Are RV TPMS sensors operating at 433MHz FCC permissible?

[dosw]

I was looking for TPMS sensors for my trailer. I found the following on Amazon with good reviews: RV TPMS Sensors

 

Something in the product description caught my attention; the sensors transmit at 433.92MHz, which is in the 70cm amateur band.

 

That raises a couple of questions. First, does the FCC allow for these low-powered short-range devices to operate in the 70cm band? I assume that given the fact they last 6 months of run-time on a set of CR2032 batteries, and obviously couldn't have much of an antenna, that they are very short range and unlikely to cause interference at more than 150 feet. Does the FCC allow them to operate in an Amateur band?

 

Second, will they cause interference to me; if I'm monitoring repeaters within the 70cm band, typically a little higher up in the band, would these interfere? I suppose to answer that question one would have to test. The ARRL band plan shows:

433.00-435.00

Auxiliary/repeater links

 

...so if these are well behaved they would not interfere with reception of a repeater itself, since they are usually in the 442-445 and 447-450 range. And the only way to be sure these are well behaved is to test with a spectrum analyzer or SDR. As an example, though, I've found that one of the USBC-to-HDMI dongles I use at my home office causes interference in the 440MHz range when I'm within about 30 feet of it -- enough interference with enough tertiary spikes that some of the 70cm band is unmonitorable to me when I'm too close to this adapter.

[amaff]

Short answer: yes. I don't know what brand you're looking at, but the OEM giant in this space is Continental and:

https://fccid.io/KR5TIS-09DL

[SteveShannon]

Yes, they’re allowed. We share portions of the 70 cm amateur allocation with other users, including TPMS. 

[dosw]

Thanks for the quick responses. 

[amaff]

A quick google shows a handful of instances of interference if you're sitting right on 433 (either the TPMS light on the dash coming on when you transmit, or occasional noise when receiving. At least 1 seems to have fixed it by moving the antenna.

https://kq4afy.xyz/blog/2022/12/tpms-uhf-interference/

https://www.reddit.com/r/amateurradio/comments/1l732o2/today_i_learned/

 

[Lscott]

40 minutes ago, dosw said:

That raises a couple of questions. First, does the FCC allow for these low-powered short-range devices to operate in the 70cm band?

YES. Unfortunately the FCC allows a bunch of other crap to operate there as well.

https://www.ecfr.gov/current/title-47/chapter-I/subchapter-A/part-15/subpart-C/subject-group-ECFR2f2e5828339709e/section-15.240

Some examples:

https://hackaday.com/tag/433-mhz/

[dosw]

1 hour ago, Lscott said:

YES. Unfortunately the FCC allows a bunch of other crap to operate there as well.

https://www.ecfr.gov/current/title-47/chapter-I/subchapter-A/part-15/subpart-C/subject-group-ECFR2f2e5828339709e/section-15.240

Some examples:

https://hackaday.com/tag/433-mhz/

Got it... don't tow the trailer near an airforce base! 

[Lscott]

22 minutes ago, dosw said:

Got it... don't tow the trailer near an airforce base! 

Sounds funny, but it's a real thing. Some Ham 70cm repeaters had to be dialed down in power level to stop interference to Pave-Paw radars.

https://www.arrl.org/news/new-70-cm-coordination-agreement-reached-for-new-england

https://sites.google.com/site/arrlsacvalley/pave-paws