It's not really a hobby project, UHF construction is extremely critical, which is why you're not likely to find many designs. You also have licencing problems, it's a fairly serious offence in most countries to use an unlicenced transmitter.
These modules are generally on frequencies that do not require an license for operation and as a result have limited range.
Having built many rf transmitters I agree with Nigel.
One of the problems with free running oscillators at UHF frequencies is the stability of the oscillation frequency. On method is crystal control at a lower frequency and then multplying the frequency a number of times to reach the UHF frequency. Another method is to SAW resonators, which I think the modules provided by the above websites may very well use.