Just good enough 10 MHz reference


Sverre Holm  writes:

Some time ago I noticed that the Ublox Neo-7M GPS has a 10 MHz output which is locked to the GPS system’s accuracy. Most people kept saying how useless it was due to excessive jitter unless it was cleaned up with a phase locked loop of some sort. But at the same time I installed the reference input for my Elecraft K3 (K3EXREF). It enables the K3’s frequency to be locked to an external 10 MHz reference. What struck me was how its function was described:

  • The frequency of the internal oscillator of about 49.38 MHz is continuously measured and averaged, obtaining a value to the nearest 1 Hz.
  • The K3EXREF does not phase lock the K3’s reference oscillator and the external 10 MHz source has no impact on the K3’s phase noise performance.

This got me wondering if the Neo-7M would be just good enough as a reference and that all the averaging internally to the K3 would take care of the jitter.

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1 Comment

  1. How much phase noise / jitter is “acceptable”?
    Say you have a TCXO, driving an si5351 [3 channels output].

    If I tuned one channel of the si5351 to 10MHz, then compared it with the Neo-7M GPS, would that be enough to determine the actual frequency of the TCXO? Would the jitter of the si5351 be “acceptable”?

    I was contemplating something like this, to drive the clock of an AD9851 at 178.956 970 67 MHz [steps of exactly 1/24 Hz]

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