Aeotec Z-Stick Gen 5 -- Cellular Interference

Back in September I purchased an Aeotec Z-Stick Gen 5 and have been using it since with my Pi and HA… Tonight I just had a tech from AT&T come by stating that he’s been troubleshooting some interference with their cellular towers and had pinpointed it to our house. After some discussion I had mentioned I have some home automation with ZigBee and Z-Wave devices. He then showed me a picture of a Z-Stick from another trouble ticket he was working - which was the same device as mine.

We did various testing – unplugging the stick cleared the interference (which was interfering with the 710.337 MHz band on their tower). Plugging it back in, the interference resumed. Pointing his scanning antenna directly at the device, his scans lit up. I was given a letter explaining the FCC violation and asked to unplug the device (which I have done) - and then asked Amazon for a refund (which they agreed to even tho I’m past the return window).

With all this said:

  1. Has ANYONE had this issue with this stick before?
  2. What other stick should I use?

No Z-wave device should even be transmitting with that as the fundamental frequency, though I suppose it could be a spur or harmonic? Sounds like a defective stick to be honest. I would reach out to the manufacturer before amazon, perhaps they are aware of a bad batch of devices that got shipped.

I did both - just finished creating a ticket with Aeotec as well. The ATT tech was mentioning it being a harmonic potential issue too after I mentioned the stick should be running at 900 MHz range.

I had the exact same thing happen here, too. The Z-Stick was erroneously broadcasting at 712.456 Mhz.

AoTec took care of me with no issues at all. Give them a buzz/support ticket.

Did Aeotec give you any more information about what exactly was wrong with the stick ?

This is super strange. No harmonic should ever be strong enough to interfere with a cell tower, by orders of magnitude (and 700-something MHz isn’t even a harmonic of 900MHz). Did the center frequency of your stick change ? Did it still work as your zwave controller while in this state ? Was it connected to a USB3 port ?

@rbdixon, how did you know it broadcasted at 712.456 MHz ? Did you hook it up to a spectrum analyzer ? And same question as above, did your zwave network still work with the stick ?

I had mine connected to my raspberry Pi3+ and it was working fine from my perspective. No issues. This was the response I got back from support after they diagnosed my stick (again I was overly impressed with their support and replacement unit through this process.)

From support:
the determined issue is a defective saw filter causing it to operate at the wrong frequency. Have you come across any issues with the unit that I sent to you?

Interesting. Very surprising that it still worked on the zwave network (so it still transmitted at least some signal at 900MHz), while sending out enough spurious RF energy to interfere with the cell signal.

Thanks for the info !

I mean, maybe that issue is more widespread than one may think. Most people would probably never notice it, but it would probably affect the maximum range of your zwave network quite a bit.

My thought is that the saw filter should exclude all but the 900 Mhz range and being bad signal was leaking into the 700 range… Not sure if that would effect the range of it’s a ZWave or not honestly… And yeah - most people would probably never see any issue like this, it’s the combination of mine being bad AND also being within a quarter mile of a cell tower.

I’m about 600 feet from the tower. I had a chance to observe the device radiating on the portable RF spectrum analyzer the technician was using. A very nice R&S PR100 portable receiver… eBay says they cost $20k! The center frequency was 712.456 Mhz.

The Z-Stick was working ok but I was having issues controlling some nodes. I moved recently and I had not gotten around to investigating any of that.

Hah. Very nice. Yeah the tech that showed up at my door let me see his device as well. Was rather cool (being techie) to see that equipment and how he was triangulating it all.