[time-nuts] fast switching quiet synthesizer

SAIDJACK at aol.com SAIDJACK at aol.com
Tue Oct 7 17:18:19 EDT 2014


Hi Anders,
 
in the absence of a true phase noise analyzer the next best thing is to use 
 one of the Agilent 856x analyzers with the phase noise measurement 
software  plug-in.
 
By chance I had looked at Ebay over the weekend and those two can be  had 
for around $3500 these days (with an 8561E). Still a lot of $$, but it will  
give you a nice improvement over the Rigol spectrum analyzer and still be  
5x cheaper than the lowest cost commercial PN analyzer.. Its really cool to 
have  a good SA of course, so the PN option just comes as a bonus in my 
opinion.
 
Attached is a sample plot of what that PN output would look like at 100MHz  
from a reasonable DDS output. The noise floor is about -135dBc/Hz.
 
bye,
Said
 
 
In a message dated 10/7/2014 13:44:31 Pacific Daylight Time,  
anders.e.e.wallin at gmail.com writes:

The  spurs improve when using the DDS with an external 1GHz  sample-clock
(internal PLL+VCO on the DDS-chip disabled). We produced it  from 10MHz with
an ADF4350  eval-board:
http://www.anderswallin.net/wp-content/uploads/2014/03/100MHz_AD9912_interna
l_vs_external_PLL.jpg
AD  must use some nice&expensive spectrum-analyzer to produce that  figure
with a -100 dBm noise floor!  :)

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