Antenna choice

[surrender]

i have a 17' McKee Craft center console. No t-top. What would be a good choice for a VHF antenna? Boat will be used up to 15 miles or so off the beach on nice days. i was thinking a 5' base attached to the side of the console with a 3' whip on top. Anybody have any ideas? Or would a simple 3' whip attached to the handrail around my windshield do about the same thing?

 

[whofan]

Re: Antenna choice

i have a 17' McKee Craft center console. No t-top. What would be a good choice for a VHF antenna? Boat will be used up to 15 miles or so off the beach on nice days. i was thinking a 5' base attached to the side of the console with a 3' whip on top. Anybody have any ideas? Or would a simple 3' whip attached to the handrail around my windshield do about the same thing?

Bought a 4' Digital brand Glass antenna from Iboats a few years back. Works great.

Comprarible to Shakespears Little Giant antenna.

The 3` whip steel antenna is not as good.

 

[surrender]

Re: Antenna choice

Whofan, what part number? How did you mount it? Thanks

 

[whofan]

Re: Antenna choice

Whofan, what part number? How did you mount it? Thanks

http://www.iboats.com/800-Series-4-...4505309--**********.628161238--view_id.356313

or

http://www.iboats.com/800-Series-4-...4505309--**********.628161238--view_id.356312
These don`t come with the cable

This one comes with the cable this is the one I think I have;
http://www.iboats.com/Digital-Anten...4505309--**********.628161238--view_id.359285

I mounted mine on the gunnel with a RAM Mount antenna mount.
http://www.iboats.com/R-A-M-Univers...4505309--**********.628161238--view_id.391369

I only have a 16 foot boat so I went with the 4 footer. Works great for me.

I was really happy with the quality of the Digital Brand antenna.

Iboats have been great to do business with too.


As you know a 8 foot antenna is best unless you need a shorter one mounted up high.


I been told the 3 foot metal or whip antennas are junk in a marine application.

Buy yourself a good antenna.

 

[JoLin]

Re: Antenna choice

good dissertation here:

http://members.toast.net/boatguy/vhfant.htm

VHF electromagnetic propagation is known as Line-of-Sight (LOS). Like a flashlight, it can only transmit in straight lines. This differs from lower-frequency radios in the HF range, such as HF-SSB or Citizen?s Band (CB) radio that can rely on "skip" to transmit long distances. For this reason, the transmission range for VHF marine radios is effectively limited by the curvature of the earth and antenna height. In this regard, the higher you can mount your antenna on your boat, the further you will be able to communicate. Of course, this is simply because the line-of-sight for the higher antenna is greater. There is a mathematical formula that can help in determining the line-of-sight distance:

Distance = square root of (1.42 x Antenna Height)

An 8 foot antenna mounted 3 feet above the water...

D = sq root of (1.42 x 11)
D - sq root of 15.62
D = 3.95 miles

Now, if the receiving radio is configured similarly, that doubles the range to just under 8 miles (3.95 + 3.95). A shore station with a 50 foot high antenna can theoretically receive your transmission at a distance of 12.38 miles (8.43 + 3.95).

 

[jhebert]

Re: Antenna choice

I have had great performance from this installation:

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

I highly recommend using a three-foot whip antenna on an elevated mounting.

I use the GAM antenna because it has the cleanest and best mounting. There is nothing else like it. The stainless steel radiator does not break or crack like those over-priced fiberglass pole antennas.

Antenna height is more important than antenna gain. Put the antenna as high as possible.

 

[jhebert]

Re: Antenna choice

I been told the 3 foot metal or whip antennas are junk in a marine application.

Nonsense.

 

[Boatist]

Re: Antenna choice

JoLin
Very good artical great job.
I would only disagree with one thing. The forumla for range should be.
Square root of the height (in Feet) above water x 1.42 = range in miles.
So in you example of a 11 feet high above water it would be.
Square root of 11 is 3.32 times 1.42 equals 4.71 miles plus the range of the other boat or station.
The 50 foot high range is just over 10 Miles plus the range of the other station.

Small difference

 

[JoLin]

Re: Antenna choice

JoLin
Very good artical great job.
I would only disagree with one thing. The forumla for range should be.
Square root of the height (in Feet) above water x 1.42 = range in miles.
So in you example of a 11 feet high above water it would be.
Square root of 11 is 3.32 times 1.42 equals 4.71 miles plus the range of the other boat or station.
The 50 foot high range is just over 10 Miles plus the range of the other station.

Small difference

Hi, Boatisit- I retyped the formula from the article only because I wasn't able to copy and paste it. Either you're right or the article is, but as you noted, it's a small difference.

 

[whofan]

Re: Antenna choice

Nonsense.

Thanks for the info on antennas. When I was researching antennas I found that the 3` whips were inferior. I know that at the time with certain radio purchases from Cabelas they would give you a 3` whip for free. So I believe they were junk.
I guess if they are mounted high enough they are good.
I was looking for quality so based on my research I ended up with a 4` glass antenna.

 

[JorgeE]

Re: Antenna choice

4' antenna should work fine, especially if you mount it high.
The range will be more than the formula calculates due to "scatter" which spreads the signal a little beyond the theoretical hirizon. Amateur mobile radios operating on frequencies very close to marine VHF can regularly communicate 10+ miles between vehicles, over water should do slightly better (no obstructions).
The 4' antenna will give you 3-4 dB gain, an 8' one would give you even more. The higher the dB gain, the more it will concentrate your radio's power towards the horizon, with less beign wasted vertically. A higher dB gain antenna will also improve your reception by concentrating your radio's "listening power" in the same horizontal direction as the radiated power; sort of like holding a funnel to your ear.
Highest dB you can get, mounted as high as possible, will get you the longest range.
Jorge

 

[Boatist]

Re: Antenna choice

JorgeE
I find the range forumla's to be very accurite over water.
My 6DB gain 8 foot antenna top is about 11.5 feet above the water plus a little more if up on plane. My range to boats set up like mine is very near 10 miles.
MY boat range is 4.82 miles but don't forget you also have to add the range of the other boat.
Higher DB gain does not help your range much on the water but can help you get thru.
9DB gain antenna are usually not recomended for small boat under about 30 feet because they have a narrrow horziontal radation pattern and when the boat Rocks and Rolls the beam will point into the air or water and the signal will cut out. This is more of a problem on large bodies of water or oceans with large swells.
Range to a party boat about 15 miles and to Coast Guard over 80 miles.

Mobile to Mobile in the Ham 2 meter band in a city is not always less than over open ocean. A couple of reasons for this is most will be using more than 25 watt. It is still line of site communication but the signal may refelect off a building 30 stories high.