[time-nuts] Ebay FE-5680A Rb: Are they that good?

Javier Herrero jherrero at hvsistemas.es
Fri Dec 9 08:32:55 EST 2011


Yes, I know that the phase noise is the spectrum analyzer one, but the 
spurious that are around (mostly -70, -80dBc) are not, particularly the 
ones at +/200kHz and +/-400kHz. I was mostly curious about the harmonics 
and other spurii since in this unit, 10MHz are generated from a CPLD 
divider, and this approach sometimes leds to strange spurious and nasty 
things around, but in this case seems not bad. As far as I remember, in 
a FRS-C the output is from a 10MHz crystal oscillator.

And the harmonics, well... usually we square that output and they have 
not importance, but sometimes it is desirable to have a clean as 
possible signal, and I was curious to see how good (or bad) the 
filtering was :). On other side, we can use square wave from the CPLD 
(not yet checked, but it must be there inside, somewhere :) ). The 2nd 
harmonic is very low, that indicates that square wave symmetry is very good.


Javier, EA1CRB

El 09/12/2011 14:10, Marco IK1ODO -2 escribió:
> Javier,
> the plots are nice, and I did the same years ago for an Efratom FRS-C. 
> Found about the same data. The only point is that with the spectrum 
> analyzer you see the S/A pahse noise, not the Rb, wich has to be 
> orders of magnitude lower.
> About the comments on the waveform and harmonics contents: who cares 
> about having the 2nd harmonic at -30 or -50 dB? For any practical use 
> one has to square the signal, and the original harmonic content is of 
> no pratical interest, or I am missing something ...
> 73 - Marco IK1ODO / AI4YF
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