[time-nuts] fast switching quiet synthesizer

[Bob Camp]

Hi

Consider that stepping every ms means settling in much less than that. If you need < 100 us settling, a pair of synthesizers is probably the only way to go. Use some sort of modulator / switch between them to keep the key clicks from driving you nuts. 

Bob

On Oct 7, 2014, at 1:02 PM, Jim Lux <jimlux at earthlink.net> 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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