View Full Version : I think I found the central locking unit Antenna for extending the remote range

02-11-2015, 11:07 AM
I've been trying to find the central locking unit( remote locking receiver) antenna recently.
As u know the range of fob is ridiculously close, I was actually surprised when the first time I got hands on my 97 2.8QM, it was only 8 meters away.
Recently, I read online that if u remove the rear seat cushion and there will be a black box with an antenna that only have one end attached back to the box.
After extending this antenna the range should get improved.

I didn't find this thing on my car, someone said this only applies to 96 model,and my car is early 97.
On 2000 a4, it's located next to the passenger side rear bumper, this does not apply to mine too.

I found this post,http://www.audizine.com/forum/showthread.php/334974-Keyless-Remote-not-working-Found-out-why ,
this technical bulletin for 98 a4 https://web.archive.org/web/20030323123857/http://mach.mach-nine.com/gti/vwtechcontent/audipdf/57-98-02.pdf,
eBay picture of the 8L0862257B central locking unit, along with the pic of replacement antenna from audi http://s67.photobucket.com/user/brbazemore/media/Clients/Town_Audi/CIMG0798.jpg

After cross referencing, I removed the cover of my passenger side light, and the mat.
I found the central locking unit, 3 connectors on it, I removed the L shaped connector ( it does have a curvy end I don't how to call it) which has 12pins 6+6.
After dissembling the connector, I found the two gold colored pin is connecting to a black shielded wire(like TV cable but way thinner),
the inner one has transparent rubber protectionand I guess that is the one should be extended.

I did not actually do it, since it's minus 15 today in Edmonton, and I pulled the battery for I'm not driving it recently.
I am planning to peel the antenna and solder a broken earphone as antenna, when it's warmer outside. Once I found if this works I will update is thread.

Almost every reference is archived into way-back machine.

I just find a pdf in german which explain how to mod the Antenna.

02-11-2015, 11:25 AM
My stock '01 works from quite a far distance. It isn't quite solid enough to roll the windows down unless I'm pretty close though.

Would like to see somebody run theirs to a "through the glass" cell phone antenna in the back window. Then obligatory Youtube video of hitting panic mode for a car so far away you can just barely hear the alarm.

Mad Cow
02-11-2015, 12:53 PM
I've been looking into something like that, my range is just abysmal, I can be touching the car with one hand and it still won't get a solid enough signal to open/close the windows. Problem is I know absolutely nothing about RF or antenna design. I've tried extending the wire and running it across the bumper like I read somewhere but that only raised the range to a few metres, which is still weaksauce. From the reading I've done it uses a pretty common frequency so there might be a premade solution out there somewhere that would just require a bit of soldering and creativity.

Any electrical engineers here that could help?

02-11-2015, 01:01 PM
MetalMan might know something. He's an electrical engineer, afterall.

02-11-2015, 01:04 PM
MetalMan might know something. He's an electrical engineer, afterall.

Well, mechanical actually. Don't think I could help much other than to suggest changing the antenna's length so that its new length is divisible by its old length. That way you can attempt to keep it optimal for receiving the proper wavelength(s). For example, if the original antenna's old length is 1 foot, make the new length 2 feet.

02-11-2015, 01:12 PM
Oh, haha. I thought you were electrical. Awkward...

02-11-2015, 02:40 PM
780 [up]

I have a 97 as-well and have been wanting to extend the range. Could we get some pictures?

Mad Cow
02-12-2015, 10:15 AM
So I looked it up again, my specific fob operates at 315-316 mhz but apparently the centre of the frequency range is 315 mhz. Maybe the 315-316 is a typo or some weird formality, I don't know. There's lots of useful info since it's a really common frequency, this (https://www.enocean.com/fileadmin/redaktion/pdf/app_notes/AN105_315MHz_ANTENNA_DESIGN_22Dec11.pdf) would probably be a good start.

02-12-2015, 10:56 AM
My '98 is somewhat decent, I can lock/roll up windows from about 20-25ft. Simply attaching a wire to a pre-existing antenna will not grant you much more distance (if any), my best guess is you would have to remove the pre-existing antenna and replace it with a newer one. Those who have extremely small distances likely either need a new remote battery, or I guess it's possible the antenna has corroded over time and lost distance that way.

Mad Cow
02-12-2015, 11:14 AM
I still got crap range with new batteries, my antenna is pretty corroded so maybe it's that. After doing some more reading I found that an inverted-v dipole antenna would probably be the best bet. All you need is some coax cable and 2 21cm lengths of wire in a v-shape with a 45 degree angle. Should be able to fit it in behind the rear bumper no problem.

02-12-2015, 05:34 PM
Double your range by touching the fob to your chin...

02-12-2015, 06:57 PM
I know nothing about antenna. But soldering a wire to it, is worth to try. The wavelength of 315mhz is 95cm, the original antenna should be around 24cm. Cellphone us earphone as antenna for FM radio and it's about the length.

02-12-2015, 07:29 PM
Wouldn't you want a solid wire vs the stranded ones on the earphones? BUT I used some 22 or 24 gauge solid. Extended range by 5feet lol.

02-12-2015, 07:44 PM
Double your range by touching the fob to your chin...

This actually works quite well, I use to do it when I drove my passat because it had terrible range. But I just feel like an idiot when I do it in public...

Mad Cow
02-12-2015, 08:04 PM
The type of wire doesn't matter much, solid is better only because it keeps its shape. I just finished soldering 2 pins to a new coax wire, tomorrow I'll run it to the bumper and make an antenna. From the reading I've done it seems that the stock antenna is a terrible design so basically anything should be better.

I miss the Compustar system in my old car, even from a block away without a clear line of sight it worked 100% of the time, and that was with the antenna inside the dash and not at the top of the windshield like recommended. If I can get even half that range I'll be more than happy.

02-16-2015, 06:40 PM
So today I finally figured this out, just like the plan I soldered a earbud cable to the old antenna. It really improved the range, from 3-5 meter to around 15-20 meter. At least the panic works really well (It's really hard to find my car in mall parking lot)

New range, Idk how far it actually is.

u can see the cable that hanging there .

Closer look for what I've done. Later I found a drain hole with rubber plug and made the cable went through it. It settled in the plastic rear bumper cover. I also kept the old antenna.