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935 sensor dropouts

I have experienced sensor dropouts with my Kickr power reading, cadence sensor, heart rate and speed. Below is a bit of summary where I am trying to figure out what may case the dropouts. I suspect that software (using 4.10) or hardware is causing the 935 to be more susceptible to ANT interference. To date, I am also unable to connect my 935 to my Kickr over Bluetooth despite following recommended suggestions.

Ok, I have done some more testing today to try and figure out what is going on with the 935 sensor drops. I tried to eliminate all factors that could impact the readings. So today is did 3 rides of 10 min each at a constant cadence (as far as possible).

My Setup
- 820 = mounted on my handle bar close to my stem.
- 935 = on my wrist, but I tried to keep my hands on the bars as close to my step as possible and did not move my hand while riding (just to keep some consistency).
- Rollers = Standard rollers with Garmin speed, cadence and heart rate.
- Kickr = Kickr transmitting power & speed, with Garmin cadence & heart rate.

Ride 1 - rollers -
First ride was on rollers on my porch by the pool. You can see that my 820 had 3 drops in speed and cadence. The drops did not happen at same time. Heart rate was solid with no drops. I guess it is because heart rate was close to device that any interference was ignored or signal remained strong enough. The 935 had a lot more drops at not predicable pattern.

Ride 2 - rollers - WiFi off -
Ok, so then I decided to turn all electronic equipment off that may cause ANT interference (like phones, WiFi, etc.). My closest WiFi was a Netgear NightHawk range extender at about 10 meters. Remember that it is located inside the house (TV room) and I am outside the house by the pool. The readings is perfect. Not a single drop from my Garmin sensors and my 820 & 935 is a match. This is pretty amazing and I was really surprised at the result. Maybe a range extender (2.4 & 5 GHz) is just too strong and cases issues.

Ride 3 - Kickr - WiFi off -
So now I remained in the exact same position, but introduced the Kickr. It was power by an extension cord while all other electronics remained off. The 820 had almost perfect readings with only 1 drop from power 30s into the ride. It also had some minor power reductions at 2:22, 5:50 and 9:07 into the ride. But this coincides in a slight drop in speed also (I think I may have slowed my cadence which was already slow-ish). Then if you look at the 935, dropouts in speed & power. Remember that both come from the Kickr. The cadence and heart rate was solid from Garmin. The speed drops seemed to happen every 210 seconds while the power was far more frequent at 90-95 seconds. There is a very real pattern here!

Conclusion
1. WiFi has a big influence on ANT devices, so try and stay away if you want good results. What was amazing was just the big impact as I thought I was ok being outside and relatively far from the device. Might be an option to reduce transmit power if you can deal with shorter range.
2. The 935 is more sensitive to interference or weak signals than the 820. Not sure if the 935 has the same hardware as the 820, but think not due to the form factor changes. Also not sure if additional hardware in 935 (like Bluetooth Smart sensor support, optical heart rate) cases a weaker ANT signal?
3. There is still something wrong in how the 935 deals with a weak signal coming from Kickr. Either the 820 has a better ANT receiver allowing it to ignore interference, or better software? What is clear, with the exact conditions, the 935 is more prone to drops.

I do not have an actual bike power meter, the Kickr is my only power source. So to really eliminate if this is a Kickr or Garmin issue, I will need to simulate this using a real power meter. I am a Zwatt backer and still waiting for my power meter, so will have to wait to test when I get it. Except if someone wants to send me a power meter to test. :D

The question remains, is the Kickr sending out weak ANT signals or causing interference that disrupts the 935? I am still unable to connect my 935 to the Kickr over Bluetooth (also another test to see quality of signal) as that will remove potential 2.4 GHz interference.

I am keen to hear what you think?

Cheers
Shane

0 CloggyAbroad over 7 years ago

ANT and WiFi work in the same frequency band (2.4 GHz). The frequency your bike sensors are on (ANT Channel 57, 2457 MHz) is the same as WiFi Channel 10 (on 802.11b), but any channel between 8 and 12 will have the ability to interfere with ANT signals. Could you try to set your range extender to a fixed channel outside channel 8 to 12 and see what happens then?

0 thigger over 7 years ago

Whilst you may have other issues, the power dropout every 90-100 seconds is a known issue with the Kickr and was introduced in a recent firmware update. You can downgrade to 1.3.32 ( I think that's the version!) but please email Wahoo and tell them you're experiencing this - they first acknowledged it to me months ago but keep saying they're working on a fix.

0 captainfranz over 7 years ago

I am experiencing tons of dropouts on my bike trainer with various PowerTap hub power meters. Readings from the Edge 500 sitting right next to the 935 are perfect, so this is obviously an issue with the 935. I am also experiencing the same dropouts outside, so that excludes wifi as well (and again, perfect readings from the Edge 500). So much so that I am even getting some occasional dropouts from the HRM-Tri. This is really disappointing. I understand this is a new device, but I don't understand how these issues with basic functionality keep coming up with every single new Garmin device.

0 Former Member over 7 years ago

I don't know if this is the same issue, but I was getting frequent dropouts in the heart rate reading from Garmin HRM straps. I exchanged the 935 for a new watch. The new one has not show any drop outs in the heart rate reading at all so far.

0 ekutter-dnu over 7 years ago

I don't know if this is the same issue, but I was getting frequent dropouts in the heart rate reading from Garmin HRM straps. I exchanged the 935 for a new watch. The new one has not show any drop outs in the heart rate reading at all so far.

That would be really interesting if the dropout issue is device specific. With numerous people complaining about dropout's on the Fenix but not when they switch to the 935, maybe it isn't just a Fenix vs 935 issue, but an individual unit issue.

In the case of the kickr, it does seems like there is some interaction specific to the kickr causing the problems.

0 Former Member over 7 years ago

I suspect the problem I had was device specific. I was able to run with a 935 and an F3HR at the same time on several runs. Only the 935 showed dropouts in the HR readings (both watches were paired to the same Garmin HRM strap with a fresh battery in it). The new 935 shows good HR readings, exactly like the F3HR has always done.