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Rear Window Radio Amplifier/Booster - HELP NEEDED!!!

Lion Heart Aug 3, 2011

  1. Lion Heart

    Lion Heart Member

    Hi guys

    Quick question for my B6 S4 Avant...

    I've replaced the stereo with an aftermarket version, but am getting a VERY poor radio reception.

    Now, there are two aerial leads behind the stereo, one ISO and one FAKRA. The main one being the ISO (like a normal aerial plug).

    The new head unit (all singing and dancing with Sat Nav, DVD, touch screen, bluetooth etc) only has one aerial input (ISO).

    There was a 'booster' supplied with the aftermarket unit which basically has two Fakra inputs on one end and it goes out to one ISO on the other end (which plugs in to the new head unit), and also has a lead for a 12V feed.

    So, I had to buy an adapter to change the ISO to FAKRA so I have two Fakra's essentially coming from the car end now...

    I gave it the 12V live feed, but sounds aweful...

    I've tried swapping the two (now FAKRA) connectors around but it only works one way around. Also noted that if I unplug the secondary aerial from the booster it makes NO difference. So the secondary aerial (the original FAKRA one, not the ISO one) may as well not be attached to the booster at all!!!

    Now, correct me if I'm wrong guys, but the secondary aerial is linked to an 'amplifier' or booster which is built into the car as standard and sits at the top of the rear screen?

    And it's this secondary aerial that ensures a good quality signal.

    Now, my set up is basically aerial 1 connected, and secondary aerial not connected.

    It made sense that the booster (aftermarket) needs a 12v feed as I assumed it would send 12V to the amplifier above the rear screen???

    What the hell is going on, and any ideas why my set up is not working, and what I can try to fix it????

    Does the original Audi head unit do anything with the signal received from the secondary aerial cable (and booster near the rear screen)???

    Help please guys!!!

    Many thanks!

    Lion Heart :)
  2. BahnStormer77

    BahnStormer77 BahnStormer

    the booster near the rear screen is a well known failure point.... if your aftermarket kit has a booster, then try to bypass the Audi one entirely... just an idea, but it may work...
  3. AndyMac

    AndyMac Moderator Staff Member Moderator

    No just ignore the fakra aerial, it does very little. You need the ISO lead connected to an Audi antenna amp adapter fed with 12v from the HU power antenna feed. The adapter takes the 12v feed from the HU and feeds that down the coax going to the antenna amp in the boot.
    ISO Active Aerial adaptor - Fitting Adaptor
  4. Lion Heart

    Lion Heart Member

    Hi Guys!

    Hey - AndyMac, thanks for that - VERY useful info!!!

    Ok, so to confirm, the FAKRA plug can be ignored completely? What was it originally designed for - I assume it must have some function? I think it's also called a 'diversity' aerial?? Any ideas very welcome!!!

    So, back to the ISO. The rear aerial is powered from the ISO and not the Fakra? That's very good to know as I assumed it was powered via the FAKRA. So thanks for that also!

    To confirm: the ISO feeds the rear window antenna amp down the centre of the coax - the same one from which it receives the signal? Does it do this direct, or does it go via the main rear amp located in the right hand side compartment inside the boot (mine's an Avant)???

    I ask this because when I first set it up the rear main amp was not getting power and so the rear speakers did not work. So I had to take a live feed to power the main rear amp. So my thought is the issue may be there if this sits between the HU and the Aerial Amp?

    But if it's via coax you would think it connects directly from the HU to the Aerial Amp?

    I'm going to buy one of those adapters right now. It's different to the one I have, but I suspect the principal is the same. I'm getting this one:

    CT27AA05 Aerial/Antenna VAG Active ISO Adaptor - Instal | eBay

    Many thanks!!!

    Lion Heart
  5. BahnStormer77

    BahnStormer77 BahnStormer

    Has anybody tried sourcing the original Audi aerial booster from SEAT?

    I was quoted £140+VAT from Audi...

    But then found it on the Russian version of VAGcat that allows you to see much more recent models, incl the Seat Exeo: Каталог автозапчастей VAG

    So I'm guessing that we can use those same parts, but does anybody know which revision I would need?
    8E5035225P @ 9771.06 руб. (£200)

    8E5035225AF @ 5109.68 руб. (£105)

    Take those prices with a pinch of salt - I jsut want to knwo which part number to go for and then I'll ask Seat what they're charging - have YET to find a matched part from Seat that cost as much as Audi charge.

    I've been reading up on it a bit and it would seem mine falls into a grey area of being an early B6, but with a 2007 RNS-E (8E0 035 192 K)... any ideas?

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