[time-nuts] fast switching quiet synthesizer

Jim Lux jimlux at earthlink.net
Tue Oct 7 13:02:55 EDT 2014

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, 

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 

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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