Hey,
I've managed to decode the RF signals from the new SL-109H. There's also a really bizarre coincidence here.
I just recently figured out the RF signal encoding for the AcuRite 00955 sensor -- a co-worker had one and was interested and so I worked that out (there's already info on the internet about that one too).
Then, by total random coincidence I saw the SL-109H advertised and bought one to look at the signals. Guess what -- these RF signals are kissin' cousins. And the SL-109H signals are unlike any of the OS protocol versions 1.0, 2.1 or 3.0. I wonder if there is some business connection between OS and AcuRite?
Anyway, I've added this info to a PDF document which you can download at the link below if you're into that sort of thing (yeah, I know...very limited set of folks there, but someone may have an interest).
http://www.osengr.org/WxShield/Downloads/OregonScientific-RF-Protocols-II.pdfCheers!
