[time-nuts] fast switching quiet synthesizer

Magnus Danielson magnus at rubidium.dyndns.org
Tue Oct 7 13:32:16 EDT 2014


You should be able to use DDS test-boards and by timing your last write, 
you should be able to time the frequency jump.

The STEL-1173 takes 6 bytes, but writing the last one latches all 6 
bytes over to a single 48 bit word. I expect that other DDSes have the 
same distinct transfer-phase if you only look in the datasheet for the 
details.

Some of the modern DDSes can take 10 MHz directly and step it up 
internally before hitting the DDS core, but it may be that you need to 
synthesize a higher clock from the 10 MHz first.

Cheers,
Magnus

On 10/07/2014 07:02 PM, Jim Lux wrote:
>
> At work, I'm putting together a multichannel stepped frequency CW radar
> breadboard, and I'm looking for something to serve as a source that I
> can step quickly.
> I'm looking at stepping every millisecond or so.  Right now, I use a
> Ardunino type microcontroller driving a serial DAC driving a VCO, but
> that's a bit wonky and noisy, although it's easy to get the step timing
> right on.  The spectral purity is, shall we say, downright ugly.
>
> Since I'm going to be doing precision ranging with this, the spectral
> purity has to be reasonably good (not 1E-15 at 1000 seconds good,
> fortunately)..
>
> I was thinking about a PTS synthesizers  (beloved of time-nuts for all
> kinds of reason), and they're nice because they are quiet, and switch
> really fast (microseconds).  However, they all seem to have BCD or GPIB
> interfaces (only).  Sure, I can code up something on an Arduino or other
> microcontroller to drive the BCD on the PTS, but maybe there's something
> else out there that might work as well?  And is already off the shelf.
>
>
> I could hook a Prologix on the back of a PTS with GPIB, and hit it over
> the ethernet, but I'm not sure I'd be able to get the steps to occur
> when I want them (ethernet and determinism do not go well together).
>
> Maybe some DDS in a box product?  That will take my nice clean 10 MHz
> reference?
>
> Ultimately, I'm looking at output frequencies in single digit GHz, but
> something that can be mixed/multiplied up will work just fine.
>
> I'm looking for something that is off the shelf-ey as much as possible.
> Using surplus gear is ok, because I really only need 3 or 4 channels and
> that might be scroungeable, but spending hours wiring up weird adapters
> or locating connectors that haven't been made since 1943 is something
> I'd like to avoid.
>
>
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