[time-nuts] GPSDO and oscillator steering - EFC vs DDS schemes?

[Poul-Henning Kamp]

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In message <56675DA0.4050609 at rubidium.dyndns.org>, Magnus Danielson writes:

>> So, what did I miss? Why do people use DAC-EFC control instead of
>> the DDS scheme?
>
>The main reason I would say is habbits, people have habbits and stick to 
>them.

And I think right after that comes the problem of spurs.

Controlling DDS spurs is mostly a solved problem, when you get to choose
your input and output frequencies for that purpose.

But as "afterburner" for an OCXO, there is no restriction on the two
frequencies, and they are almost guaranteed to be close-in multiples,
so coping with the spurs becomes non-trivial.

That basically means that you need 50% higher DDS and DAC resolution
than everybody else in the market an suddenly it isn't cheap any more.


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