From: bill.sloman@ieee.org   
      
   On 20/11/2025 2:35 am, john larkin wrote:   
   > On Sun, 16 Nov 2025 11:38:30 -0500, "Learning Math"   
   >  wrote:   
   >   
   >> "Liz Tuddenham"  wrote in message   
   news:1rlu0li.q2j8lgo7515oN%liz@poppyrecords.invalid.invalid...   
   >>> Bill Sloman  wrote:   
   >>>   
   >>>> On 15/11/2025 4:46 am, Liz Tuddenham wrote:   
   >>>   
   >>>   
   >>> [...]   
   >>>>>   
   >>>>> The Johnson noise of a 50-ohm resistor at 20 C with 5 Kc/s bandwidth is   
   >>>>> -130 dBm.  If we take the rail-to-rail output voltage of an op-amp to be   
   >>>>> about +20 dBm, that gives 150 dB difference.   Claims that a device is   
   >>>>> capable of achieving this sort of figure in any practical situation is   
   >>>>> stretching the limits of credibility.   
   >>>>>   
   >>>>> If the signal is lower than +20 dBm, you either have to start cooling   
   >>>>> the device or reducing the measurement bandwidth, otherwise 150 dB S/N   
   >>>>> ratio is impossible to achieve.   
   >>>>   
   >>>> Johnson noise is broadband. The harmonic of interest in evaluating a low   
   >>>> distortion sine wave oscillator are rather narrow band.   
   >>>   
   >>> When you get down to signals as low as -150 dBm there will be Johnson   
   >>> noise and intermodulation products contributed by the components within   
   >>> the oscillator.  Selecting individual harmonics with a narrow-band   
   >>> filter will give an unrealistic number that doesn't represent the total   
   >>> unwanted output.   
   >>>   
   >>>> You are comparing apples and pears as your "5 Kc.s bandwidth" makes   
   >>>> clear. if you have been cribbing from a more modern source it would have   
   >>>> been a 5kHz bandwidth.   
   >>>   
   >>> You have no idea what I did, so stop posting offensive nonsense.   
   >>   
   >> That's not going to happen so I will be ignoring Sloman as of now.   
   >   
   > He rarely says anything interesting on-topic (on any topic, actually)   
   > and inevitably steers any thread towards insults.   
   >   
   > As his followup will surely do.   
      
   John Larkin experiences any response that fall short of fulsome flattery   
   as an insult. He doesn't post much that is worth saying anything nice   
   about, and posts a lot that earns critical comment (and he really   
   doesn't like that).   
      
   --   
   Bill Sloman, Sydney   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)