Application Notes

Stratum 3 and Stratum 3E oscillators have two frequency stability specifications (Free Run and Holdover). Bellcore has somewhat defined a third requirement, Drift. The Drift requirement is not per say a Bellcore specification. However Bellcore suggests that the Drift be used for calculating the Holdover specification and suggests Drift values.

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Loads for Rectangular Waveforms Specified…

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This paper explains some of the information on ISOTEMP Temperature performance print out.

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1. Levels

“0″ Level: The average voltage of the low part of the waveform.
This voltage level is measured with respect to ground (0 VDC).

“1″ Level: The average voltage of the high part of the waveform.
This voltage level is measured with respect to ground.

Note: This voltage level is sometimes referenced to the input voltage (Vcc).

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The purpose of this application note is to explain what Cp and Cpk are and how these statistical tools can be used to prevent shipping marginal products. Most people have at least heard of Cp or Cpk, but few people really understand the concepts behind the calculations. This is valuable information not just for Quality Managers, but also for the Engineers who design new products, as well as Purchasing Agents who have to maintain a list of qualified vendors. In fact the 1994 revision of ISO 9000 requires suppliers to evaluate their subcontractors on the basis of their ability to meet subcontract requirements (Section 4.6.2).

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The purpose of this application note is to explain what Cp and Cpk are and how these statistical tools can be used to prevent shipping marginal products. Most people have at least heard of Cp or Cpk, but few people really understand the concepts behind the calculations. This is valuable information not just for Quality Managers, but also for the Engineers who design new products, as well as Purchasing Agents who have to maintain a list of qualified vendors. In fact the 1994 revision of ISO 9000 requires suppliers to evaluate their subcontractors on the basis of their ability to meet subcontract requirements (Section 4.6.2).

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With today’s increasingly crowded communications spectrum, the need for high performance frequency references is increasing. High stability test equipment also calls for superior time bases. The ovenized oscillator is an attractive answer to these and other applications requiring a high performance to cost relationship. The ovenized oscillator is more complicated than first glance might suggest, however. This paper explains some of the subtleties of ovenized oscillators, so they may be more fully understood and specified.

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Normally, when trying to determine how tightly grouped a set of data is, the standard deviation (s, or square root of variance, s2) of that data is calculated. However, when making this calculation on a group of frequency measurements taken from an oscillator, long term stability variables (such as aging and ambient effects) can begin to obscure the short term stability of that oscillator. In this instance a calculation called Allan variance (named after David Allan of NIST) provides better results. Simply put, instead of calculating the variance for an entire set of data at once, the variances from progressing pairs of data points are averaged, minimizing non-short term factors.

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Isotemp Research, Inc. is producing high quality frequency control products for the communication and test equipment industry. The company was founded in 1968 and has provided continuous growth and product improvement through value engineer and surface mount production techniques. The Current product lines include Oven Controlled Crystal Oscillators (OCXO’s), Temperature Compensated Crystal Oscillators (TCXO’s), and miniature heater for quartz resonators. Crystal oscillator products are usually designed to meet specific individual requirements for size, output frequency, input voltage, output power, stability, and many other parameters.

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This technical note is to help customers specify aging of crystal oscillators. Long term frequency drift is an important characteristic of crystal oscillators and is specified by an aging requirement. If the nature of aging is not understood, aging requirements may be improperly specified. The modeling presented here has been used by ISOTEMP RESEARCH, INC. for many years and concurs with MIL-0-55310B.

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