Furo's Jimny Build

Are you using correct coaxial cable and a spliter box for radio

i use this cable
www.thunderpole.co.uk/cable/rg213-bx-coaxial-cable-black.html
I have dab radio with different aerial
are you using something like this
www.rightchannelradios.com/products/cb-am-fm-antenna-splitter

Thanks Jack! Yes I'm using a similar splitter and I bought that exact coaxial cable. A coaxial cable runs from the radio to the splitter, then another coaxial cable runs from the splitter up to the radio mount on the roof (which has a built-in ground). I had hoped to attached the antenna directly to the original radio mount but it didn't fit, so I got another coaxial cable and joined the radio mount to a homemade antenna mount (just some washers and a M6 bolt that the antenna threads onto). So the whole length is coaxial cable apart from the join in the original radio mount.

So far I haven't been able to properly check it with anyone else who has a CB, but one thing that concerns me is there is absolutely no difference in my FM radio quality if I screw the antenna on vs leaving it as just the bolt! I don't know what that means.

furo wrote:

In this image you can see the bolt in the radio mount, to which I have attached a further length of coaxial cable. The cable runs to a bolt in the roof rack that I screw the antenna onto.

Sounds to me like you have made a direct short
between the centre core to the braid by going onto a bolt
they need to be separated by this kind of connector
www.thunderpole.co.uk/rf-plugs-connector...rg223-h155-type.html

this is the mount i use
www.thunderpole.co.uk/fixed-body-mounts/...stick-mount-kit.html

Thanks Jack. I was careful to fold back the braid and used heat-shrink over it, so I don't think it has shorted with the centre core.

If the whole thing is disconnected I only get static on my FM radio. If I connect the cable to the roof rack without an antenna I get reasonable signal. If I add the antenna the signal is unchanged. So is the whole roof rack acting as an aerial? Sorry if these are stupid questions. Do I need to make sure the antenna is isolated from the roofrack?