Sulzer 2.5C quartz oscillator


The Sulzer 2.5C is a very high-quality double oven 2.5 MHz AT-cut crystal frequency standard from the early 1960's. It is exceptional even by today's standards, easily outperforming modern OCXO such as the HP 10811A in stability and frequency drift.

Short-term stability of parts in 10-13 and drift rates of parts in 10-11 per day are not uncommon. The oscillator electronics included dividers producing 1 MHz and 100 kHz outputs in addition to the primary 2.5 MHz output (or should we say 2.5 Mc ;-). See Sulzer 2.5B and 2.5C schematic for details. Also available in wide version.

After 30 to 40 years (were the 60's that long ago!) some old Sulzer oscillators either no longer work or they have excessive phase noise or frequency instability (e.g., the proportional oven circuits have problems). The one below appears to have survived the years very well.

Photo Gallery

Measured Performance Summary (see below or click to enlarge images)

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Oscillator Short-term Performance (large images)

The four stability plots were obtained with a TSC 5110A Time Interval Analyzer frequency stability measurement system and a homebrew scheme to produce online webcopy images rather than printer hardcopy plots. With 0.1 picosecond (100 fs) resolution and an embedded PC the 5110A calculates and displays auto-scaled log-log Allan Deviation plots in real-time for tau as short as 0.01 second and as long as you are patient. The noise floor of the 5110A is on the order of 10-17 and a Hydrogen Maser was used for the reference channel so the measurement system is typically orders of magnitude more stable than the unit under test. Thus for all tau up to a day or week the plots below can be assumed to be absolute rather than relative to the reference oscillator.

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Oscillator Long-term Performance

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Page last modified 21-July-2001.