VHF antenna selection?

[ted655]

dI just recieved a nice present. A Uniden VHF base set. UM525. Now I need an antenna for it. There are many types, sizes & prices out there. I could use help finding the right one.
It will be used on our HB, so the antenna will mount high up (if that matters). Used mostly om rivers & inland waters.
I have no idea of which antenna I need. W@hat do you suggest? Thanks,

 

[troypolla]

Re: VHF antenna selection?

How high are we talking. The higher the better, and if its not going to be up high make it longer(bigger). I have a shakespeare 8.5 foot. that does me fine. I think the gain is 6dB. was only about 100 bucks. I had to make the connector though. It wasnt hard to do. If you have a soldering iron it shouldnt take more than 10 minutes to make the connections.

Hope this helps

 

[tashasdaddy]

Re: VHF antenna selection?

i have the 8 1/2 shakespeare also, work well for me. heres a formula for range.

http://en.wikipedia.org/wiki/Very_high_frequency#Line_of_Sight_Formula

 

[ted655]

Re: VHF antenna selection?

If it mounts on the cabin roof, above the salon/helm area, that's around 7 1/2'. above deck (9' above waterline). Highest place on the boat.
I see 3db gain to a 10 db gain. Important on an ocean horrison I guess but what's important on rivers?
I don't get the "make your own" connection. For a $100 they don't provide a screw on & go connector?
How are VHF antennas evaluated or rated? What is the difference between cheap & expensive, as far as performance?
Thanks,d

 

[tommays]

Re: VHF antenna selection?

I don't get the "make your own" connection. For a $100 they don't provide a screw on & go connector?

If you do not make your own connection MOST installs would require you to drill REALLY BIG holes VS a tiny hole to feed the cable 8)

And the screw connection would crap out fast in a marine enviroment

Tommays

 

[troypolla]

Re: VHF antenna selection?

Tommays got it. small hole vs. big hole.

 

[ted655]

Re: VHF antenna selection?

The more Db gain of the antenna the more power output?
That formula was Greek to me.

 

[Boatist]

Re: VHF antenna selection?

First the antenna are rated in DB Gain. A gain of 3DB doubles the Efective Radiated Power, ( 50 watts).
A 6 DB gain antenna doubles the ERP (Efective Ratiated Power) again, (100 watts). A 9 DB doubles ERP again 200 Watts.

For most boats a 8 foot 6DB antenna is the best choice. As the gain of the antenna go up the horzional band that the antenna transmites in is more narrow. So if the boat rocks and rolls the signal will drop out with a 9 DB antenna a lot of the time.

Lots of antennas out there and a big difference in quality. I really like the Shakespeare 5225 8 foot 6 DB gain. When I installed on my boat it more than doubled the number of stations I here.

Some Cheaper antennas use a length of coax tuned to the correct frequency for the radiator. They are small in diameter and flex alot so over time the radiator breaks down.

Better antennas use Brass or copper bars for a radiator and they hold up much better. Also 1 inch at the base and taper on the way up but do not flex near a much.

If your boating in salt water get a Stainless Steel mount.
Fresh water cromb over brass hold up very well.
Nylon mount are cheap but over time out in the sun will eventually break if your boat is stored in the sun.

How high to mount? If the top of the antenna is 10 feet above the water then your transmit range is 4.49 miles.
Talking to another another boat rigged the same his signal will also travel 4.49 miles and meet your at the water for a range of 9 miles.

Talking to the Coast Guard out here range can be 80 miles as their antennas are mounted up on a 3000 foot high mountain.

 

[whofan]

Re: VHF antenna selection?

I just bought a 4` "Digital" glass antenna from Iboats For $75.00


The shakspere little giant version from Cabela`s was $104

Everyone says Ditigal is a good brand, its made in USA.

8` antennas are best but on my 16` boat I went with a quality 4 footer.

Iboats has good prices on antennas. Fast shipping too.

 

[ted655]

Re: VHF antenna selection?

8)Thank you very much! Now I know enough to start looking.