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564tcxo [2007/04/18 21:36]
564tcxo [2007/05/21 00:43] (current)
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-====== ​TCXO Installed in Omni VI Plus? ======+====== Omni VI+ TCXO Information ​======
 **From the Ten-Tec Reflector January 19, 2005** **From the Ten-Tec Reflector January 19, 2005**
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 Scott Robbins\\ ​ Scott Robbins\\ ​
 +**January 20, 2005**
 +The recent discussions on the reflector regarding Temperature Compensated Crystal Oscillator (TCXO) versus Oven Controlled Crystal Oscillator (OCXO) in the OMNI-VI (retrofitted) and VI+ (retrofitted or production) seem to be void of an understanding of the merits of each.  First is a general comparison of TCXO and OCXO oscillators based upon frequency stability versus temperature:​
 +  -A TCXO contains circuitry in which the output from an ambient temperature sensor is used to develop a correction voltage which is applied to a variable reactance in the oscillator circuit to compensate for the crystal'​s frequency variation due to temperature. ​ The temperature compensating components are generally exposed to the local ambient and are chosen to maintain a relatively stable frequency versus temperature curve relative to ambient temperature changes. ​ Typically, analog TCXO's can provide 20-30 times better frequency stability versus temperature than that of a basic crystal oscillator (XO).  A TCXO will also exhibit a temporary frequency drift if the temperature sensing element (usually a thermistor) does not have the same thermal time constant as the crystal and a TCXO's phase noise [can] be inferior to standard XO and OCXO circuit designs. ​ TCXO's generally are used in low power applications,​ when fast warm-up is desirable, and when costs are a significant factor.
 +  -An OCXO, on the other hand, includes all of the temperature sensitive components (including the crystal) within a temperature-stable oven whose temperature is set to maintain a frequency versus temperature curve slope of zero, or nearly so, for the particular crystal cut (SC, AT, etc.) used in the oscillator. ​ The oven temperature is maintained nearly constant at the required crystal design temperature,​ regardless of changes in the ambient temperature. ​ Typically OCXO's exhibit 1000 or more times better frequency stability than the general XO and 50 or more times better frequency stability compared to the TCXO.  Even a low cost OCXO provides better temperature stability than TCXO'​s,​ but at the expense of much greater power consumption,​ typically several watts. ​ The lower cost OCXO's typically use AT-cut crystals which can exhibit a significant thermal transient effect and require considerable time to stabilize at their design operating temperature (sometimes ranging into the hours) while an SC-cut crystal stabilizes as soon as it reaches (or nearly so) it's design operating temperature. ​ Cost is a significant factor!
 +  -The following is a direct comparison of some of the more important parameters of TCXO's and OCXO'​s:​
 +    -Accuracy/​Year:​
 +       *TCXO - 2 x 10exp-6
 +       *OCXO - 1 x 10exp-8
 +    -Aging/​Year:​
 +       *TCXO - 5 x 10exp-7
 +       *OCXO - 5 x 10exp-9
 +    -Stability:
 +       *TCXO - 1 x exp10-9
 +       *OCXO - 1 x exp10-12
 +    -Warm-up time in minutes:
 +       *TCXO - typically < 0.05 minutes
 +       *OCXO - typically < 4 minutes
 +In summary, the OCXO is preferred over the TCXO when long term accuracy, aging, and stability are concerned. ​ If rapid warm-up time is the primary consideration,​ the TCXO is preferable.
 +Cost is probably the major factor to be considered in [manufacturing] when the other factors are relatively insignificant; ​ there is a substantial difference between the cost of TCXO's and OCXO'​s. Typically a TCXO design implementation can range in price from < $10 to around $100 while an OCXO design can start at well over $100 and range up into the thousands of $$!
 +73, Dave, K1FK

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