I could put my antena as high as 16' above the water!
 
What kind of range do you get on those side mount ones? I've been trying to figure out this same thing for mine. I routinely go offshore to dive, anywhere between 10-25 miles, and anything more than 14ish miles is beyond cell phone range and I have to make sure I go with someone. Do the smaller whip antennas provide range for 25 miles?
 
VHF is line-of-sight. Maybe a little bending, but mostly LOS. Do the math with a short antenna stuck to the side of your boat, and it's not much distance. Maybe 10-12 miles.



Pog Mo Thoin said:
What kind of range do you get on those side mount ones? I've been trying to figure out this same thing for mine. I routinely go offshore to dive, anywhere between 10-25 miles, and anything more than 14ish miles is beyond cell phone range and I have to make sure I go with someone. Do the smaller whip antennas provide range for 25 miles?
Click to expand...
 
Have to agree with Redhook98, if you're going that far offshore often then don't go with the small SS whip.
 
I'm taking a marine electronics course now and we just went over this.

The total transmission distance is equal to the distance the first station can see to the horizon plus the distance the second station can see to the horizon plus approx 15% for atmospheric refraction.

to figure out:

D=1.32 x √H
D= nautical miles to the horizon
H= height of the tip of the antenna in feet above the surface of the water.

or you can use this calculator.:grin:



http://www.qsl.net/kd4sai/distance.html
 
There are actually three (3) variables that come into play that determine the transmission distance of your VHF. They are:

1. Power
2. Antenna gain
3. Height

It seems that all the textbook discussions focus on the "height" part and from experience, the power and antenna gain play a bigger role for boaters. As an example, you can stand on the highest mountain with a 5 watt radio with a 2 dB gain built-in antenna and you are only going to be able to transmit a few miles.

If you look at this fancy diagram, you can see the effect of antenna gain on the radiation patterns from the antenna:

antenna.jpg


Take that cross section shown and the radiation patterns are essentially rotated around the antenna and look like a donut. A small SS whip has a gain of about 3 dB and looks like a fat donut and a 16' fiberglass antenna can push up to 10 dB gain created a stretched out donut. However, the smaller gain antenna is not as sensitive to having the antenna straight up and down like a smaller gain antenna is... Add more power to the antenna, and the distance increases subject to the height.

My experience with a 6 dB antenna is that it'll transmit about 10-12 miles with a 20 watt radio. That is far less than what a height calculator will show... You need a higher gain antenna (9-10 dB) and some serious power to transmit the full "line of sight" that textbooks discuss. My 4 dB antenna on my dinghy is good for about 3-4 miles.

My 2 cents.
 
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