Hi Scott, On 04/12/2017 11:38 PM, Scott Stobbe wrote: > Hello, > > I wanted to see if I could soft-start a used OCXO (Trimble 34310) during > warm-up. By default with an appropriately rated 12 VDC supply, the OCXO > starts the heater at about 8 W, and eventually settles down to 2 W for > 20-25 degC ambient temperature. Figure Attached. > > The good news is it does startup with either a current limited or power > limited supply. Albeit, for the constant current case the start-up time is > dramatically longer. Figures Attached. > > The bad news, but interesting tangent is that when this particular OCXO is > soft-started, it doesn't oscillate at 10 MHz! It starts up on a spurious > overtone at 10.9 MHz. There isn't even a hint of 10 MHz in the output > spectrum just the 10.9 MHz tone (and some noise from the banana clip-leads > loop-antenna). So this is a bit of a pain for soft-starting because, > although the oven eventually comes into regulation, the oscillator is > running on the wrong frequency. > > I'm not sure what the tempCo of the 10.9 MHz crystal mode is, but its a > pretty great temperature probe of the crystal (literally). You can see the > sinusoidal frequency disturbance of this tone has the same periodicity as > that of the heater current (~50 s). So I don't know if the heater is > oscillating at the uK level or mK level, will need to find out the tempCo > of this crystal mode. Neat to see the oven dynamics. > > Hopefully once the oven is settled at temp, I can load switch the OCXO for > 10 or 100 ms and get it to startup on the correct 10 MHz mode. With a 10+ W > rated supply it starts up on 10 MHz every time. You should be able to do that. I was just about to propose it. A short power off will still remain the oven temperature, but will re-set the oscillator. Cheers, Magnus