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  1. #1
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    Dab radio and charging phone interference

    Here is a strange one. Tuned into Absolute Radio on DAB and all is fine on driveway. As soon as I start charging my iPhone via the charging point in the armrest DAB signal is lost.

    If unplug the phone the signal returns. Obviously interference for some reason.

    Any ideas why?

    Thanks
    Current: 2013 S4 Avant, Ice Silver, SS heated seats, tech pack, AMI, B&O.
    Previous: 2011 Mercedes C350 CDI Saloon

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  3. #2
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    Quote Originally Posted by gr4z View Post
    Here is a strange one. Tuned into Absolute Radio on DAB and all is fine on driveway. As soon as I start charging my iPhone via the charging point in the armrest DAB signal is lost.

    If unplug the phone the signal returns. Obviously interference for some reason.

    Any ideas why?

    Thanks
    I Just googled this and it seems i'm not the only one with this issue.

    Perfect DAB signal when phone is not plugged in to 3rd party usb charger. As soon as i plug it in. Signal vanishes

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    Quote Originally Posted by discuit View Post
    I Just googled this and it seems i'm not the only one with this issue.

    Perfect DAB signal when phone is not plugged in to 3rd party usb charger. As soon as i plug it in. Signal vanishes
    It's weird. I do get a dab signal sometimes when charging the phone but the signal is very weak. It is lost often making playback experience very poor. Have to unplug phone.
    Current: 2013 S4 Avant, Ice Silver, SS heated seats, tech pack, AMI, B&O.
    Previous: 2011 Mercedes C350 CDI Saloon

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    As an update to this, I recently moved to another phone and bought another cigarette charger. Same thing happens. Soon as you plug this in the DAB radio signal drops. Unplug the charger and DAB reappears.

    I contacted the makers, Brodit and they claim they haven't heard of any other reports of interference. I can only assume there is a fault in the Audi wiring loom. I am about to send the plug charger back and replace it with a USB based one like I had before. Will report back any findings if anyone is interested.
    Current: 2013 S4 Avant, Ice Silver, SS heated seats, tech pack, AMI, B&O.
    Previous: 2011 Mercedes C350 CDI Saloon

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    Unlikely to be a wiring fault per se. More likely an overall design weakness giving unfavourable interaction between the Audi DAB antenna design and standard car charger design.

    I'm thinking rather than the charger outputting EMI or RF and actively interfering with the DAB signal or even causing dirty DC noise in the wire harness, when it's operating under load with a phone attached, it and the cable are more likely behaving like an active antenna and drawing some of whatever signal is available. The signal strength varies with weather too which might explain the times you do have a weak glitchy signal and other times none at all. The signal arrives at the window antenna after making it through the fuzzy ball of the EM field surrounding the car so some of that power is lost already. If some of the remaining power is being picked up by the charger / cable / phone array, then that doesn't leave an awful lot for the DAB decoder to process.

    DAB is a fairly weak signal at the best of times and the quarter window antenna (or where it is in cars other than Avant) is not in the best place for great reception. I doubt Brodit will admit to knowing about this to an end user. DAB still has a fairly small adoption in the UK car market so I would guess Brodit know about this but will keep it dark until existing stock of current models have sold out of the warehouses or DAB users increase and it becomes a significant enough problem for them to address properly. Other makers will be doing the same. All of their products will have been tested for EMI radiation and RF interference that can be injurious to health and equipment like pacemakers and the like but not for soaking up low power DAB signals.

    That's my slant on it as someone who works for a large corporate professional digital media company.
    Admit nothing. If you can't fix it, feature it. If you can't feature it, kill it. If you can't kill it, best admit nothing.

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    Thanks for the detailed answer. I guess that all makes sense. Its weird that it does not affect the signal if you use a USB cable but then I suppose the current would be lower - maybe?
    Current: 2013 S4 Avant, Ice Silver, SS heated seats, tech pack, AMI, B&O.
    Previous: 2011 Mercedes C350 CDI Saloon

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    Quote Originally Posted by gr4z View Post
    Thanks for the detailed answer. I guess that all makes sense. Its weird that it does not affect the signal if you use a USB cable but then I suppose the current would be lower - maybe?
    Sorry, i go overboard sometimes. This sort of problem is difficult to chase down. Anything is possible really. The phone will usually pull as much current as it needs. What usually happens with car chargers is they have an overcharge sense wire or that measures the volts at the device end of the cable that feeds back to a regulator that regulates the output. If if it doesn't do that the charger could be generating full tilt. What could have an influence is the length of the charger cable if it's acting as an antenna. A longer or shorter lead may be different. Or maybe the USB lead is designed to carry data and is shielded but the charger lead isn't and becomes a loop when connected to the phone.

    Did you ever notice a difference depending on where you put the phone or how stretched out the lead was? You could try a lot of different tests like coiling the lead around the phone to make it less antenna like. Another test would be to plug in the charger and phone but pull the 12v accessory fuse to see if it still has an effect if not powered. But maybe easier to go back to a USB charger ;-)

 

 

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