[time-nuts] AD9832 in FE-5680A
EWKehren at aol.com
EWKehren at aol.com
Sat Nov 12 19:55:43 UTC 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.
Bert
In a message dated 11/12/2011 2:34:06 P.M. Eastern Standard Time,
denwood at orcon.net.nz writes:
Bert,
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?
73,
Murray ZL1BPU
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