We've just fitted a new aftermarket head unit to my 2003 B6 S4...
In the car are two aerials: one ISO and one Fakra - and the old unit was a Symphony II and had the same connections.
The new aftermarket unit just has one ISO and comes with a booster which has two FAKRA in to one ISO out plus a blue wire for a 12V feed.
So, we got a ISO to Fakra adapter to convert the ISO in the car to FAKRA to be able to plug in to the booster. So the booster now has both original aerials coming into it, and then out to a single ISO in to the new had unit.
We're getting a very crackly and poor radio reception. So, tried a second type of booster, which is just ISO to ISO with 12V (FAKRA not used) and had similar results.
Now, we know that these have diversity aerials fitted into the rear screens. We've had a look and there appears to be one on BOTH of the rear side screens (it's an Avant!) and not the rear screen as expected. Have we located the correct ones? We checked the power and they are both powering ok.
Now, does anyone know if the diversity aerial (i.e. the FAKRA) is needed for radio reception? We assume it must be as reception is poor without it!!??!
Is there a diversity control box or anything like that? i.e. the signal from the rear screens - where do those signals go? Direct to the rear of the head unit, or is there a control box in there somewhere???
We're really stuck and would appreciate any help!!!
We noted that the car had been retro-fitted with a phone aerial which is stuck to the inside of the windscreen. We're wondering if that install changed any of the wiring for the rear diveristy aerials to allow reception for the phone?
But, if this is the case why did the original head unit have perfect radio and this new one terrible reception?