Ask Dr. SETI ®
Dear Dr. SETI:
The Doctor Responds:
Steve at DEM sells the PTC thermistors (60 ohms @ room temperature) for something like a buck. The unit functions as a poor man's crystal oven, thus: The thermistor draws current, and heats up (also heating the crystal can). Its resistance goes up, so it draws less current, and cools down somewhat. Now R goes down, the PTC draws more current, heats up, and so on, eventually reaching thermal equilibrium at about 30 Celsius degrees above room temperature. So what you have is a self regulating proportional temperature controller.
The long term solution will eventually be for each Project Argus participant to use a GPS-disciplined master frequency standard. This will give everybody nearly atomic-clock accuracy, and precise time calibration to boot. But for now, a $1 PTC thermistor will give you an order of magnitude improvement in frequency stability, as compared to running a crystal LO at room temperature.
entire website copyright © The SETI League, Inc.
this page last updated 28 December 2002
Top of Page