After visiting ModelExpo exhibition (their website is in Finnish) here in Helsinki in around the mid 2000s, I really got interested in RC airplanes. I mean, I had visited ModelExpo already in the early 90s as a kid, and for a while I tried to get my parents to buy me an RC plane, but they didn't and the whole idea soon died out. This time, however, after exploring the different possibilities I came to the conclusion that as a student I just couldn't afford a hobby so expensive. One of the main problems was the radio system. I didn't want to just buy a 4 channel "cheap" transmitter, because I knew I'd definitely want to update it sometime in the future. Still, even the 4 channel ones were quite expensive as the 2.4GHz revolution hadn't yet really taken off.
I'd already been a keen electronics hobbyist for quite many years back then, so I decided that building my own RC radios was no big deal. For a couple of years, I would play around every now and then with home made 27 MHz transmitters and super-regenerative receivers, but I never really got them to work reliably. While practically given up on my goal, I happened to stumble across a company called HopeRF, and especially their radio module RFM12, which was used in quite many small wireless microcontroller projects. After looking for a supplier for these modules, I found Octamex in Germany, which also sold the modules RFM22B and RFM23B at only a marginally more expensive price. After reading the datasheets, it was a no-brainer: the RFM22/23 were much more advanced, so I ordered a couple for operation at 868MHz without ever looking back at RFM12. (For reference: this was around Christmas time in 2010).
It turned out the modules were based on Silicon Labs Si4430 family of EZRadioPRO UHF ICs. The datasheets provided by HopeRF ended up being just badly copied versions of the original Silabs documents. Within just a week or two, I got the modules talking to microcontrollers (which I think were Atmel ATtiny2313) and talking to each other over the air. As I usually can't really keep focused on just one thing for a long time, I decided to first pursue other projects I could use the radio modules with, including home automation and remote sensing. I continued with the RC stuff the following summer.