[time-nuts] Aging 5065A ?

[Hal Murray]

kb8tq at n1k.org 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.