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The K3EXREF option locks the K3 or K3S reference oscillator frequency to an external 10 MHz source by automatically controlling the REF CAL function. While locked to the external source, the reference oscillator frequency is maintained within 2 Hz.

Since the K3EXREF does not phase lock the reference oscillator, the external 10 MHz source has no impact on the K3’s phase noise performance. For best performance we recommend your K3 or K3S be equipped with the KTCXO3-1 high stability (±1 ppm, ± 0.5 pp m typ.) reference oscillator.


The option consists of one small pc board that mounts on the existing KREF3 board and a cable assembly that brings in the external 10 MHz signal to the board from the K3 or K3S rear panel. No soldering is required to install the K3EXREF option.

External Frequency Reference Input for the K3S Quantity Price
K3EXREF Ext 10MHz Ref Input for K3S, Kit $109.95
K3EXREF-F Ext 10MHz Ref Input for K3S, Factory Installed $109.95