rail-mount vhf antenna

[Gunfleet]

Every time something goes wrong with my vhf it's the antenna or lead thereto, not the radio itself. I suppose running a cable in a salty environment up an aluminium mast and connecting to the business end of the antenna (which is what most of us effectively do) is asking for trouble sooner or later. As a back up I have decided to fit a rail mount antenna on the push pit. But which? Anyone done it? Any success? No I know you can't use a rail mount antenna to talk to your chum in the next river, but even in flat Essex the Coast Guard antennas are high and communication with them will work, which is the important bit with a back up. By the way, the spelling function on this YBW software doesn't like me writing aluminium. Listen, Americans... it's the Queen's English.

 

[Channel Ribs]

I am doing likewise at the moment to Cottontail and using a rubber ducky type which is intended for the RIB market - easy to fit and should not get in the way.

As you rightly point out, not as good as a mast head but it will allow you to use the full 25W of your fixed radio.

Edit: A link

 

[Talbot]

I dont want to rain on your parade, but I rigged one of those vtronic helical aerials to my pushpit as the aerial for my AIS. The resultant range achieved was so good, that I threw it away and got a 1m steel whip from jgtech instead, and achieved double the range. Thats not that surprising as you would expect at least a 3db reduction in signal strength using the dumpy aerial.

My recomendation, put the aerial back at the top of the mast to achieve a decent range for your emergency transmitter. use a 1m steel whip on the pulpit as a secondary aerial only (and for AIS signals.

 

[Salty John]

A quick release rail bracket and good quality whip with an appropriate length of cable is a good idea anyway in case you ever lose the rig.

 

[Malcb]

Just over a week ago I got a loud and clear conversation between another boat whose position was known to me. We were just over 12 miles apart. Both our aerials were at the top of the mast. Could you do that with one on the pushpit. Don't think so. If I'm standing up with my handheld the aerial is higher. You ned the aerial as high as you can get it.

 

[Gunfleet]

My handheld puts out 5W max with (I've no doubt) no gain. The Navico VHF I have puts out 25W @ 3Db with a simple antenna. As I said in the first post, I don't want to talk to my chum in the next river, I want to be able to talk to the coastguard if all else fails.

 

[SvenglishTommy]

I have one of those 6db white plastic ones as a backup that can easily be set up in the pushpit in case of dismasting or loosing the mast top one. If you're having trouble with your mast top one, why not fit a really good one (like js48s Metz, absolutely fantastic reception) and plumb it in with good soldered connectors on RG213 cable.

 

[Robin2]

I mounted a Vtronix helical antenna as high as I could reach on my backstay and it works fine for AIS reception. I can easily switch it to my vhf if needs be. Its much higher than if it was on the pushpit - and out of harms way. I mounted it to a small piece of flat stainless steel fixed to the backstay with the U bolts from 2 bulldog clips.

 

[wooslehunter]

Problem with being on the backstay is that if the mast holding you main antenna falls down, the backstay holding the emergency one will also have fallen down.

The best you can do is to mount a normal antenna on the pushpit. You could always mount it on a short 2m mast if you want to get it a bit higher. This will be better than a rubber duck.

 

[William_H]

I use a home made antenna on the pushpit as the main antenna and would say it works very well. Certainly I can talk to our sea rescue group 4kms away through a very high hill no trouble.

The antenna style is called a coaxial antenna. It consists of 17.5 inches of braid removed from the end of a piece of coax long enought o reach the radio. The exposed centre conductor becomes the antenna. The ground plane is a 17.5 inch section of braid removed from the large RG8 type coax. It is soldered to the end of the braid and fitted over the main coax to form a second outside braid. The braid is trimmed to 17.5 inches when fixed in place by tape on the outside.
This antenna is fitted into a piece of plastic conduit type tubing about 15mm iside diameter which is mounted to the pushpit with hose clips or similar.
The plastic tube/mast is as long as you want(mine is about 1.5 metres) but preferably with all the extra outer braid above the metal of the rail. To reduce windage and have a shorter tube pole I actually have about 15cms of the inner antenna wire sticking out of the top of the tube unsupported. Obviosly you need sealer at the top of the tube. The VSWR of the antenna is quite good across the band. and not being a high gain antenna means it is good at large heel angles. The only join in the antenna/cable is at the radio coax antenna so it is reliable. DIY is good. olewill

 

[whipper_snapper]

[ QUOTE ]
Problem with being on the backstay is that if the mast holding you main antenna falls down, the backstay holding the emergency one will also have fallen down.

The best you can do is to mount a normal antenna on the pushpit. You could always mount it on a short 2m mast if you want to get it a bit higher. This will be better than a rubber duck.

[/ QUOTE ]

I think the best you can do is to keep a spare, on its length of cable, safely in a box below. That gives you all options. If the mast is still there you can hoist the spare up easily enough. Otherwise you can attach it to whatever remains. If the mast comes down, there is a fair chance it will take out an antenna on the pushpit as it goes.