I’d put one on each end. You want to suppress the errant signal and stop it entering the device(s). In theory one at the receiver would work.

Thanks Radu, that was easy to do after I moved house.
The old place next to the winery had a lot of air pollution during the vintage.
Currently we have bad air because of bushfire smoke across the area, and I hope that my new place shows better values most of the time.

I was confused by this as well, but now understand that the raw data from the sensor needs some manipulation to provide the Air Quality Index. It seems to be an inverse relationship, but also requires the humidity data. Is the formula used for this available?
I have found the datasheet, with the basic instructions, and the python libraries, but am looking for any python code ready for use.