[byebye_cable]

Marine VHF antennas at basically 8 foot poles (see link below). An 8 ' pole would *not* store in the bottom of my boat, but if it FOLDED in the middle it would fit nicely.

Is this advisable?

http://www.basspro.com/webapp/wcs/stores/servlet/Product_10151_-1_10001_16025____SearchResults

 

[hkaye]

Don't know. By from I what I've read learning about antennas these types of antennas are usually stacked monopoles to get that 6db of gain. You can search for the phrase colinear-phased or stacked 5/8 wave monopole to find more information on these types of antennas. Such as this -

http://www.ncjrs.gov/pdffiles1/nij/185030b.pdf

These are two monopole antennas on top of one another with some sort of coil or loop in between to adjust the phase.

 

[300ohm]

Bass Pro Shops are pricey. http://www.westmarine.com/webapp/wcs/stores/servlet/ProductDisplay?productId=16014&catalogId=10001&langId=-1&storeId=11151&storeNum=10103&subdeptNum=10278&classNum=10279

I used adjustable stainless mounts, with the quick release lever, on most of the marine vhf antennas Ive had. Like this one: http://www.westmarine.com/webapp/wcs/stores/servlet/Product2_11151_10001_16009_-1____ProductDisplayErrorView
Nylon mounts are much cheaper if using the boat in calmer waters :
http://www.westmarine.com/webapp/wcs/stores/servlet/Product2_11151_10001_98935_-1____ProductDisplayErrorView
You need to lower the antenna to get under some bridges.

Also, when hooking up a marine vhf radio, use thick power cables to the unit, like 4 - 8 gauge stranded to get full transmit power. I learned the hard way 12 gauge just doesnt cut it, heh.

 

[byebye_cable]

Thanks for the feedback. Can anyone dumb down an approach for building a workable antenna - that PDF file is interesting - but I have kids/wife/job! 300, you must know how to build something!

 

[300ohm]

Heh, there are lots of vhf antennas that could be built. However it becomes a question of practicality and durability in a marine environment. A typical vhf LPDA or Yagi antenna would play havoc with the fishing lines, heh.

The marine antennas above have copper coils imbedded in the fiberglass poles, not a very practical thing for DIY building. Also the pole antennas are omni-directional. To get more gain, the antenna would have to be even longer (or directional, which would be a bear holding it in proper position in choppy water).

If you go offshore some distance, you want a good reliable radio setup, so I would stick to the commercial marine antennas and mounts. Shop around, there are cheaper places than the above links.

An 8 ' pole would *not* store in the bottom of my boat

The logical solution is to get a bigger boat.

 

[byebye_cable]

OK, thanks. I don't anticipate going more the a few miles offshore (lake Ontario). What do you think about a hand-held VHF radio - would that do the job?

 

[300ohm]

Yeah, for close in, depending on where the coast guard or other help station or boat is. A cell phone may even have the coverage close in to shore.

 

[hkaye]

Here is a good primer on boat antennas-

http://www.boat-project.com/tutorials/vhfant.htm

Range will be determined by antenna height, gain of antenna and transmitter power. A smaller 3db antenna would only be 3 feet in length.

 

[ota_canuck]

DIY Marine antenna is probably not viable solution.

And here are some other logical solutions for VHF Marine antennas. These are not DIY. You'd have to buy what suites the range yo need, and also consider the storage space you have available on board.
[lengths [email protected] to [email protected] dB]
http://www.digitalantenna.com/vhfantennas.html

An 8 ' pole would *not* store in the bottom of my boat

The logical solution is to get a bigger boat.

Or get a 8ft trailer!

 

[old sparks]

If you have the room (and the battery for it), I would fit a 25 watt radio (with DSC & interfaced with GPS) and the 3 foot antenna (basically a vertical dipole with a sleeve ie. "Bazooka Antenna").

http://en.wikipedia.org/wiki/Dipole_antenna

http://www.hamuniverse.com/vertbazooka.html

This setup will beat a handheld for range anytime. The typical 'rubber ducky' antenna on a handheld is fairly lossy. I've heard it described by some as a 'rubber resistor'.

http://en.wikipedia.org/wiki/Rubber_Ducky_antenna

http://www.tc.gc.ca/publications/BIL/TP9878/PDF/HR/TP9878.PDF

 

[byebye_cable]

Thanks everyone for the ideas. I will research & eventually post results.

 

[byebye_cable]

Here is a good primer on boat antennas-

http://www.boat-project.com/tutorials/vhfant.htm

Range will be determined by antenna height, gain of antenna and transmitter power. A smaller 3db antenna would only be 3 feet in length.

As hkaye notes, a smaller 3db antenna is only 3 feet. This is actually good for a smaller boat. The reception pattern of a 3' antenna resembles a donut (360 degrees) while the reception of the larger 8' antenna with higher gain is flatter (more like a washer). To me at least, it seems like the 3' - while not having the same range - may actually be the better choice for a smaller boat that may be bobbing in the water.

There was a great bazooka DIY antenna idea up there, but I'm siding with 300 that it's probably better to stick with a commercial make for this (safety) application.

So at the end of the day I went with a fixed mount 25 watt VHF radio and a 3' stainless steel whip antenna. $155 + tax & delivery from texpromarine in Port Dover. The owner (John, 67 years young) was the only salesperson I spoke with that I felt confident in, and I couldn't match his prices locally in Toronto. It should arrive next week.

 

[300ohm]

Also, you want to mount the antenna as high as practical.

 

[byebye_cable]

Agreed, I will mount it with a swivel on the top of the cage (which is the higest point).