vhf antenna

[MASTER Brian]

I recently purchased a VHF Marine Band Radio and I am getting ready to install it in my boat. My problem is that I don't want some huge 8' antenna sticking up as I am only using this on smaller (5-10 miles across) lakes and I have a 17' Ranger Fish/Ski boat.

It seems that all I can find locally is about 8' long antenna, so I'm probably going to have to order something. Any suggestions?

What is a good size, height wise antenna for a smaller boat? Also, the radio's manual states not to place the antenna within about 3' of people and NOT to come into contact with the antenna while transmitting. Why is this? Are they really dangerous...I have a 3year old and again this is a relatively small boat, so the 3' thing might be tough.

Also, what are the differences between the VHF antenna and a CB antenna. I can get a small 3-4' whip antenna at Radio Shack for about $20 and it uses the same plug. A 4-5' VHF antenna online looks to be about $80-$100.

 

[MASTER Brian]

Re: vhf antenna

One other thing, I am pretty certain my radio's owners manual states not to use more than a 3db antenna. I mention this because I have been doing some reading on a "VHF" search on here and see a lot of talk about using 6db antenna's.

After doing some research, I guess, I shouldn't ask, what's a good size, as I know some will say the taller the better. I do have a bimini top, I could mount this to, but it's not always up. Would it work at all, if I mounted it to the top, but didn't put the top up? What about if, when I put the top up, I don't stand the antenna up, I just leave it laying horizontally across the rear support.

I guess I'm looking for something that is going to give me decent reception, but not look "out of place" on a Ranger Fish/Ski boat. I feel an 8' antenna always sticking straight up will look out of place.

 

[Ravman]

Re: vhf antenna

this looks to be the one you want.

http://www.iboats.com/Shakespeare_36_3db_Low_Profile_Vhf/dm/*******.785962664--category_id.248106--list_time.1211716598--**********.962947548--view_id.2307

 

[Gary H NC]

Re: vhf antenna

A CB antenna is a big no for VHF. I have the 8 ft with a ratchet mount that folds it down along the gunnel when not in use.The 3 ft will work ok for a couple miles.

 

[dingbat]

Re: vhf antenna

VHF is line of sight communications so the taller the antenna and the higher you can mount it above the water the better.

Going from 8'-3' cuts your transmission distance in 1/2. With a 3' antenna mounted 3? above the water line your radio horizon is roughly 3 miles. Mount an 8? antenna that same 3? above the water and your horizon increases to 5 miles. .

 

[Ravman]

Re: vhf antenna

i posted a link to the 3' whip because he said the manual says not to use an antenna over 3db. i don't believe that there is an 8' antenna made that is only 3db(i could be wrong).

 

[MASTER Brian]

Re: vhf antenna

Thanks for the replies. I measured the width of my bimini and it could handle a 5' antenna. So, if I could get a 5' antenna in the 3db range, then when my bimini is up, the antenna's top point would be up at about 12' from the surface of the water.

Should I go with a whip or a fiberglass one?

Also, on the 3' antenna will that still mount to the ratchet style mounts?

If I go with a 4 or 5' antenna, what would you guys suggest in the 3db range?

I really do appreciate the info, as I didn't realize there was so much to these. I thought they were pretty much a CB radio, with different frequencies for marine use. I guess you learn something every day.

 

[Boatist]

Re: vhf antenna

I never herd of any radio that would suggest you not use a antenna with over 3 db Gain. I suggest you recheck your manual. Also what radio is this?

Normaly the 3DB antennas are used by Sailboat on top of the 25 foot high mast. The reason is they are light and the radation beam is wide enough that even when the Sailboat is heal over can still talk to boats on their beam.

If you want a short antenna then get one. As long as you understand a short antenna also shortens your range. It does make a different but not that big of a difference.
A 3 foot antenna mounted 3 foot above the water would have a range of 3.47 miles. A 8 foot antenna mounted 3 foot above the water would have a range of 4.70 Miles.

For your total range you would need to add the range of the station you are talking to. The forumla is:
The square root of the antenna height times 1.42 = range in miles.


Bodega Bay Weather May 26 a great day to go out.
Winds WNW 290 degrees true @ 9.7 knots with gust to 11.7 knots, Water Temperature. 50.5 degrees F
Seas 3 foot every 10 seconds, Swell Steepness = Swell, As good as it gets.

 

[DRIFTER_016]

Re: vhf antenna

Thanks for the replies. I measured the width of my bimini and it could handle a 5' antenna. So, if I could get a 5' antenna in the 3db range, then when my bimini is up, the antenna's top point would be up at about 12' from the surface of the water.

Should I go with a whip or a fiberglass one?

Also, on the 3' antenna will that still mount to the ratchet style mounts?

If I go with a 4 or 5' antenna, what would you guys suggest in the 3db range?

I really do appreciate the info, as I didn't realize there was so much to these. I thought they were pretty much a CB radio, with different frequencies for marine use. I guess you learn something every day.

I have one of the 3' guys and it works well. Yes they do hook up to a rarchet mount. If you're putting it on your bimini it should be fine and offer good range.

 

[MASTER Brian]

Re: vhf antenna

The radio is a Lowrance LVR-850. I'm pretty sure it's not a very expensive unit as it was actually a gift from a Christmas Gift Exchange with a limit of $100 and I received other items.

With that said, I'm not concerned as it should easily do what I am looking for.

The manual states, "The antenna must not exceed an antenna gain of 3 decibles." Then under that, "WARNINGS: Using an antenna with gain greater then 3 db can damage the radio and exceed the safe exposure limits for RF enenergy....."

The other thing I am curious about is what is the difference in antenna's? Most 3-5' antenna's are $60-80+, but the marina had a 4' whip antenna for $33. I didn't buy it, because I wasn't sure how good it would be. I don't recall the brand....

 

[Boatist]

Re: vhf antenna

Brian

Check out the link below. Lowrance has changed the text to read
"There must be at least 3 db of gain on the Radio antenna".

Also there is another mistake in a later paragraph that they also changed.

It is pretty clear that who ever wrote the incorrect statments is worried about the antenna radiation on people but does not under stand antenna radiation patterns.

Anyway the new statment makes more sense than the old statments.
A 3db antenna has a wider radiation than a 6db antenna and is more likely that people will be in the radation pattern.

As far as antennas goes there is a big difference in the quality and construction of antennas. Cheaper antennas often use just a tuned piece of coax in side. The 3 db antennas usually are a loading coil so the transmiter sees 50 ohms impedence then a 1/4 wave stainless steel whip.

Higher gain antenna are useally fiberglass and inside can just be tuned coax or a brass radiador. The Very flexable whippy type antennas are likely coax.
While they do work they are not as strong and do not hold up as well as a stiffer antenna with a brass radiator.

Some antenna will have filters inside to prevent out of band interference. They are helpfull if your in an area where there lots of strong transmiters, Like San Francisco or San Diego. Of course they cost more and in most area are no better. Antennas that have a nylon base mount and are out in the sun will crack and break over time from sun exposure. The chrom plated brass are fine for fresh water but for saltwater the Stainless Steel hold up better and looks nicer.

In your case Mounting it on your bimini I think will be difficult. Most I have seen are 7/8 inch aluminum. There are mounts made for this but usually for bow rails. Problem I have seen is many really do not tighten down enough to prevent the antenna mount from rotating on the rail and the antenna falls over. So in this case a shorter antenna may hold better as it does not have a much leverage on the mount.

Check out the Lowrance link below for the updated text for you manual.

http://www.lowrance.com/upload/Lowrance/Documents/Manuals/LVR-850_Add_0158-021_040606.pdf

 

[MASTER Brian]

Re: vhf antenna

Ok, I about have this narrowed down. I believe I am going with a 4' antenna, my question at this point, is should I go with:

Digital VHF 4FT 528-VB Black 4.5DB Gold Series http://www.sjkmarine.com/dig528-vb.html
or
Shakespeare VHF 4FT 5401-XT 3DB Galaxy (black)
http://www.sjkmarine.com/sha5401-xt.html

I found a ratchet that should work with my Bimini as it is a 7/8-1" mount.

I didn't link this to the iboats store, as they are out of stock on all the black antenna's I come across and I think black will look the best on my boat. I am also open to other suggestions on the 4' antenna, but do prefer the black, if possible.

Are both of these antenna's capable of sending my GPS location via my radio. That is of course, if I can get my handheld, which is currently feeding my Depth Finder, to also feed my radio.

Thanks again for all the info, I'm actually learning a lot about these through this....

 

[Boatist]

Re: vhf antenna

If you are sure you can get the antenna mounted straight up (Vertical) then I would use the higher gain antenna.

If you can not get it mounted Vertical (straingt up) then go with the lower gain as it has a wider output band.

Yes both antenna cover the entire Marine VHF Band including channel 70.
I would want the Radio connected to the GPS first then if it can do both is ok to conect to the Depth Finder.

The Radio and GPS connection can save your life one day.