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" <[email protected]>
À : [email protected]
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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