what size is best for vhf antenna ?

zodiac 4.2 · 10 August 2013, 19:44

Hey guys, i am just wondering what most people use for vhf antennas on there ribs. I would like strong signal but not sure i want to use a 8ft fiberglass antenna?

mick · 10 August 2013, 19:56

I got 2 of these 1 for VHF Tother for AIS work fine for me http://www.saltyjohn.co.uk/boat-products-antennas.htm

zodiac 4.2 · 10 August 2013, 20:06

Thank you for the recommendation I am going to look into them. I was not sure if a 3db was strong enough

ShinyShoe · 10 August 2013, 20:07

What radio are you using?
Do you have an A frame?
Who are you talking to? And where are their aerials?

zodiac 4.2 · 10 August 2013, 20:17

I just picked up a standard horizon gx1600 25 watt vhf marine radio. Just installing it on my zodiac. Wanted it for weather updates, marina Communications stuff like that.

ShinyShoe · 10 August 2013, 20:32

Weather Updates
The radio won't make any real difference. Antena might, but I'd expect unless you are at the limits of reception their antena is probably chucking out far more power than you need to receive. I'd expect to get it on a hand held antena so should be no issue whatever aerial you choose. They don't need to hear you.

Marinas
You probably aren't much more that 5 miles away when you want to talk to a Marina? So again handheld will work so any antena should. Bear in mind the marina could be on handheld depending on the size of the marina!
Some marinas will have land obstructions quite close - so maybe a better antena will help. 25W will help too. However, height is what usually makes the biggest difference both for height and for avoiding local obstructions like yourself. Hence the A Frame question.

Beware some antena are sold for yacht masts which can be leaning up to 30degrees when underway. You wont be.

A helix on top of an A frame might not be much worse / even better than a straight aerial with its tip finishing at the same height.

A helix on the side of the console wont be as good - less height, and more risk of accidental obstruction by people etc. But could still be suitable for what you want...

Do you know how far you'd be from a CG mast?

zodiac 4.2 · 10 August 2013, 20:46

Thank you very much for the great info i do not know much at all about vhf but you cleared up alot of my questions. As for the a frame question i am not sure what that is but i think it maybe the bar at the back of the boat then yes i have one

I am also not sure about the cg mast location.

ShinyShoe · 10 August 2013, 21:12

A Frame is tha Metal Frame over the engine. It gives you a "higher" point to attach things. Beware that if you put a tall aerial (like the METZ) on there then you may have height issues if you are storing in a garage or on some UK slipways there is a barrier like you get at the entrance to some car parks to keep trucks etc out.

I'd think the Metz on the A Frame is the best you'll get. But a helix on there might not be too wicked a combination either.

zodiac 4.2 · 10 August 2013, 21:17

Yeah i am thinking that's the route i am going to take. I keep boat on a marine railway in a covered boathouse so i may have to use a hinge mount type setup so i can just fold it down. Thanks again very helpful

Peter_C · 11 August 2013, 09:56

We boat in fairly remote locations and I want access to the Coast Guards Rescue 21 as much as possible, so a 8ft antenna was the answer. I do not have a tower and do not want one as it would get in the way of my launching wheels and add unnecessary weight. I used fairly long screws and put it directly onto the transom and haven't had any issues. The nice thing is it folds right down to the floor of the boat, using a folding antenna mount.

zodiac 4.2 · 11 August 2013, 12:45

Thanks for your input, it does come down to what the vhf is used for, I have learned that something like a 8ft is about 6db witch goes a long way. I think you have the right application for your needs. Nice pic!

whisper · 11 August 2013, 12:51

With VHF arial's it's the higher the better

Pikey Dave · 11 August 2013, 16:20

Quote:

Originally Posted by zodiac 4.2

Thanks for your input, it does come down to what the vhf is used for, I have learned that something like a 8ft is about 6db witch goes a long way. I think you have the right application for your needs. Nice pic!

AFAIK (& I might be talking complete b0110cks) the higher the db gain the more directional the signal, in that a high DB antenna "flattens" the radiation pattern from a doughnut to a disc. If the boat is low & rocking, this has the effect of directing the signal into the sea at one side & up into the air on the opposite side. High DB antenna might not be the answer in a low boat as you will only get line of sight anyway. Like I said this might be a load of rubbish, I'm sure someone will be along to clarify.

Mollers · 11 August 2013, 16:36

As I've often mentioned, I binned my useless Rib Raider for a 1.2m GRP and the VHF lit up with radio traffic. Never heard a squeak with the Toys R Us black spring.

zodiac 4.2 · 11 August 2013, 16:44

I may use a tv tower off a house lol nice 50ft of powera

whisper · 11 August 2013, 17:03

When I did my VHF course there was a slide on how efficient aerials were, there are calculations you can do to see how much performance/range you would get from different setups.

But how much just a few feet will make I couldn't tell you but maybe someone else can

I have the rib raider, looks good but I don't rate it. Landlord has the right idea on his all black & grey rib, no nonsense and great performance

zodiac 4.2 · 12 August 2013, 04:05

now that's a sweet looking rig!

9D280 · 12 August 2013, 15:18

I have both a 1.2m whip & a raider. (Long story involving a low door....)

Personally not noticed a real difference between them on the Clyde / West coast, and I think (open to correction here - there was a thread on the subject way back in the day) that the MK1 Raider was a pile of poo in the durability dept, whereas the MK2 I have was bounced off the garage door about 5 times in the early days (part 1 of the "why I have 2 antenna" story......

) - It still transmits & receives fine.

The thing that's more likely to kill your comms is dodgy connections on the cables.....

Salty John · 12 August 2013, 16:35

To go back to the OP's question, the best antenna configuration for a RIB is, in my opinion, a 3dbi whip antenna on a pole. This gives the right combination of a broad radiation pattern and height. You want height to get a better look at the horizon and you want a broader radiation pattern so that more of the signal is pointing at the horizon at any one time.
Someone earlier explained how on a boat you need the broader radiation pattern that comes from a lower gain antenna because a more focused pattern needs a steady base so it can point at the horizon. Boats are never still.
An 8' fishing rod type antenna gives the benefit of height (actually 4', the radiation pattern centre is halfway up the antenna), but you lose out to the too focused high gain pattern. A whip on a pole gives the best of both worlds.

zodiac 4.2 · 12 August 2013, 20:03

Thank you for the info, Lots more to it then i could have dreamed of, happy i asked!