Antenna Design - Fenix 5/5S vs. 5X vs. Chronos vs. Fenix 3

Former Member over 8 years ago

There's been a number of reported GPS/Bluetooth/ANT+ complaints and issues with the Fenix 5 and 5S so I took a look at some FCC docs to try and glean some information. Before we get started, please note that everything listed here is from generally crappy FCC pics and basic deductive reasoning, so please take with a grain of salt. Some background:

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 (inductively?) 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 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.

0 Former Member over 8 years ago

Looking at the main boards of the F3, Chronos and the F5 family, a few thoughts jump out:

The F5 is more similar to the F3 than the Chronos. The F5 board looks like the F3 board if you took the Bluetooth/ANT+ and Wifi ICs and moved them into the shielded area
The F3, Chronos and F5X all share the same PCB antenna design for the non-GPS antenna. The F5 and F5S have a different (but still PCB antenna) design
The F5 and F5S boards look pretty much identical except for some minor changes here and there. The 5X board and ICs look substantively different despite being part of the same family. I wouldn't be surprised if the processor, RAM, storage and other subsystems are different than the 5 and 5S
While Garmin claims its Exo antenna is omnidirectional it seems odd that they've placed it at the 12 position. Given that most folks are right handed and will wear the watch on the left wrist, it seems placing the antenna at the 6 position would make more sense as that is what is facing up when people are running

Anyways, more questions than answers, but thought I'd share this info with the board to see what other people think or what information others have. A few more questions for this forum:

Given the new design of the non-GPS antenna on the 5 and 5S, that would be one potential explanation for the reported Bluetooth/ANT+ issues/dropouts that people are seeing. The 5X appears to retain the non-GPS antenna design of the F3 and Chronos. Are 5X owners seeing similar Bluetooth/ANT+ signal strength drop out issues?
There's not much activity in the Chronos forum. Are Chronos users happy with its GPS performance compared to the F3? If so, that would give some credence to Appelmoessite's article about the Chronos' GPS improvements

Appendix:
Fenix 3 FCC Internal Photos
Chronos FCC Internal Photos
Fenix 5S FCC Internal Photos
Fenix 5 FCC Internal Photos
Fenix 5X FCC Internal Photos

0 webvan over 8 years ago

Thanks for sharing the detective work. A quick thought on the comment about the "smile" antenna being placed a 12 and therefore not ideally for a left-handed person, does it really matter since the bezel is apparently supposed to act as an "EXO Antenna" by being inductively connected to that "smile" antenna ?

0 chimpware over 8 years ago

Are you sure the antenna design is the same in the 5 and the 5s? Give the bezel on the 5s I was thinking the design of the 935 and 5s might be more similar. I have not seen a lot of data posted by 5s users to determine if there is a difference in GPS performance between the 5 and 5s.

0 marcusjahn over 8 years ago

GPS Performance 5S

Are you sure the antenna design is the same in the 5 and the 5s? Give the bezel on the 5s I was thinking the design of the 935 and 5s might be more similar. I have not seen a lot of data posted by 5s users to determine if there is a difference in GPS performance between the 5 and 5s.

Here you have a track from the 5s, i´ll return it tomorrow :mad:

https://connect.garmin.com/modern/activity/1682042088

0 chimpware over 8 years ago

That track does not look bad to me at all. There are spots where it is off it seems, were you run / walking or is the pace chart that bad?

0 Tommylee84 over 8 years ago

That track does not look bad to me at all. There are spots where it is off it seems, were you run / walking or is the pace chart that bad?

I'm with you on that, I would look at that and go yea that where I ran. Yes there are some spot that it drifted but you are wearing something the size of an oreo that communicating with a satellite mile (kilos) away asking for it to be perfect.

0 Former Member over 8 years ago

Are you sure the antenna design is the same in the 5 and the 5s? Give the bezel on the 5s I was thinking the design of the 935 and 5s might be more similar. I have not seen a lot of data posted by 5s users to determine if there is a difference in GPS performance between the 5 and 5s.

The 935 FCC docs aren't available yet so nobody knows unless someone offers to crack open their Forerunner. The antenna design between the 5 and 5S should be similar except for Appelmoessite's claim #1 that the bezel doesn't have any screws on the Chronos which is the case in the 5S as well. My guess is it's the same EXO antenna inductively connected to antenna 2 which is connected to the mainboard via 3 spring clips.

The 935 doesn't need a 'first' external antenna given that it's made completely of plastic. My guess is that it has a much more traditional and simple loop, patch or trace PCB antenna inside the watch case.

0 Former Member over 8 years ago

Thanks for sharing the detective work. A quick thought on the comment about the "smile" antenna being placed a 12 and therefore not ideally for a left-handed person, does it really matter since the bezel is apparently supposed to act as an "EXO Antenna" by being inductively connected to that "smile" antenna ?

Someone with a better understanding of physics needs to chime in here. My speculation is that while the two antenna parts form a single overall antenna structure, each part of the antenna is capable and optimized for receiving GPS/GLONASS wavelength RF. So if the second 'smile' antenna was placed at the 6 position, it could still receive GPS RF given it's sitting behind the plastic watch body.

0 marcusjahn over 8 years ago

That track does not look bad to me at all. There are spots where it is off it seems, were you run / walking or is the pace chart that bad?

It was an easy run with constant speed, the track is ok for me but the pace cart is a joke

0 mcbadger over 8 years ago

Thanks for sharing the detective work. A quick thought on the comment about the "smile" antenna being placed a 12 and therefore not ideally for a left-handed person, does it really matter since the bezel is apparently supposed to act as an "EXO Antenna" by being inductively connected to that "smile" antenna ?

The internal antenna will be pointing towards the ground whether you're left-handed or right; left-handed folk don't wear their watches with the face upside down. :) As for the rest...

Someone with a better understanding of physics needs to chime in here. My speculation is that while the two antenna parts form a single overall antenna structure, each part of the antenna is capable and optimized for receiving GPS/GLONASS wavelength RF. So if the second 'smile' antenna was placed at the 6 position, it could still receive GPS RF given it's sitting behind the plastic watch body.

... my experience with interacting RF antennae is at lower frequencies (about 60-400MHz), but I would expect antennae interacting like that to cause frequency shifts, and it's possible that the spacing between internal and external is carefully set to leave the combined structure spanning GPS and Glonass frequencies. That said, nobody's broken down a bezel as far as I know but they don't appear to be anything but a metal ring, with nothing obvious to tune them other than the length of the loop, which isn't even the same across the three F5 models. I posted recently some links to patch antenna design, but it's not clear to me what's going on. Thank you for posting those patents - that's the most informative thing I've seen about the design.

ETA: I didn't read far enough into the patent; it says that the length of the loop is indeed intended to tune it to the wavelength (19cm for GPS and Glonass, near enough, which makes me think the bezel is a little bit small for that to work optimally).