[time-nuts] FE-5650A option 58 tuning word for 10 MHz output

[Mathias Weyland]

On 2017-01-02 01:31, wb6bnq wrote:

Hello Bill

Thanks for your response and the pdf manual. There's lots of good
information in there. You are certainly right in that there's a
few things that I have not understood. Unfortunately this has not
changed after having read your response:


>  That "R" number is actually the Rb frequency divided by 136 plus the
> upward fine tuning of the C-field pot.  See PDF page 16 & 17 of the
> attached PDF operational manual for the FEI-5650.

In the comprehensive post[*] that I quote in my original request,
Mark states that "THE R= REFERENCE FREQUENCY IS NOT THE FREQUENCY
THAT THE  PHYSICS PACKAGE IS SHIPPED TUNED TO!!!  It is the
frequency produced by the  physics package at the minimum setting
of the C-field potentiometer."

This seems to be contradictory to what you wrote. Either the R value
is determined at the C-field pot minimum frequency position as Mark
stated, in which case it does not contain the upward C-field
tweaking. Or it is determined after the final tweaking as you say.
Either way I don't understand how to incorporate the R reference
frequency into my calculations, which is what Mark seems to be
suggesting.


>  The "F" number is truly a 32 bit number, not just the first 8 digits
> but all 16 of them.

The F number has 16 hex digits. Since each of those digits represents
a nibble (i.e. half a byte, 4 bits), I end up with 16*4 = 64 bits. Not
just 32. The first 8 digits of the F number however represent a 32 bit
number, which is also the size of the the phase accumulator in the
AD9830 which makes sense in my opinion. I think I absolutely failed
to grasp what you're trying to tell me here :-(

Re-reading the paragraph in [*] that starts with "You can set the
divisor" did clear up something for me though -- looks like there's
nothing weird with the F-number stored in my unit; the last byte is
indeed 0x00. I still don't quite understand why this parameter is
potentially stored at a higher precision than what the DDS can
deliver.


>  It would probably have been better to purchase one of the Rb's that
> already output 10 MHz instead of hacking the option 58.  BUT that is
> just my opinion.

You are probably right on that, yet getting any of those surplus
standards off of ebay seems to be a bit of a hit-or-miss thing
anyway. At least I get the learning experience, that's gotta count
for something :-).

Thanks again for your response and best regards

Matt