VHF antennae on a kayak mounted pole ?

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charleston14
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VHF antennae on a kayak mounted pole ?

Post by charleston14 » Sun Oct 07, 2018 10:14 pm

I’ve never seen one and so there’s probably a reason why but has anyone ever thought of increasing the range of a handheld marine vhf by having the antenna higher up?

E.g a boat mounted antenna ? ( For plugging in to in an emergency) In theory it should be possible to disconnect the short whip antenna and connect to a cable with an antenna at the top of a pole, eg at the top of a kayak sailing mast or similar extended device

Logic being that the higher up the antenna the better right ?

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Re: VHF antennae on a kayak mounted pole ?

Post by Chris Bolton » Sun Oct 07, 2018 10:20 pm

I've thought about it but never tried it. Possible problems are the difficulty of rolling with a mast up, so it would have to fold down, plus making electrical connections in the marine environment; it all gets a bit complicated! It's also worth considering what the limiting factor in VHF range is - is it the line of sight horizon or is it the power of a handheld transmitter? I don't know, but in most cases I'm either calling or listening to a Coastguard antenna mounted well above sea level, or (occasionally) another kayak within visual range.

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Re: VHF antennae on a kayak mounted pole ?

Post by andynormancx » Sun Oct 07, 2018 10:36 pm

The limiting factor is not the power of the transmitter. The limiting factors are line of sight and the antenna design.

With the right antenna and line of sight (i.e. both transmitter and receiver on top of big hill/mountain) a 5W handheld VHF radio can be heard 100 miles away or more.

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Re: VHF antennae on a kayak mounted pole ?

Post by andynormancx » Sun Oct 07, 2018 10:43 pm

But as you noted, raising the antenna a few feet when talking to the coast guard may well make little difference.

Say the radio is normally about 1 metre above sea level when you are in a kayak and the coast guard antenna is 50 metres ASL.

The radio horizon for the combined setup is 33km. Even if you raise the kayak antenna to 3 metres, the combined radio horizon only goes up to 36km.

All of that assumes flat ground/water between the kayak and the coast guard though. If your line of sight was blocked by relatively low stuff close to the kayak then you'd get more benefit.

http://www.vwlowen.co.uk/java/horizon.htm

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Re: VHF antennae on a kayak mounted pole ?

Post by PlymouthDamo » Sun Oct 07, 2018 11:38 pm

I wouldn't want a tall mast on my kayak as it would get damaged eventually. Would it be possible to keep a coil of antenna wire on you which you could screw into your VHF in place of the stumpy antenna when needed? Then you'd somehow fix the other end to your main paddle blade and hold it up, or fix it to the blade of your spare paddle which you'd slip down the back of your BA so it's permanently sticking up? Dragon's den anyone?

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Re: VHF antennae on a kayak mounted pole ?

Post by charleston14 » Mon Oct 08, 2018 5:26 pm

pop up kayak sailing mast with antenna on the top ..or an extending pole that engages into a fitting on the deck and secured by bungees.

Holding up a paddle might work, but attaching it to a paddler is perhaps a bit risky.

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Re: VHF antennae on a kayak mounted pole ?

Post by PeterG » Wed Oct 10, 2018 9:55 am

Handheld VHF can be very quirky, near the cliffs in Scotland sometimes someone 50m away in plain sight is out of range. On the other hand from the top of Butser Hill 270m you can hear the port traffic at Cherbourg 110 miles away. The handhelds have an aerial designed for all round use and not too affected by not being vertical. An aerial on a pole might be badly affected by our swaying on the sea.

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Re: VHF antennae on a kayak mounted pole ?

Post by mcgruff » Wed Jan 16, 2019 8:38 pm

Drone & relay?

Would be limited to reasonably calm weather though.

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Re: VHF antennae on a kayak mounted pole ?

Post by andynormancx » Thu Jan 17, 2019 10:41 am

I know it wasn’t a serious suggestion, but I suspect running 5 watt or greater transmitter on top of a drone isn’t going to do great things for the drones GPS receiver and compasses ;)

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Re: VHF antennae on a kayak mounted pole ?

Post by mcgruff » Thu Jan 17, 2019 7:42 pm

Actually it was serious in a brainstorming kind of way :)

I found this: https://www.youtube.com/watch?v=JwVcJAbqCmY


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Re: VHF antennae on a kayak mounted pole ?

Post by andynormancx » Thu Jan 17, 2019 8:28 pm

Even a brief shot of the screen showing he was managing to operate the drone in GPS mode successfully.

I’ll admit I was imagining a radio taped to the top of my Mavic, rather than the radio suspended some distance away from the body ;)

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Re: VHF antennae on a kayak mounted pole ?

Post by mcgruff » Thu Jan 17, 2019 9:00 pm

Probably not a terribly practical solution though :)

Still, if you had a medical emergency camped on a remote island and can't find anyone in range it just might help.

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Re: VHF antennae on a kayak mounted pole ?

Post by andynormancx » Thu Jan 17, 2019 11:00 pm

I think I’ll take my PLB rather than my drone. Especially as if my VHF is dangling from my drone it is going to be rather hard to use it ;)

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Re: VHF antennae on a kayak mounted pole ?

Post by seawolf856 » Fri Jan 18, 2019 1:36 pm

Well I thought that was a great piece of ingenuity and a well put together film. Editing the film to show the radio conversation from both ends and filming his drone with another drone was very well thought out, he basically took a lot of trouble to try something which is practically useless BUT which could lead to others having 'lightbulb' moments. The guy clearly emphasised this was not to be taken too seriously but it does show what can be achieved if you are brave enough and clever enough to think a little outside of the box. Hats off to him.

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Re: VHF antennae on a kayak mounted pole ?

Post by andynormancx » Fri Jan 18, 2019 1:52 pm

I've watched his videos before and he always puts a lot of effort in.

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Re: VHF antennae on a kayak mounted pole ?

Post by stewh » Wed Mar 13, 2019 6:22 pm

You can't just remove the hand-held's antenna and mount it higher. It won't work without a ground plane. Attached to the radio the body of the radio itself and capacitive coupling to one's body acts as a ground plane. A VHF marine band antenna is usually a half -wave antenna with built-in matching for end-feeding, or off-centre fed. The biggest problem would be preventing salt water ingress to the connectors.
The rubber duck antenna usually supplied with the radio isn't very efficient, but one can buy a telescoping antenna which is longer when deployed, and much more efficient, or a flexible 1/4 wave antenna that again is longer and more efficient. A 1/4 wavelength of insulated wire connected to the metal body of the radio, and allowed to hang down will also improve the efficiency of the radio/antenna system.

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Re: VHF antennae on a kayak mounted pole ?

Post by pathbrae » Wed Mar 13, 2019 10:27 pm

or a flexible 1/4 wave antenna that again is longer and more efficient. A 1/4 wavelength of insulated wire connected to the metal body of the radio, and allowed to hang down will also improve the efficiency of the radio/antenna system.
Interesting idea.

To save my tired old brain from doing the maths, what length of wire would be required for 1/4 wave on Marine Band VHF?
So much sea - so little time to see it.

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Re: VHF antennae on a kayak mounted pole ?

Post by andynormancx » Thu Mar 14, 2019 9:01 am

About 50cm

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Re: VHF antennae on a kayak mounted pole ?

Post by Sheepskin » Thu Apr 04, 2019 6:53 am

Something akin to this ? Though this is for non VHF so may not work but similar problem for wilderness fire fighters https://images.app.goo.gl/9bjAX3dfS5cA5Z2i8

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Re: VHF antennae on a kayak mounted pole ?

Post by andynormancx » Thu Apr 04, 2019 8:55 am

Exactly like that, that is designed for the same ranges that marine VHF uses. At a 45cm length it is centred on 166.5 MHz.

The problems are:

- it won't fit many handheld marine VHFs
- it won't be waterproof
- it won't help if you don't have line of sight to the whoever you are trying to talk to

I guess it could be useful in the case where you can land and get to higher ground to call for help and you've kept a 1/4 wave antenna in your boat.

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