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Discussion Starter · #1 ·
Hi all, I know this has been covered in some depth before on here but I just wanted to confirm I have the right piece of kit before ordering!

I have an Icom IC-M411 Unit and need an antenna to use with it. Will be used on my small 4.5m open boat out of Ilfracombe Harbour - North Devon. This is the unit that a few people on here seem to like and what I was thinking of using. Will this be about right or overkill on such a small boat? I used to have a stainless whip type antenna which I never needed to use but never heard anything either apart from my mate 20m away in the harbour, which is why I think I need an upgrade.

My Boat:



The Antenna I was thinking of using:

http://www.force4.co.uk/3555/Glomex...tenna-with-Stainless-Steel-Ratchet-Mount.html

Cheers

Ste :)
 

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I would prefer to have the anttena mounted on the "A" frame on the stern, better seperation from my head and less prone to placing a hand on it and suffering potential RF burn.
The antenna your thinking of would do the job well however have you tried to find out why the one you have is not performing? usually a good anttena the base loaded type.
 

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Discussion Starter · #3 ·
Thanks, wasn't aware they were dangerous being close to your head and what is RF Burn? The A frame on the back isn't that strong being single tube and only has a small mounting plate at the base. Saying that, could mound it on the back of the boat where the A frame bolts on. Would lose a little height say 70cm or so. If it really needs to go on the Rear A frame, could get some flanges made to strengthen the base although what extra gain would there be from it being 70cm higher


Cheers

Ste. :)
 

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as i am a radio ham also the bigger the antenna the better more gain further distance depending how far out you go ?
i use 2.5mtr ants on mine gives me 50plus miles
there is a vswr meter you can use to test the ant via radio so if you find some one who has one worth making shure it works as i know alot who have soldered the pl259 plug on the end of the coax and 1 strand from the braid to inner core makes a dead short rendering it usless
hope this help's :sad2:
 

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A 2.4 metre aerial mounted on the transom will be plenty high enough for an inshore boat. No need to over-complicate matters! However, as the OP says, check your existing set-up because it should work anyway.
 

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Discussion Starter · #6 ·
Well, won't be going too far out as its not a huge boat, mainly up and down the coast although have it for emergency use really and in that case, would need to reach the coast guard at swansea I assume, which isn't close!! Don't think I know of anyone with one of those but will def. test if I do find someone who has one.

Salar, This is the one I have now a 1m whip style navman antenna which works across the harbour but not hearing anything further away. Have a feeling this is designed to go on the top of a mast maybe?



Thanks

Ste :)
 

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A hand held with a relatively tiny antenna would perform better than you describe - hence the suggestions you get the existing set up checked out first. The antenna you already have, when everything is working OK, should be good enough, although there will always be room for improvement so you still might want go ahead with your new purchase anyway, but if you trace the fault, I'd be inclined to put the cost of a new antenna towards a waterproof hand held to use as a back up instead.
 

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Hi, not wanting to worry you, but the North Devon coast is a bit sketchy for good coastguard coverage...lots of little nooks and crannies and Swansea CG's remote sites are a bit...remote!
A 1m stainless whip antenna should work perfectly well with your Icom and give you about 20 miles range. Dont worry about RF burns, on 25 watts, it'll never happen.
On a RIB, the stainless antennas are a good idea as they are more robust. Get a good make like a Vtronix or Shakespeare, about £40. Go for one with the cable moulded into the bottom of the antenna, not pushed into or plugged in at the base. less to go wrong. Vtronix MD20 is a good option.
Once fitted, use your DSC to call Swansea CG and ask for a radio check. They will be pleased to help you out.
Regards Tony
 

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Your whip aerial should be fine. I would imagine there probably is a fault at the plug on the coax. It only takes a single strand of the outer shield to touch the inner core of the cable to cause problems. The best bet is to cut off the plug, strip the cable back and fit a new one. Solder the tip of the plug and you should be fine.
 

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It's worth replacing your coax salt water and the elements play havoc with it and water inbetween the braids with salt will corrode it.

Low loss coax with the brown insert pl-259 is your best bet and make sure your antenna system has a good ground,Clean the contacts up etc.

25w should get you at least 40-50 miles range without any problems with your existing antenna if not further.
 

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Dont be tempted into getting too big an ariel.
Longer will give you more range but will be much more affected by the boats angle. Shorter ariels have a greater Vertical Angle of Transmission. This is important on small boats that rock and roll the most. It is why Inshore Life Boats have short (1 - 2 meter)ariels. I would go for 1.5 meter.
Buy one that is too long and you will hear everything from miles around but your transmissions will sound broken when things get choppy.
Put the ariel as high as possible or even on a short pole.
Mount it as vertical as possible, a rakish angle looks great but works badly.
 

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What's the difference between a 1.5 metre antenna on a 1 metre pole and a 2.5 metre antenna ?
Lots,
One gives height of ariel generaly gives more "line of sight" range.
Length of ariel narrows the angle of transmission. Although ariels transmit in a 360 degree arc all around, imagine that at any one point it is like the beam from a torch projecting at 90 degrees to the angle of the ariel. A long ariel has a narrow "beam" but great penetration. A short ariel has a wide "beam" but less penetration, however, your signal will continue to reach the target even though you rock about.

Its why yachts tend to put a short ariel at the top of the mast.
 

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Before you buy a new antenna I would get your hands on a SWR meter & check out your set. It could well be something very simple. A knackered antenna will ruin your transmission but you should still recieve ok (a bent coat hanger will recieve fine but will be no good for transmission). Normally with an antenna problem (such as a duff PLL plug) you will recieve fine but no one will be able to hear you.
Get the meter (if you can"t borrow one) from a CB place (much cheaper than a chandlers) just make sure you tell them it is for marine VHF.
I paid £25 for my meter from a CB shop & it is a very handy piece of kit to have.

headlight
 

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I have a 5' Glomex which works fine on my 18' boat. I know Cascars has the bigger one and he gets to the moon and back (mind you, he does go a fair way off shore)! I am currently in the process of raising this by 12" as I am fitting it onto a S/S arch (on top of the cabin) which in theory should give further field. A 2.4m on an 18' boat is pretty big in my opinion but as has been suggested by others, depends on your choice as to how far you want to transmit v obtaining a suitable match that is also pleasing to the eye. My spare set has a 1m whip and is pretty naff although this too may improve as it too is going on the arch.

Regards

Harry
 

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On my 18ft Raider I have a Silva S10 & a Silva S15 VHF. The S10 has a 1m Glomex stainless whip & the S15 a 1.5m Glomex +6db fibreglass antenna. Both are mounted directly on the roof (6ft 6" above the deck). There dosen"t seem to be much difference transmit & receive wise between either (possibly the S15 set up is slightly better).
I bought the SWR meter because I was having problems with the S10 which is why I got the S15 & second antenna (could hear boats from miles away but they couldn"t hear me). The meter showed that my transmission was poor & this was sorted out by cutting the PLL plug off & re-attaching.

headlight
 

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BTW the chandlers told me that the output stage of my VHF was knackered & that there was no way of repairing it & I needed a new set.
I went to a CB shop who said that if the output stage was knackered of course it could be repaired but without looking at it they couldn"t say whether it would be worth it cost wise or not.
They suggested the SWR meter & the repair took me 2 minutes & a bit of solder.
Glad I didn"t listen to the "swindlers" sorry chandlers.
I then got the second set as a back up. If I had listened to the chandlers I would have binned the first set.

headlight
 

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Steve,

This might raise a few eyebrows. As your thread relates to the output and size of VHF antenna's, it may be worth considering just how small the new AIS antenna is. I just bought one (£40+) and it is about 9" tall and flexi rubber. I decided to buy a dedicated AIS antenna because I am updated a few instruments anyway. I just hope it works ok.

Regards

Harry
 

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Discussion Starter · #20 ·
Cool, thanks for all the advice guys! Will keep hold of the antenna I have then for now and check out the connections in the first instance and re solder new plugs and cable and failing that, will ask around and get hold of a meter. The antenna will be mounted 6' above the deck/water.


Cheers

Ste :)
 
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