[time-nuts] OXCO Spurious Output at Line Frequencies

[Stéphane Rey]

Hi Martyn,

For such measurement you may shield your DUT and instruments. Ever using 
a shielded room which might not be easy for everyone or using shielded 
tents. You can find them made custom for 600-1000€ depending on the 
size. I've just ordered two of them from a company in netherlands

For main line frequencies, you may differentiate what is conducted from 
what is radiated. For EMI, I'm using now active low pass filter at very 
low frequency to follow my low noise regulators and I get very good 
result, but honestly not tested as low as -130dBc... But on low noise 
PLL or oscillators I can get rid of any spurious from PSU but at 50Hz, 
my noise floor has never reached -130dBc...  I'm working on a very low 
noise generator (20fs jitter 10Hz-1Mhz) at the moment and at 50 Hz, the 
phase noise is  -80dBc/Hz which is already not bat at 6 GHz

I've measured last week a Wentzel VCXO giving -150dBc/Hz @ 50 Hz and I 
could measure the 50 Hz at -130dBc/Hz but this had not the active filter 
on it. I test it again using the shielded tent exactly to know what is 
radiated from conducted. If still there under the tent I will try using 
my active filter to see if this makes a difference.


Cheers
Stephane

------ Message d'origine ------
De : "Martyn Smith" <martyn at ptsyst.com>
À : time-nuts at febo.com
Envoyé 12/07/2016 12:44:31
Objet : [time-nuts] OXCO Spurious Output at Line Frequencies

>Hello,
>
>I have a customer who is measuring the phase noise of my 10 MHz 
>ultra-low phase noise frequency standard.
>
>He is seeing spurious signals at line frequencies (50 and 100 Hz as we 
>are in Europe) at a level around -130 dBc.
>
>My opinion is that it's impossible to get much better than that.  Even 
>running on batteries make little difference, since the equipment is in 
>a test rack with AC signals everywhere.
>
>Even the £50k R&S test set he is using only quotes a spurious spec of 
>-90 dBc.
>
>What experience does anyone have here?
>
>Best Regards
>
>Martyn
>
>
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