Hissing / poor signal (intermittent) FM Radio

lsuhe

Registered User
I've had my 8v sportback for just under a year. It was an ex loan car, and specced up including tech pack with connect. It was built Feb 2013 so does not have DAB. :( The FM radio on it has been great in terms of signal quality and ability to pick up many different stations. Then a few weeks ago just one day the radio started to have poor signal on all stations, not just local ones like Radio Nottingham and Capital FM, but national Radio 1, 4 and anything I listened to. The area I drive has not changed and in all the cars I have been in around the Nottingham area had no issues in picking up local FM and national FM stations.

I took it into the dealership and tried to demo it, and of course being intermittent fault it barely managed to display itself. They performed an update on the MMI software, but I didn't think this would fix it. I got in the car after getting it back and within less than a mile the problem had come back. I then recorded about 12 minutes of audio to play back to the dealership so I can demo what the problem sounds like. Even stopped at a junction the signal can drop out and come back even though nothings really moving around me. Its as if there is a poor connection somewhere from the aerial to the MMI/head unit.
Has anyone else had similar? The only way I see they could fix this is to replace the cable that goes from the FM aerial (is that in the read windscreen?) to the head unit and take apart quite a few side panels of whatever route the cable takes... Does anyone know?

Many thanks in advance.
Chris
 

veeeight

I am a very pretty girl
VCDS Map User
^ I like where you're going with this !
 
Let's just say I've been caught out like that myself in the past. I had to rip the guts out of a power adaptor for a GPS speed camera device and replace it with something less high-tech but considerably quieter... ;)

Adapter.JPG
 

veeeight

I am a very pretty girl
VCDS Map User
The other "test" I would ask the OP to do, is to find an area of good reception, then switch on the heated rear window. Does the reception then go hissy?
 

m0sbf

Registered User
Let's just say I've been caught out like that myself in the past. I had to rip the guts out of a power adaptor for a GPS speed camera device and replace it with something less high-tech but considerably quieter... ;)

View attachment 36540

Lovely, a 7805 what a blast from my electronics past!
 

rich dj

2015 A4 Avant 2.0TDI SE Quattro 190 Technik
I have noticed poor FM when I plug in a USB adapter one 3 different brands so looks like the 7805 might be the way to go too.
 

m0sbf

Registered User
Like the fact he added decoupling capacitors to his 7805 circuit board. Obviously knows what he is doing :)
I have some 7805's in my junk box, so might get my soldering iron out and try this out...
 

veeeight

I am a very pretty girl
VCDS Map User
You just need to be a little careful with heat dissipation, much as I hate SMPS, they are more efficient (and cooler) than linear regulators. But so many cheap SMPS adaptors have useless RFI rejection circuits, that's why they are noisy.

:(
 

dentsy

Loving my new to me allroad
The other "test" I would ask the OP to do, is to find an area of good reception, then switch on the heated rear window. Does the reception then go hissy?
I get this on my B7 avant rear heated window on radio reception gone 😞

what could it be ?
 

veeeight

I am a very pretty girl
VCDS Map User
^ one of the elements of the heated rear window / antenna has gone open circuit.
If you look closely, there might be physical damage evident.
 
If you're after a dual USB adaptor that I have tested under full load on the bench with 'scopes on it to ensure that it doesn't generate any nasty RF interference, I can personally recommend this one:

PowerJolt Dual Universal Micro - for USB-charging devices | Griffin Technology

DO NOT buy it from anywhere but the link above - not even from Amazon. I haven't been able to convince myself that any of the ones not actually sold by Griffin are legitimate. If it's less than fifteen quid and not in a box, it's almost certainly a fake. I bought a real one and a fake one to compare and they were frighteningly similar physically.
Griffinx2.jpg
Can you spot the real one?

Here's the real one under full load (scale is actually 0.1V/div):
Griffin_Real.jpg

And the fake...
Grifffin_Fake.jpg
See all those spikes? They're what generates wideband RF noise that splats your radio signals.
 
Like the fact he added decoupling capacitors to his 7805 circuit board. Obviously knows what he is doing :)
BBC engineer for 27 years. ;)

I have some 7805's in my junk box, so might get my soldering iron out and try this out...
Worth reminding people that, as others have mentioned, the 7805 is a linear regulator so will run hot. I wouldn't use one in a phone charging circuit unless you can mount it on a heatsink. It's only good for about an amp too. My application was powering a GPS receiver, so only a few milliamps to worry about.
 

lsuhe

Registered User
If you're after a dual USB adaptor that I have tested under full load on the bench with 'scopes on it to ensure that it doesn't generate any nasty RF interference, I can personally recommend this one:

PowerJolt Dual Universal Micro - for USB-charging devices | Griffin Technology

DO NOT buy it from anywhere but the link above - not even from Amazon. I haven't been able to convince myself that any of the ones not actually sold by Griffin are legitimate. If it's less than fifteen quid and not in a box, it's almost certainly a fake. I bought a real one and a fake one to compare and they were frighteningly similar physically.
View attachment 36655
Can you spot the real one?

Here's the real one under full load (scale is actually 0.1V/div):
View attachment 36656

And the fake...
View attachment 36657
See all those spikes? They're what generates wideband RF noise that splats your radio signals.
I have the same problem it seems. After some testig I have a "Belkin" adapter I bought off amazon, which works fine, but unfortunatley does cause this white noice interference to the FM radio. I did some testing plugging in and out whilst charging my phone and can confirm i have an adapter which appears to be a non genuine one or at least i believe it is causing the intereference with the FM radio. I have changed back to my maplin 1amp adapter and no longer have the FM radio interference issues. So gutted as bought 3, a spare and one for my wife as recommended my my brother.. who barely uses his FM radio in his yarris. Still not the end of the world and I am glad that the radio is not faulty but just working as expected.

Many thanks for everyones helpful and kind replies. Thanks to all
Chris
 

veeeight

I am a very pretty girl
VCDS Map User
Glad you're sorted. Cheap cigarette lighter power adapters really are the pits.

Those and the numerous fake SD / memory cards available on popular online auction sites. :(
 

jasonc

Registered User
I had radio interference problems in my last car with various cheap and then fake adapters. For a well made interference free adapter I can recommend the Scosche adapters:

http://goo.gl/MplgXZ
 

N17ELE

Registered User
Did you have any kind of phone charger or similar plugged into the lighter or power socket?
What a star you are. Reception on my C6 went terrible, i changed the amplifier and no change. Then read your post and remembered that I have fitted a double usb onto the cigarette charger. I pulled it out and all perfect the usb is labeled as a Griffin, but since off eBay could be anything. Thanks for the tip.
 
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