Indoor ANT+ interference

William Jenks

Full disclosure: I posted this on the Wattage list, too... since there are so many dedicated junkies on power topics there.

All winter and spring I have been training in the same room when riding indoors.  My bike is equipped with a Garmin speed/cadence sensor and a PT wheel (both ANT+).  I have both a Garmin 705 dedicated bike computer and a 910xt multisport watch...i.e., two transmitters and two receivers.

In the last few weeks, we've had lots of thunderstorm activity, so I've had to do some of my riding indoors again.  I have had several occasions in which I get dropouts of several seconds up to a couple minute's duration where I don't get data from either the speed/cadence sensor or the PT wheel.  I have verified that the dropouts are occurring simultaneously on both receivers (705 and 910).  The dropouts are not quite coincident, i.e., not EXACTLY the same times for the speed/cadence and PT, but they have a pretty good correlation.  I doubted that batteries were the issue, but I replaced the batteries in both the PT and speed/cadence sensor.  This did not change the situation.  I have verified that as soon as I go outdoors, all is well again...and then the problem comes back indoors.

My conclusion is that there is probably something in my house that is newly causing some kind of interference.  I understand that ANT+ operates at 2.4 GHz, which is pretty common for other wireless devices, too.  (The bike computers are on the bike...not sitting right next to some other device.)  On the other hand, it could be some random electronic noise from a device not specifically operating at that frequency...e.g., it might sound stupid, but my sump pumps weren't doing anything over the winter, but they are chugging away if I'm riding indoors now.

I am hoping someone can help me narrow the search (or make some other useful suggestion).  What should I be looking for in troubleshooting this?  or do you think I am entirely off base?

Thanks!

tgarson

Interesting. 2.4 Ghz is indeed a very busy spectrum, shared by your wireless router, and less commonly known, by your microwave.

I had a problem with indoor dropouts but it was my computer (trainer road) rather than on my bike computers. That problem was easily solved by plugging my ANT receiver into a USB hub that was located much closer to my bike, since ANT+ is after all a low-power, short-range protocol.

Now your wrist and stem are decidedly within the range and should not be experiencing dropouts, and the correlation with losing both sets of sensors seems to rule out the obvious 'check your batteries' comment.

Unfortunately, don't really know what else to point to beyond that, but I'd be very surprised if it was EMI from something like a sump pump. The microwave seems random, but as you likely know it cooks food with radio waves so it's a lot different than other household appliances.

bmr94539

Yes, ANT+ is in the widely used 2.4GHz band. Sharing that space with your ANT+ devices in your house would be your microwave and probably most of your computers running WiFi. You might also have some portable telephones and/or baby monitors also in that band (or your neighbors might). If you have a smart power meter you might also have ZigBee running on that also in the same band communicating to your local power company's equipment.

In addition, it's possible that you have more RF reflective surfaces in your ride area that could cause the ANT+ devices to interfere with each other indoors even if they don't outdoors. Do you have any large metal objects in the room?

Do you have a smartphone? Is that doing something interesting indoors while you're riding?

It is weird that the dropouts are coincident on both devices and last so long. Are the sump pumps running during that time? it is possible for motors to put out a lot of EMI and ANT+ is a low power protocol so the signal levels to jam it don't have to be particularly high.

Given that the devices work outdoors and don't interfere with each other, I'd be looking for interferers. Some WiFi computers will tell you about in-band interference.

William Jenks

@Trevor... chemists are among the few "civilians" that know about microwaves...water is the bane of microwave spectroscopies (e.g., epr, if that means anything to you). X-band, K-band, Q-band, klystrons, magetrons...... :-) But that's a good suggestion... however, i would assume it would mean that my microwave is "leaking" and I'd have to replace it... so I hope it's wrong! But it could easily be that the time of day varied, and people were using the microwave during the recent workouts and not so much during the winter ones...hadn't thought of that until now. The intermittency and recentness was what made me think of the sumps, but I have no idea whether they could be putting out some kind of EMF like that...I learned that I should be able to test with an AM radio.

The other thing that rules out "range" is that it doesn't happen outdoors.

It's also possible that one of the several normal 2.4 GHz devices in the house has just gone on the fritz.

Hope to have time to investigate this weekend! I'll let you know what I find!

William Jenks

And the verdict is....

... the sump pump. Or at least so it would seem.

We have two sump pumps. Unplugging one of them, I couldn't reproduce the dropouts. With it plugged in and occasionally chugging away, the dropouts started again. Not a perfect correlation, but there were no dropouts when it was off. The microwave did not cause any problems.

For now I am going with this. If I have any more indoor rides in the near future, I'll unplug the sump and see if that takes care of it!

MattAaronson

Funny, I never had indoor dropouts until really recently. Same problem. The microwave has always been an issue but there is somethign else in my house impacting the datastream.