VHF Aerial setup question for you teckie types

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If I change the aerial on my boat (fixed VHF) wont I need to adjust the SWR?

How? Should I buy a cheap SWR Meter?

I know a bit about this from my early basic electronics training, but only practical experience was setting up 27 MHz AM CB's years ago. I assume similar applies to marine VHF

Thanks

D
 
A 27Mhz SWR meter will not give an accurate reading at VHF which is a much higher frequency.
You really need an amateur 2 meter (144 Mhz) type which will be OK.
They can be had relatively cheaply from somewhere like Waters and Stanton.
Generally speaking though if you are just replacing the antenna with another pre-tuned marine type then it will probably be OK, as long as the grounding is good.
Always a good idea to check it, but I wonder actually how many people do??

Steve
 
Nothing to adjust on a boat aerial but the cheap CB/VHF style VSWR meter will certainly tell you that the power is going up the wire.
I used one the other week and it showed up a slightly corroded connector. The VSWR read was better than 1.1 to 1 with a good connection and 1.3 to 1 with a slightly dodgy plug (braid soldering not too good)
 
No,

VSWR normally not measured. It is just used as a check in the event of a suspected aerial malfunction.

VHF is at a higher frequency than your CB rig and a quarter wavelength as VHF will be aprox one fifth that at 27mHz.

In other words you have to mount a VHF aerial five times nearer to an obstruction then a CB one for the same mismatch.



Thus it is easier to mount a VHF aerial nearer to free space


They are normally preset by the manufacturers to an acceptable match and have no adjustment.

I don't know if my explanation is explicit enough.


(I am saying this but I have a VSWR meter mounted above my chart table, normally for my HAM SSB but I have the facility to route the VHF signal through it.)

Iain
 
Thanks Steve,

I dont have any of the CB stuff now anyway, I used to set them up years ago when they first appeared.

But the advice on here confirms its not so critical at the marine wavelength
 
you cant adjust the swr on a marine vhf system. the aerial is tuned to give a low swr at the marine frequencies at the factoryso all you do is plug it in.
 
Thanks Birdseye,

I had a look at the aerial and noticed it was not adjustable.

There is a crack int he plastic base so I was thinking of getting a replacement.

Cheers

D
 
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