Total posts : 45366
I did an experiment with a BA1404 based transmitter with an LC controlled oscillator. There was no temperature control of the circuit but it was in a stable 72 degree F environment. From “cold startup” the initial drift was +23 kHz. After thermal equilibrium with the enviornment was achieved after several hours of power on the drift was observed to be +/- 7 kHz, the cause of which I never determined. I will mention that the 1404 output was buffered from the antenna since lack of buffering can cause frequency pull.
A space heater was used to raise the environment to 76 degrees F and the drift was +20 kHz. I did not pursue this any further after concluding this was not acceptable for my intended use.
Your results with the FM-10C may differ and you may be able to stabilize it to your satisfaction and that is fine. I decided it was easier to purchase the FM-25 and be done with it. My FM-25 is in an environment where the ambient varies from 70 to 78 degrees F and the maximum drift in output frequency (checked about every three months) is 400 Hz at 90.9 MHz. Since this is very small I never bothered to try to correlate this with temperature.