[time-nuts] FE-405B Reprogramming

[Logan Cummings]

Thanks Bob,

       I figured if it was that easy someone else would have already done
it. Went looking for a schematic and found Tom's page describing the
architecture at a high level and with ADEV plots providing evidence of said
architecture. Good block diagram from an FEI presentation at the bottom of
the page http://www.leapsecond.com/pages/fe405/

      Takeaway: no, can't be done - 5MHz DOCXO clocks a DDS which outputs
at 15MHz feeds into a PLL steering a standard 15MHz VCXO which then
provides the output directly.

      Very interesting architecture and gives me some food for thought, but
does not solve the 15 != 10 problem Nick was facing.

Cheers and thanks again!
-Logan

On Wed, Jun 8, 2016 at 3:06 PM, Bob Camp <kb8tq at n1k.org> wrote:

> Hi
>
> The 405 appears to have some “bandpass” elements in it. You can not tune
> it over a wide range.
>
> Bob
>
> > On Jun 8, 2016, at 3:08 PM, Logan Cummings <logan.cummings at gmail.com>
> wrote:
> >
> > Hi All,
> >
> >    Nick's request for a divide-by-three circuit to get his FE-405B to
> > output a 10MHz signal got me thinking - didn't want to threadjack.
> >
> >    I had assumed that the FE-405B's DDS output and FE-5680 compatibility
> > made it a good candidate for output frequency reprogramming. Has anyone
> > determined that this is not possible? My biggest concern was that if the
> > internal crystal is also at 10MHz you'd get bad spurs trying to output
> the
> > DDS at the same frequency..
> >
> >    Does anyone know if the FE-405B uses the original FE-5680 DDS circuit
> > or the more recent one that is only narrowly (EFC) tunable over the
> serial
> > interface? Would be great to have a stable reference at 1, 5, 10, etc.
> MHz.
> >
> >
> >     Any info/references on the FE-XXX internals would be appreciated!
> >
> > Thanks,
> > -Logan
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