The HP Model 10544A Quartz Crystal Oscillator is an extremely stable, compact, low-power source of 10 MHz. Fast warm-up and a low aging-rate are important for both instrument and systems applications. This is achieved using a new crystal design ruggedly mounted in a cold-welded enclosure. The crystal, along with the oscillator, buffer amplifier, and oven control circuits are all mounted inside a thermally insulated oven. A significant improvement in signal-to-single-sideband phase-noise ratio has been accomplished by oscillator circuit modifications. This performance along with the excellent short-term stability of the 10544A make it an ideal oscillator for use in systems where the crystal output is multiplied to a higher frequency. Model 10544A is designed to mate with standard 15-pin printed circuit board connectors which permit direct connections and eliminates the need for separate sockets and interwiring. The unit is designed to operate into a 1000 ohm load. This satisfies most solid-state input requirements. Its unique design features, plus production efficiencies enable HP to offer, inexpensively in the 10544A, the better than 5 x 10–¹⁰/day aging formerly available only in expensive laboratory-type oscillators. With this low aging rate of less than 1 x 10-⁷/year the manufacturer of communication and test equipment can offer his customers a real cost saving by reducing the frequency of calibration necessary to stay within FCC accuracy requirements. The 10544A is ideally suited for use in communication and navigation systems, synthesizers, time-code generators, counters, and spectrum analyzers. The 10 MHz output frequency is a convenient starting point since it is easily divided or multiplied. A screwdriver adjustment through the top of the oven permits frequency adjustment over a range of more than 2x10-⁶ (20 Hz), yet the control is sensitive enough to allow adjustment to better than 1x10-⁹ (0.01 Hz). Frequency can also be controlled electronically over a 1 Hz range with an externally applied voltage.