Chris
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The GTX345R location in the DA40 is almost diabolically designed to prevent Bluetooth reception. The transmitter is under the GARMIN label on the GTX345R, as shown by the black oval added with a Sharpie:
The entire rear shell, flange and deck cover of the extended baggage compartment rests directly on top of the GTX345R. And is carbon fiber. Which is fantastic for weight, but blocks RF, leaving only small "transparent" gaps around the perimeter of the shell. It is remarkable that any Bluetooth signal reaches the front seats.
This solution re-broadcasts the GTX345R output beyond the carbon fiber cocoon. Bluetooth uses the same frequencies as low-band Wi-Fi (2.4 GHz), which simplifies finding parts.
The only required tools are a #2 Phillips screwdriver to remove the baggage deck cover, and a 3mm hex driver to remove one shelf support screw. The latter is necessary to route an RF cable behind the shelf support.
The following parts list is a good starting point, but alternatives should also work fine. Just ensure that the connectors mate correctly. It is easy to confuse RP-SMA with SMA.
- Microstrip antenna
Digi-Key PN 994-1169-ND
Mfg PN MAF95310
$2 each
https://www.digikey.com/product-detail/ ... ND/5876486
- U.FL <-> RP-SMA adapter
Digi-Key PN ARF1585-ND
Mfg PN 901-10097
$11 each
https://www.digikey.com/product-detail/ ... ND/1012546
- 50cm RP-SMA extension cable
ASIN B00B91CRRI
$5 each
https://www.amazon.com/Kenable-Antenna- ... B00B91CRRI
- White Wi-Fi antenna (probably blends best with interior)
5 dBi
ASIN B01N3RVQRF
$8 each
https://www.amazon.com/Dericam-Universa ... B01N3RVQRF
- Black Wi-Fi antenna
9 dBi (slightly higher gain, but probably not material)
ASIN B00NVG5YZG
$8 each
https://www.amazon.com/TECHTOO-Antenna- ... B00NVG5YZG
Microstrip antenna positioned on the GTX345R. Perpendicular to the oval slot provided the strongest signal.
Installation with the rear baggage deck cover removed. This is the only access required. Plan to chat with my IA about drilling a small hole in the rear bulkhead ("minor mod") near the top of this photo (under the shelf support) to simplify routing.
Completed installation, but will replace the tape with a plastic clamp using the left trim screw: