Electro experts: how to improve reciever sensitivity?

[sipman]

So after my service tech told me to bring both key fobs in to try and identify why the remote key fob reception is so horrible, I discovered the TSB on the mirror problem in my coupe.
For those that don't know, apparently, the solution is to install a interior rear view mirror from a roadster into the coupes, and the distance/sensitivity of the remote entry system is greatly increased.

Well, it turns out it's too late for me and the service manager says he won't replace the mirror under warranty. It's either live with it, or shell out $600 for a roadster mirror/install.

I was thinking that maybe adding antenna length to the receiver inside the mirror would improve the reception. I've seen videos online that show people adding a length of wire to the transmitter in the fob to improve distance. I'm guessing that's not the solution we need as the TSB says a different receiver is needed.

The big question is has anyone done this? Does it work? Is it as simple as soldering a length of wire onto the receiver body, or should a new receiver be installed?

I'm guessing if something like this works for the coupe mirrors, it might also work for the roadsters...

[gas-can]

Not sure about this particular car, but the idea that a roadster receiver is better than a coupe's is interesting. You would think that the coupe transceiver would be designed to be stronger b/c of the metal shell vs fabric roof on the roadster.... Maybe they are somehow using the roof to augment the antenna...?

One small note if you do decide to increase the transmitter's antenna length. These are usually precisely calculated traces on a pcb. (The tuning circuit usually uses the impedance of the antenna along with a small tuning capacitor to set a transmit frequency [gross oversimplification but basic idea]). If you were to just splice a random piece of wire, you may actually decrease your range b/c you may increase the amount energy reflected back...

If I recall correctly, the proper way would be to figure out the exact length of the transmitter and add a length of wire that is a multiple of that (eg: if antenna is 2m now, add another 2 to make the total length 4m). Or if you know what the frequency of interest is, adjust the tuning capacitance to compensate for the change in impedance.

I recommend that you try playing with the receiver in the car instead...may be simpler!

If you want more info, try googling antenna length tuning and SWR (Standing wave ratio).

gas-can