Poor radio reception and erratic radio behaviour

[Winchweight]

Ok, two questions about two radios in different vehicles:

Q1. The radio in the van used to work fine with a wing mounted aerial, but after a major bodywork refurb, the garage refitted the aerial on our light bar (its a Syncro). The light bar is mounted to the fibre glass tub on the roof of the cab and doesn't make contact with the metal work. As a result the reception is bloomin' awful - that also goes for the CB aerial which was moved alongside at the same time.. Can I earth the light bar (I tried running a wire down from a bolt to the main van body: no difference) and fix both, or do they need moving?

Q2. Different van. I have fitted a couple of different radios and the problem appears on them all. When connected via the DIN connectors (installed by previous owner), everything works fine. Except the radio switches itself on periodically until eventually the battery dies. From what I can see, all appears correct on the DIN fitment, but clearly something isn't. So, what is the likely cause, is there a common mistake made and how do I find the fault and fix it please?

[clift_d]

Your first problem sounds like a ground plane issue:
http://www.thunderpole.co.uk/cb-radio-g ... plane.html" onclick="window.open(this.href);return false;

[Mocki]

short sharpe answer to the antenna problems

it wont ever work any sense where it is .
there are steps you can take to improve it, but none will compensate for no metal


a little back ground info:
the bit of your antenna that is sticking up is only half the antenna , the other half is the metal it should be bolted to , so you are missing the lower half of the dipole.
this isnt such an issue the higher the frequsncy you are using , because the electrical length of the antenna is smaller, there fore less "groundplane" is needed to make up the lower half of the antenna .... broadcast radio is typically 75cm in electrical length, where as the CB is 2800cm (approx) so you see, whilst the physical length maybe only 120cm the electrical length is much more. basically you need the same "groundplane" as radiating element

[Winchweight]

Ahh, thank you. Guess I need to move them then.

I assume I can't get around them by running wires to the body?

[Mocki]

You can, and by all means try , but it is a compromise ....
If you must try, use the thickest earth strap you can get away with and keep it symmetrically equal as much as possible across the vehicle width ( don't just put one earth point onto one extreme side basically)

[Winchweight]

Thanks Steve, advice much appreciated.

[Oldiebut goodie]

It's a lot easier in a boat - you have one heck of a large ground plane!