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

Scott Stobbe scott.j.stobbe at gmail.com
Mon Jan 9 12:48:09 EST 2017


It very well could be. Based on Marks comments, it sounds like the DDS tone
after being squared up is directly driving a 23-bit counter for the 1 PPS
output.

On Mon, Jan 9, 2017 at 12:17 PM, Bob kb8tq <kb8tq at n1k.org> wrote:

> Hi
>
> In most Rb’s (including the FE 56xx’s) the DDS is mixed with a fixed
> microwave
> frequency signal. The DDS only has to make up “part” of the total offset.
> You get
> roughly a three orders of magnitude improvement because of this. Rick has
> gone
> into all the gory details of why it gets done this way in talking about
> the 5071. It
> is the same thing on an Rb.
>
> So, your basic math is correct about a normal DDS. In this case you are in
> the
> PPT rather than PPB range due to the multiplication.
>
> Bob
>
>
> > On Jan 9, 2017, at 10:40 AM, Scott Stobbe <scott.j.stobbe at gmail.com>
> wrote:
> >
> > A 32-bit DDS synthesizing at 1/5 Fs, yields a tuning resolution of ~ 1
> ppb.
> > So, I would imagine a slightly lower frequency is programmed into the DDS
> > and the c-field is trimmed to yield a higher precision. If the new
> > synthesized tone you wish to generate is an integer number of DDS codes
> you
> > could start by assuming the c-field is trimmed to be on frequency, but if
> > the new tone is a fractional number of 32-bit DDS codes you will have to
> > manually trim if you want higher precision.
> >
> > On Mon, Jan 9, 2017 at 4:48 AM, wb6bnq <wb6bnq at cox.net> wrote:
> >
>
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