[time-nuts] AD9832 in FE-5680A

EWKehren at aol.com EWKehren at aol.com
Sat Nov 12 14:55:43 EST 2011

I did measure the Xtal and it is 60 MHz. That is the only thing I know for  
sure. I did not probe the output of the DDS because with my 69 years old 
hands I  do not want to slip and destroy the unit, some one else may want to 
test it. As  a group we should be able to solve the problem since the prices 
are free  falling. Sooner than later every time nut will have one.
In a message dated 11/12/2011 2:34:06 P.M. Eastern Standard Time,  
denwood at orcon.net.nz writes:

Your comment about the AD9832 being a 25MHz part made me  think, and I too 
wonder how it might all work. The data sheet calls it a 25MHz  part, and I 
agree with you that it might be expected that some extra division  occurred 
between the ~60MHz Rb loop and the synthesizer MCLK.

That's  not the case however. I don't know how it's achieved, but the 
FE-5650A and  FE-5680A (the versions with AD9832 and user-programmability, I 
mean) do in  fact appear to operate with a ~60MHz MCLK. I support that statement 
with two  facts:

1. The AD9832 in these models is capable of generating  moderately good 
12MHz output, which it certainly would not with a 25MHz  MCLK.
2. The frequency calculations used give you a step size of about  10mHz, 
and as you will realize, 50MHz/2^32 is about 10mHz. I've used the  ~50MHz 
figure (actually either 50.255MHz or 60MHz) in my software.

Does  anyone know how we can resolve this apparent  inconsistency?

Murray  ZL1BPU
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