@Russ I'll get it together over the weekend, but essentially the RPITX project provided most of the answers for me https://github.com/F5OEO/rpitx it's a bit of a cludge as it uses a short wire on a Pi GPIO pin to TX, but it works just fine. I've also got a HackRF One, which was really useful for capturing and decoding the signal from the gate remote, but with a cheap RTL-SDR dongle you can do that with RPITX as well. I've even seen people getting stuff like rolljamming working with the Pi - which has been in the news in the UK as the basis of replay attacks used by car thieves. Radio was a whole new world to me and I have to say that after a few intense weeks of getting various projects built, I still feel like I know next to nothing :-). Main thing I learned - the right type of antenna for the application is crucial. Anyway, I'll waffle on about it in the forum but please don't hesitate to get in touch if I can help.
Ade