[time-nuts] fast switching quiet synthesizer

Jim Lux jimlux at earthlink.net
Tue Oct 7 19:44:02 EDT 2014

On 10/7/14, 12:43 PM, Anders Wallin wrote:
> We've been using/testing an AD9912 eval-kit board. It can take 10MHz input
> and has an internal 66x PLL and VCO for a 660MHz DDS sample-clock (just out
> of spec actually, vco is min 700MHz if I read the datasheet correctly).
> Output looks like so:
> http://www.anderswallin.net/wp-content/uploads/2013/12/Fout100M_Span400M.bmp
> DDS output is 0 to 2-400MHz with a resolution of ~few uHz since it has a
> 48-bit tuning word. We're programming it with an arduino+eth-shield using
> modbus-ethernet. Changing frequency over ethernet takes about 60ms, but it
> could be much much faster directly over SPI if you know the desired
> frequencies beforehand and store them on the arduino.

That's what we do now.. We actually use Teensy 3.1s, but same idea.. 
Store the table in the Teensy and use it to clock it out. And it's 
pretty easy to synchronize multiple Arduinos/Teensys to the "sub 
microsecond" level using interrupts

But then there's the building boards and cables and putting it in a box. 
  If I have to build 3 or 4 of these (or a half dozen) it's 
realistically a couple weeks work (which I'm paying a substantial sum 
for) by the time you find the box and connectors in the catalog, order 
it from Digikey/Mouser/Allied/Newark, get the holes drilled in it, mount 
the boards, etc.

If I can just BUY something off the shelf that does it, that would be 

For instance, MiniCircuits (and others) have what are essentially a 
PLL-VCO in a box running off USB.  But they
a) don't have real fast settling time
b) aren't easy to synchronize

That's why I was thinking PTS or something else.

> even with the eval-boards there's a fair bit of building: multiple
> powersupplies, cables, enclosure, etc.

And those AD parts run HOT, and they're temperature sensitive.  I 
remember all sorts of hassles with the AD9854 on the early Flex-Radio 
units (a fan blowing on the part helps).

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