Twin fakra aerial adapter -worth using?

[tadziak]

Hello,
I have a VW GOLF V from 2008, with an Alpine IVA-202r installed. My original antenna installation uses two atennas - one on the roof and one at the rear
shield (diversity). My question to you is if it is better to use the twin fakra aerial adapter and connect both antenas into the Alpine unit,
or its better just two plug one of the antenas, using standard single adapter (for 1 antena)?

Do those two antenas' signals sum up when using twin fakra aerial adapter or this adapter chooses which one is stronger and sends it to the radio? Does it really work or it might cause some additional interferences?

I would be very grateful if you could clarifiy that to me...

[richard@thebrae]

The diversity Antenna works like this :- The VW HU has a control circuit which senses which antenna has the best feed relative to the cars position and direction to the transmitter, it uses the line with the beige/brown connector to switch the antenna selection in a box of tricks in the rear of the car and send the appropriate signal up the wire with the white connector. See this :-
http://www.my-gti.com/1389

In my experiance the diversity adapter does boost the signal strength a bit, AM frequencys disappear, and I would say it is a necessity but a compromise on the origional oem reception which was excellent (rcd 300 unit) currently usind a chineses rns 510 clone.

[tadziak]

First of all, thank you for your complex answer. I have been looking all over the forums for anything specific about this matter and found nothing. Most people just connect one of the antennas to the aftermarket units and thats all.

I understand well what the original HU did, but I'm still not sure what does this adapter do exactly, how does it handle signals from two separate antennas. In this case there is no special circuit in the HU to make 'all the magic', so does it just sum up the two signals or chooses the better one and let it through to the radio antenna input?

Thanks a lot for claryfying.

[richard@thebrae]

The adapter is supposed to replace and emulate the control circuit that is in the oem HU, and there is various quality versions of this adapter varying in price from around £8 up to £25/30 pounds. I paid £22 for one from celsus via autosound and I would give it 8 out of 10 versus the origional oem setup.
I have tried many times to improve my radio reception as my local terrain is difficult for FM reception.
Although I have not tried this on my Golf my personal recomendation would be replace the passive rooftop bee sting antenna with a passat b5 or mk4 golf amplified bee sting rooftop antenna and if your alpine unit does not output the 12v line feed up the centre of the arial cable then fit an inline feed for around £10.
My passat b5 had this and it worked very well in the exact same local. It failed once due to water ingress and the performance dropped right off, and returned as soon as i replaced it.
photo of the water damaged ampified base attached. Hirschmann make an excellent equivelent amplified bee sting which is a little less exspensive than VW's they are No 1 for antennas in UE.

[tadziak]

Thanks a lot again for your percise answer. So there is some difference between those adapters in terms of quality? I have tested mine (the one on the picture) and it did not work too well, so I wonder if I should search for a more expensive one from one of the known brands... Maybe that would do the trick.

My rooftop bee sting is amplified and I believe those adapters already have the power suply of 12V to feed the antenna amplifier.

One more question - is there any simple way of making sure that my amplifier (in the antenna base on the roof) is fine and not damaged by water or something? I dont want to demount all the rooftop, because the car is quite new (2008)...

Would you stay with original VW antenna or rather replace it with some other manufacturer?

[richard@thebrae]

Hi, I am surprised that your MkV has an amplified rooftop antenna,as all of the info I have seen on MkV's display a passive one, that is not to say you are wrong, but I would check.
If you had your OEM HU and a VagCom Lead this would tell you for sure as it interrogates the antenna amp via the radio.
I am sorry to say that the adapter in the pic looks like a poor quality version and is probably not a diversity function unit and nothing more than some sort of fiter/resistor combiner.
I know a guy who is an electronic specialist who opened up a chinese made one like you have, and that is what he found and it was a rubblish circuit(there is one similar to it on the celsus site @ £15, but is propably better quality)
Have a look here for the celsus version with diversity function @£20 :-
http://www.celsusice.co.uk/products.php
My experiance with the VW amplified unit was good on my Passat and would be happy to use one again.
Hirschmann is also one of the oem suppliers to VW but when it comes to combo antenna's (gps/phone/radio/dab) they are the leaders. google them for info.
I have not fitted an amplified bee sting on my golf for the same reasons as you :-Getting at the antenna base and running a lead to the radio and poking about with the trim and headlining is probably a nightmare.

[tadziak]

Hi,
Thanks again. Actually maybe that is a big part of my problem that I'm supplying the 12V on the antenna which in fact has no amplifier and therefore doesn't need the power? Can supplying the "not-needed power' that cause problems with reception or do any harm?

But I guess that GOLF V has some amplifier somewhere? Is it in the rear shield?
I had the power supplied for the antenna because we found out at the begining that it helped with the AM reception...but now I'm not so sure anymore...So whats the best way to check it, just unplug the power and test on AM stations?

[richard@thebrae]

Hi,
Thanks again. Actually maybe that is a big part of my problem that I'm supplying the 12V on the antenna which in fact has no amplifier and therefore doesn't need the power? Can supplying the "not-needed power' that cause problems with reception or do any harm?

But I guess that GOLF V has some amplifier somewhere? Is it in the rear shield?
I had the power supplied for the antenna because we found out at the begining that it helped with the AM reception...but now I'm not so sure anymore...So whats the best way to check it, just unplug the power and test on AM stations?

12v up the line in a passive antenna would do no harm as long as that line was not bridged to earth.
It could help with the AM signal like other live signals in wires picking up RF but it would also be noisy unless filters were applied.
The golf has an amplifier on the rear screen antenna and its location is in the rear door as is the diversity switching box.
This amp also uses AM filters and no AM signal will pass from it.
I totally lost all AM signals with the diversity adapter, but as i never use it i dont care.
I stand by suggesting the use of a good amplified roof top, but agree the hassle of fitting it is a daunting prospect as both rear piller trims have to come off, the roof lining has to be dropped to get at the antenna base and a new signal cable will have to be routed via the roof lining to the fron A piller then to the radio.
Perhaps you can try a cheap windscreen mounted unit like this :- http://cgi.ebay.co.uk/ws/eBayISAPI.d...=STRK:MEWAX:IT

[tadziak]

Hi,
I called my VW dealer and he also confirms that there is no amplifier on the rooftop, so powering that antenna was not a good idea So powering 12V on a passive antenna could improve the AM reception, even though there was no amplifier to power? That's really interesting...

Just last question. So as I understand, 12V on the passive antenna may cause some additional noises? And if I use that diversity adapter, would it give 12V to both antennas? Wouldn't it cause also some problems with the reception/noises for that passive antenna?

[richard@thebrae]

Hi,
I called my VW dealer and he also confirms that there is no amplifier on the rooftop, so powering that antenna was not a good idea So powering 12V on a passive antenna could improve the AM reception, even though there was no amplifier to power? That's really interesting...

Just last question. So as I understand, 12V on the passive antenna may cause some additional noises? And if I use that diversity adapter, would it give 12V to both antennas? Wouldn't it cause also some problems with the reception/noises for that passive antenna?

Voltage on the line would cause some EMF which might pick up some AM frequencys better than having no Voltage on the line, but in no way is it an amplifier just a better recepter of RF..
Again the 12v on the line may pick up random and local frequency's such as fluorescent lights ect which will come through as background noise.
My experiance with diversity adapters is that it puts 12v on both lines
The extra noise on the AM input would not be a problem as the tuner filters would kill the the noise. especially when tuned in to a station.