Hi Well….. the existing synth in the 5065 is no champion spur wise. Coming up with a DDS that is “as good as” is not all that crazy.
The 5 MHz reference is multiplied to 6.x GHz and then mixed with the synth. The close in phase noise of the multiplied signal is mixed with the synth. The output is the sum of the two. Going from 5 MHz to 6.x GHz gets you 20 log (N) … a bit over 60 db added phase noise. The synth (at 100 ti 300 Hz offset) needs to be 60 db worse than the noise on the 5 MHz before it even gets in the game. That’s not a really tough spec to meet. Bob > On Oct 7, 2020, at 6:18 PM, Hal Murray <[email protected]> wrote: > > > [email protected] said: >> If you want to run a fixed / well regulated C Field, a DDS with (say) 48 bits >> would allow you to tune the device well past parts in 10^-15. > > I don't know how to think about a DDS in this context. > > I remember years ago thinking that a DDS was the greatest thing since sliced > bread. In the context of something like a PPS going into a PC for > timekeeping, that's probably true. You get long term accuracy and the PC > can't see the short term issues. > > But then, somebody mentioned close-in spurs. They get closer the more bits > you have in the DDS magic number. (What is that number called?) > > > Suppose I have a black box labeled "10 MHz" with a cable coming out. > > If you plug that cable into your ADEV measuring setup, can you tell if my box > has a DDS in it? > > If you plug that cable into your spectrum analyzer, how good a setup do you > need in order to see the spurs? Do they get lost in the close in noise? Or > maybe the question should be how clean a signal do I need to start with > before > the spurs become visible? Or what should I be asking? > > > -- > These are my opinions. I hate spam. > > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
