Sony DAB radio drops signal when 12V socket in use

[rnem_uk]

Hi All....

I've got an issue with DAB radio in my 13 Plate Focus...   when I plug in my phone to charge it, DAB signal drops to near nothing and I have to revert to FM.  Ford 'reset' the system, upgraded the software, and replaced the head unit, but until today, I didn't realise that my USB adapter drawing power had anything to do with it....

I have an Aukey 2,4v dual usb adapter, and a 20 awg 3m cable running to my phone; which is positioned to the right of the steering wheel.  The cable runs under along the edge under the steering wheel and up by the side of the door.

I find it hard to believe that the adapter is the cause of the problem, since it's not a knock off from a well known auction site.  Since I'm charging an LG G3, it's drawing a lot of power.  Could this be an issue? 

I have a couple of 'cheap' usb adapters, but they don't give out enough power to charge the phone while it's on in satnav mode, hence spending a bit more on something that will still charge the phone when it's running.

Advice appreciated....

[Micro]

May be a faulty noise suppression capacitor inside the charger or just poor design, putting the switching noise back into the grounding system. The long wire may also be acting as an antenna for the noise... where is the DAB antenna wire running?

When you say 20awg 3m cable, do you mean USB cable? Is the charger in the cig socket?

There are cheap 5v 3A dc-dc converters that are used for powering dash cams - i've never had an issue with radio or GPS signal strength in my own vehicle (nor from my Brodit active charger).

[rnem_uk]

Yes, it's a high quality USB cable to reduce power loss along the length. 

I've got no idea where the DAB wire runs.  It's wherever Ford put it.  I'll try a 'cheap' microusb charger to see if that works, but I know for sure it isn't long enough, nor will it charge my phone. I havre two of the aukey adapters (one for other car), so I'll try the other one too.

[rnem_uk]

I've tried two aukey usb adapters, 3 griffin ones (not sure how genuine they are as bought from an auction site) and a different cable.  None make a difference.  It's as if a power draw greater than x amps on the 12v socket causes DAB to lose signal.  IMHO, that's a serious design flaw.