[time-nuts] fast switching quiet synthesizer

Don Latham djl at montana.com
Tue Oct 7 16:19:13 EDT 2014


I have two "versions" of the ADF4351 dds. One is the AD eval board, and the
other the TPI synthesizer
(http://www.rf-consultant.com/calibrated-signal-generator/) at $280 that might
do the job. The latter device performs well. It will be as good as the 4351, I
think. It has a programmable attenuator. A good price.  Requires a Healthy!
USB port.
Don


Magnus Danielson
> 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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-- 
"The power of accurate observation is commonly called cynicism by those who
have not got it."
 -George Bernard Shaw

Dr. Don Latham AJ7LL
Six Mile Systems LLC
17850 Six Mile Road
Huson, MT, 59846
mail:  POBox 404
Frenchtown MT 59834-0404
VOX 406-626-4304
Skype: buffler2
www.lightningforensics.com
www.sixmilesystems.com





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