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 CB / VHF question

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Posts : 58
Join date : 2013-10-15
Location : Aberdeenshire

PostSubject: CB / VHF question   Tue Jul 07, 2015 5:39 pm

Are there any radio boffins out there who could answer this question for me?

I currently have a CB aerial and VHF aerial fixed to my roof rack. I would like to remove the roof rack and was thinking about fixing them to the top bar of the bull bar/winch bar. I would prefer to keep them off the roof.

Will I notice any significant loss in performance putting them in a lower position and on the very front of the vehicle?

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Posts : 582
Join date : 2012-09-28
Location : Milton Keynes

PostSubject: Re: CB / VHF question   Tue Jul 07, 2015 6:05 pm

The front bull bar is a common location for antenna to be mounted. It will affect your reception/transmission in an arc to the rear as both CB and VHF are line-of-sight. Another factor is that moving the antenna closer to the engine will increase interference somewhat from the electrical/magnetic fields generated by a running engine. Bull bar mounts tend to work best with HF radios which primarily use a signal bounced off the ionosphere...so signal goes straight up and back down...no issues with line of sight.

A mounting on the rim of the roof, or at the back of the roof (with full length of antenna above the roof line) might work better.

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Tom Mc

Posts : 3781
Join date : 2010-12-10
Location : Sant Boi de Lluçanès, Catalunya, Spain

PostSubject: Re: CB / VHF question   Thu Jul 09, 2015 6:22 am

What he said! scratch

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Terrain Expert
Terrain Expert

Posts : 1227
Join date : 2010-12-27

PostSubject: Re: CB / VHF question   Thu Jul 09, 2015 12:41 pm

It all comes down to "ground plane" which is basically the earth, which is the vehicle body which dictates the direction of the signal.

Ideally you want the aerial in the middle of the roof as the signal will radiate equally backwards and forwards and less to each side as there is less metal (ground plane) from the middle of the roof to the side of the vehicle, mount the aerial on the bull bar and most of the signal will radiate rearwards as most of the metal (ground plane) is behind the bull bar.

In reality for CB it makes little difference to an off roader as most transmissions are in relatively close proximity so anyone in front will get a weaker signal, but usually be close enough to receive a good signal and transmission.
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