[time-nuts] Ebay FE-5680A Rb: Are they that good?
bell.peter at gmail.com
Fri Dec 9 08:43:22 EST 2011
Getting the square wave out is easy - if you follow down the trace
from that J8 socket (which is also connected to the output on the
D-type) it goes to a cap - just remove that and solder a jumper across
the pair of pads to the left of it (I.E. closer to the PLD).
On Fri, Dec 9, 2011 at 9:32 PM, Javier Herrero <jherrero at hvsistemas.es> wrote:
> 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:
>> 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
>> 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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