VHF Antenna lengths

bigeasy1 · #1 01-25-2009, 06:37 PM

I've always run 8' Shakespeare Galaxy vhf atennas on all my previous boats,mostly mounted on the gunnels or side of the hardtop.
For those of you with center consoles with T-Tops,what length antennas are you running?

The reason for the question,is that I installed an arch on my Tsunami,and wonder if because of the tower height(approx 76"above the deck)if i can get away with a shorter one,and still get good range from it.

I'm a bit concerned about mounting an 8' on top of the arch,only because when i trailer it there won't be a lot of support for it when it's laid down horizontally.

The arch is about 30" wide,so there would be at least 6' hanging unsupported.There will be one long trip of 400 miles,to where It will live,then,once it's there, only about a mile to the launch thereafter.

Just wondering what kind of reception i can get from,say,a four foot model.
Any comments would be helpful,Thanks all.

castalot · #2 01-25-2009, 09:54 PM

I've always run 8' antennas with no problems except once i used a plastic mount didn't fare too well in rough seas but once i switched to metal not one problem (it used to be on my 25' pro-line walkaround on a radar arch about 7' from the water line)
matt

Caymanboy · #3 01-25-2009, 10:08 PM

Most 8' antennas are 9db, means you get greater tranmission, the 4's are 4db and the metal whips are 3 db, so if you go with a shorter antenna you will get less transmission and reception range.

McGillicuddy · #4 01-26-2009, 04:19 AM

I use a Galaxy 5225 XT but I too am putting a rod arch and lights on the Seafari. Not sure if I'll ante up right away but when that day comes I'll be looking for one of these:
http://www.diguniverse.com/MARINE-AN...NAS/14100.html

BigLew · #5 01-26-2009, 08:38 PM

John123 andCaymonboy are right, 8' antennas generally get you 9 dB output radius which is genereally farther than 3-4 dB assuming mounting height above the water is approximately the same. I believe that there is a 8-9 dB output 3-4' antenna out there, but I might be wrong. A typical arch will not make that much difference in terms of range in this application. (A 35-65' mast on a sailboat would.)

That said, an 8' antenna on an arch would be ideal, especially if you have a strip of 1 x that you could lash it to during a trailering trip for support. You could leave the wood in the truck/car or at the house/hotel where you stay for the ride home.

Good luck. This is all explained in the 'buyer's advisor' pages in a West Marine catalog, or it used to be anyway.

Good luck.

Tarpun · #6 01-26-2009, 09:58 PM

VHF is line of sight. All things being equal the taller the more range. Most 8' VHF antennas such as Digital and Shakespeare are 6DB gain which is the generally recommended max gain for smaller boats. Too much gain can cause problems in rough seas due to the compressed transmission band.
You shouldn't have any problem while trailering with the antenna laid down. Probably less stress on it and the mount than if you running with it up in a big sea. Securing it lightly with a bungee will keep it from bouncing up & down.
Get a premium antenna, Shakesspeare 5225XP or Digital 529, they do perform better than the cheepies. Dave

seafari25 · #7 01-26-2009, 10:12 PM

My fathers old 21' Calais tunnel hull, which he purchased second hand, came with 2 VHF antennas. The one installed on the boat was a 4' steel which we replaced with an 8' whip which was laying in the cabin. i'm not sure what each db were however I do know that the 4 footer had a much greater range. We changed it because the 8 footer looked better but later realized that the original owner may have changed it due to the better range as he used the boat mostly for off shore purposes.

Also I seem to remember that antennas should be matched with the radio. I'm not sure if that is just for CB's and just with the older models or if this is even a factor today.

Rich · #8 01-26-2009, 10:34 PM

As stated above, most of the available antennas from Digital and Shakespear are as follows:

3' = 3dB
4' = 4dB
8' = 6dB

Digital does offer a line of 4' with 4.5 dB..

4' digital

bigeasy1 · #9 01-27-2009, 02:55 PM

Thanks to everyone, for the good info,looks like I'll be staying with the eight footer on the tower.

Fr. Frank · #10 01-28-2009, 12:01 AM

Go with a very good 8' antenna. You need to have one with a brass ferrule, mated to a brass or stainless mount. DOn't worry about having it lay out horizontal, it will be fine. Jus attach a bungie or tie-down from the cleat to the upper 1/3 of the antenna to keep it from oscillating through a big arc while trailering.