[time-nuts] Unified VCXO Carrier Board

Gerhard Hoffmann dk4xp at arcor.de
Tue Oct 27 13:03:27 EDT 2015


Am 27.10.2015 um 13:50 schrieb Charles Steinmetz:
> Gerhard wrote:
>
>> Since the LM329 was mentioned above, I tried it also. Another surprise.
>> HOW CAN THEY MAKE SUCH A NOISY SUBSURFACE ZENER???
>>
>> 0 dB = 1nV/sqrt Hz
>
> The datasheet for both NS and LT LM329s shows broadband noise of 
> <70nV/sqrtHz, with a corner at ~100Hz, rising to a touch over 
> 100nV/sqrtHz at 10Hz.  That is consistent with the LM329s I have used. 
> So, according to the datasheet, the 10Hz noise ought to be a touch 
> above 40dB on your graph and the curve should level off above 100Hz at 
> about 30dB -- if I have done my dBs right. Still somewhat higher than 
> most of the other diodes you tested, but not outlandishly so.
>
> Your data seems to be *much* worse than this, with a 1/f noise corner 
> at ~10kHz (!!), rising to what appears to be about 1mV/sqrtHz (!!) at 
> 10Hz.  Is it possible you got fakes?  (I know someone who 

It's bad, but not that bad.  10 times the voltage is 20 dB more. So

0dB   = 1nV/sqrt Hz
20 dB = 10 nV
40 dB = 100 nV
60 dB = 1uV
80 dB = 10 uV/sqrt Hz

The wideband noise at, say, 46 dB would be 200 nV/sqrt Hz  versus the 
claimed 75 nV typical
but the corner frequency is really bad. I bought them last year from 
Digi-key, still with
National as manufacturer on the bag, not TI.

I'll test a few more next weekend.

regards, Gerhard



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