- GPS, Bluetooth, ANT+, Wi-fi are all based on electromagnetic radiation; their wavelengths are just different
- When transmitting and receiving aforementioned electromagnetic radiation, or radio frequencies in this case, the more power and sensitivity the better, leading to a higher signal to noise ratio
- When it comes to industrial design, some materials are RF opaque and some are RF transparent. This is why your aluminum iPhone (RF opaque) includes those plastic antenna lines (RF transparent) to allow it to transmit and receive
- This obviously presents a challenge for watch makers like Garmin who want to use premium materials like metals in their design. Garmin's answer to this is their branded 'EXO' antenna which essentially embeds an external antenna into the metal watch bezel and then connects it to a second antenna inside the watch case. Garmin's patents in this space are a good background read on their design and approach. Patent one and two
With regards to GPS, Garmin has now used the EXO antenna in three different sets of hardware, the Fenix 3, Chronos, and now Fenix 5. The Fenix 3 developed a reputation for having poor GPS performance, and according to this article by Appelmoessite, Garmin addressed many of these issues in the Chronos. The claimed improvements:
- Redesigned EXO
stainless steel bezel, screws moved to the bottom leaving a nice round bezel on top.
- Redesigned EXO “spacer” / real antenna. Inside the Chronos is the antenna which has the shape of a smile which someone once called the “spacer”
- Antenna mounted on main PCB board. No big springs to make contact with the antenna, everything has made smaller which better controlled connections.
- Redesign of “1st stage” electronics to better match the antenna and receiver IC.
- Redesign of “2nd stage” electronics, receiver IC (MTK) with corresponding passives.
- Second shielded main room for all the other electronics.
- Redesigned ANT+ / Bluetooth antenna which is on the other far end of the PCB so the influence on the GPS is minimal.
In terms of the alleged Chronos improvements and whether or not they trickled down to the Fenix 5 line: based on the FCC internal photos, it seems that 3 and 7 are not included in the Fenix 5. In the F5 the second antenna is still connected to the board with springs and the GPS chip (Mediatek MT3333?) is still in the same EMI shielded compartment as all the other ICs, not spaced off into its on compartment on the Chronos. That being said, the 5X board appears to show a chip that may be in its own shielded compartment, but it's not possible to tell if it's the GPS chip or if it's fully shielded in its own compartment. It's impossible to verify 1, 2, 4, 5, 6, and 8 from the docs in FCC photos, but there's enough here that I tend to believe Appelmoessite's claims.