E92 key remote range: one solution

superwofy

Corporal
Jan 18, 2021
103
134
0
Hi all,

Wanted to share a small fix I developed yesterday for the E92. It's not a DIY per se, but should be easy enough to follow.

I've been having key range issues since around 2018 when the rear window was tinted. Can't really determine if the antenna was slightly cut or perhaps the tint is metallic. The Diversity amplifier is functional and the FBD wiring to the CAS is not damaged.

In any case, I wanted to fix it without changing the rear window or removing the tint. To that end, I saw two choices:
  • Fit an E93 mirror which has the FBD receiver inside and wire to the CAS. Not too difficult, 30G from FZD must be wired to 30 (BAT+). May not work great with tints and climate windscreen.
  • Design a new antenna and bypass the rear window aerial.

Initially I chose to create a new antenna. Simple enough, 868 MHz 1/4 wavelength antenna length should be 173mm. All I would have needed is a coaxial cable and a place to put it.
I then realized that there's an unused GSM antenna in the shark-fin. That GSM broadband antenna is tuned for 850/1900 Mhz - close enough. It's also vertically mounted, has a ground plane and is outside of the car's Faraday cage-like environment.

All I needed was a 90deg fakra G connector on a short (~10cm) RG174 coaxial cable. I had an old pigtail that matched this description. So I stripped a short piece of the coax cable, shielded it and soldered to a capacitor I moved on the Diversity board and to GND. The cable is then routed through a opening I made in the Diversity's upper casing near the TV connectors.

New key range is at least 30 m.



If I had to do it again, I might use a thinner cable such that I can fit it under the Diversity board. The cable is heavily shielded but still quite close to the pins of some amplifier chips.
I don't know how well this would work for 315 or 434 MHz remotes.
 

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superwofy

Corporal
Jan 18, 2021
103
134
0
I "measured" the range to be about 60-70 m from the fin with an unobstructed view, a new fully charged starting battery and a standard CA remote with a CR2050 battery that's a few months old. YMMV.

Definitely recommend that Visual, Acoustic acknowledge (CIC) are coded and enabled and that auto re-lock (CAS, VER_AUT_X_MIN_OHNE_NR) is too with this range.
 
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