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Old 18-04-2021, 15:10   #1
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VHF antenna on mast

Does the VHF antenna need to stick out the top of the mast to work properly, or will it work if mounted further down as long as the antenna does not touch the mast (aside from mounting bracket).
My trailer sailor has the mast up and down constantly, and it would be nice if I didn't need to worry about adding extra height.
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Old 18-04-2021, 15:45   #2
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Re: VHF antenna on mast

You can mount the antenna on stern rail or deck & it will perform satisfactorily.Avoid mounting it anywhere "inboard" where it will be in the "cone" of the stays,as this area acts like a shield,partially blocking radio frequencies. Cheers/ Len
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Old 18-04-2021, 16:03   #3
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Re: VHF antenna on mast

Quote:
Originally Posted by BugzyCan View Post
Does the VHF antenna need to stick out the top of the mast to work properly, or will it work if mounted further down as long as the antenna does not touch the mast (aside from mounting bracket).
My trailer sailor has the mast up and down constantly, and it would be nice if I didn't need to worry about adding extra height.

Antennas work poorly when they are close, in the horizontal direction, to an aluminum mast. Close is less than about three feet, and it's usually not practical to get them further away than that on a trailer sailor. On a larger boat they can be mounted on the spreaders although this introduces its own complexities.


Have a look at the Shakespeare 5242-A. It has a removable whip that you can easily take off when your moving the boat on a trailer. The electrical portion of the assembly remains sealed when this is done so there's no need to cap it or cover it. It won't perform as well as a fiberglass antenna in the same spot, but height is king and you'll be better off than you would with a fiberglass antenna down low.


You can put the antenna down low somewhere as described upthread but it will cut your range in about half. Depends what you want to get out of your VHF.
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Old 18-04-2021, 17:37   #4
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Re: VHF antenna on mast

Quote:
Originally Posted by BugzyCan View Post
Does the VHF antenna need to stick out the top of the mast to work properly, or will it work if mounted further down as long as the antenna does not touch the mast (aside from mounting bracket).
My trailer sailor has the mast up and down constantly, and it would be nice if I didn't need to worry about adding extra height.
Any metal in close proximity in the same plane can and usually will both detune the resonant frequency of the antenna as well as alter it's impedance. How much effect is variable and you might not even notice the effect on reduced ERP unless you are on the fringe of reception range but why take the chance? Other options always exist on any boat.
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Old 19-04-2021, 09:05   #5
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Re: VHF antenna on mast

I just use my handheld most of the time. My main VHF antenna can be secured to a halyard on the mizzen in a couple of minutes if I need it.
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Old 19-04-2021, 16:29   #6
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Re: VHF antenna on mast

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Originally Posted by bailsout View Post
I just use my handheld most of the time. My main VHF antenna can be secured to a halyard on the mizzen in a couple of minutes if I need it.
Thatís very innovative. Well done.
The OP didnít state usage and being a trailer yacht your system would be perfect.
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Old 19-04-2021, 17:27   #7
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Re: VHF antenna on mast

Usage is, I want to be able to listen to VHF while sailing, and I am unable to do that currently because my antenna is on stern rail and the tiller pilot interferes with reception.

I see there are a number of folding antenna mounts that would do what I want. The idea of removing the antenna when I take down the mast, and putting it back on before I raise it, would likely mean I would forget to mount it.. I have that problem already with the wind indicator, but it is a good suggestion.
The spreaders on this boat are very light material, and I doubt they would be suitable for an antenna mount.
Not sure what is meant by "My main VHF antenna can be secured to a halyard on the mizzen in a couple of minutes if I need it", How do you keep it from flopping around while up there after you raise it?
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Old 19-04-2021, 18:18   #8
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Re: VHF antenna on mast

As VHF radios are for the most part line of sight the higher your antenna the more range you get however, long runs of coax will also have loss of performance so donít cut corners on coax cable. Use high quality heavy cable.
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Old 20-04-2021, 12:13   #9
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Re: VHF antenna on mast

Height of antenna is important for VHF. Distance to horizon in nm is 1.17 x sqrt(height in feet).

height --- distance to horizon

5' ---- 2.4nm
10' -- 3.4nm
15'--- 4.5nm
20'--- 5.2nm

Of course you also can add distance to horizon at antenna of the station you are talking with. But if you intend to speak with other small boats, your antenna should be high.

I don't see how it would be a good solution to string up the antenna from a halyard. Lots of motion will soon break the coaxial center conductor.

Seems to me a spreader mount is best for your usage. What would be the problem with that?

Why does autopilot on tiller interfere with VHF? Electrical noise?
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Old 20-04-2021, 13:10   #10
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Re: VHF antenna on mast

What about an old wood mast? If you mount an antenna on a spreader like the last contributor suggested would the mast still be an interference?
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Old 20-04-2021, 18:15   #11
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Re: VHF antenna on mast

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Originally Posted by waterman46 View Post
Seems to me a spreader mount is best for your usage. What would be the problem with that?

The OP has a 26' trailer sailor. Spreader tips are particularly vulnerable and difficult to protect when moving the boat with the mast down.


Quote:
Originally Posted by Lemsteraak View Post
What about an old wood mast? If you mount an antenna on a spreader like the last contributor suggested would the mast still be an interference?

Generally, wood masts are transparent to VHF, that is, they have little effect on the pattern.
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