[time-nuts] 10Mhz Sine from Square Wave Synthesizer

WB6BNQ wb6bnq at cox.net
Mon May 20 15:03:17 EDT 2013


Hi Andy,

If it is at 9.8304 MHz, don't even consider trying to fool with anything inside.
While it does have a DDS inside, it is of the newer design where the DDS is
inside the loop that determines frequency for locking the Rubidium.  It requires
a crystal, coil and firmware change to move it to 10 MHz.  Unless you want to
spend some big money, Symmetricom will not help you at all.

How do I know ?  Well, I have one and tried !  Even got the proper crystal sent
to me, but did not get any firmware.  Also there may be a super small surface
mount coil that needs to be changed to make the replacement crystal oscillate.

The 9.8304 MHz is related to various baud rates and also some clocking
frequencies for sound cards.  So, don't throw it away as it is still useful.  If
nothing else you could phase lock a 10 MHz oscillator to it as there is a
connecting ratio.

Bill....WB6BNQ


Andy Bardagjy wrote:

> Alright, so it seems that it's possible the Symmetricom SA.22c that I've
> got might be set to 9.8304MHz. That may be programmable to 10MHz, but it
> might require a DDS otherwise.
>
> Nevertheless, if the oscillator is set to 10MHz it seems the consensus is
> to construct a LPF.
>
> Luciano, thank you for sharing your design, did you wind your own
> inductors? Odd values.. Typically when designing filters I start  by fixing
> the inductor values and work backwards...
>
> John, thanks for your input, you reminded me that LFP performance often
> depends on source impedance. To the MMIC amplifier, you'd be amazed what
> you can do with an opamp these days. I was amazed reading the datasheet for
> the LTC6409 a 10GHz GBW, 1.1nV/sqrt(hz) fully differential opamp. With a
> gain of one, the frequency response is totally flat out to 1GHz.
>
> http://cds.linear.com/docs/en/datasheet/6409fa.pdf
>
> Perhaps something like a LT6600-15 might be a complete solution for me -
> it's a fully differential amplifier with a 15Mhz 4 pole LPF.
>
> http://www.linear.com/product/LT6600-15
>
> Thanks for your input, I'll be sure to keep everyone posted on my project's
> progress.
>
> Andy Bardagjy
> bardagjy.com
>
> On Mon, May 20, 2013 at 12:03 PM, Luciano Paramithiotti <timeok.it at gmail.com
> > wrote:
>
> > Hi Andy,
> >
> > The simplest way is to use a low pass filter with a notch capability for
> > the second and third harmonics.
> > You can find the schematic and response for 5 and 10 MHz here:
> >
> >  http://www.timeok.it/files/5_and_10mhz_low_pass_notch_filter.pdf
> >
> > ciao,
> >
> > Luciano
> > timeok
> >
> > see: www.timeok.it
> >
> > On Mon, May 20, 2013 at 1:30 AM, Andy Bardagjy <andy at bardagjy.com> wrote:
> >
> > > Hi folks, I recently picked up a Symmetricom SA.22c rubidium oscillator.
> > > According to the datasheet, it outputs a square wave with programmable
> > > frequency (well you can pick among some set of frequencies).
> > >
> > > I'd like to build up a small circuit locked to the square wave output
> > which
> > > outputs a 10MHz sine wave for use as my "house clock" for my various
> > > instruments (spec an, counter etc). I of course could distribute the
> > square
> > > wave, but am concerned about harmonics, among other things.
> > >
> > > The FE-5680A uses a AD9830A DDS to synthesize its output. Is a DDS the
> > > right way to go - in terms of performance, phase noise and so on?
> > >
> > > I suppose I could do this with a tank or some other analog circuit, but..
> > >
> > > Andy Bardagjy
> > > bardagjy.com
> > > _______________________________________________
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> > >
> >
> >
> >
> > --
> > Luciano
> > Timeok
> > visit : www.timeok.it
> > _______________________________________________
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