I want to read and send 40.6835MHz signals with an Arduino. Has someone done it before?
Do you mean 40.685MHz garage door opener? If so get a garage door sender and receiver
and hack into them?
My first idea was to buy a send receive kit for 433MHz and switch the crystal to a 40.6835 one on the sending unit. Do you think that's possible?
Not in the slightest, completely different band, radio circuits are narrow-band tuned circuits that have a
small amount of frequency flexibility only. Not to mention the SAW filter.
The second problem is then, how to receive the packages.
There's always SDR of course...