M1GEO's blog, found https://www.george-smart.co.uk/projects/lnb-bias-tee/ when looking for bias tees.
Another air quality sensor is described on https://www.george-smart.co.uk/2021/02/an-esp8266-based-air-quality-sensor/

Found via the author's blog https://www.dl1ye.com/posts/2021-04-29-universal-lnb-biastee/ which in turn was found when searching for a bias tee.