From: bill.sloman@ieee.org   
      
   On 14/11/2025 2:25 am, john larkin wrote:   
   > On Thu, 13 Nov 2025 15:44:26 +1100, Bill Sloman    
   > wrote:   
   >   
   >> On 13/11/2025 5:02 am, john larkin wrote:   
   >>> On Wed, 12 Nov 2025 17:28:04 GMT, Jan Panteltje    
   >>> wrote:   
   >>>   
   >>>>> john larkin wrote:   
   >>>>>> On Wed, 12 Nov 2025 16:11:03 +1100, Bill Sloman    
   >>>>> wrote:   
   >>   
   >>    
   >>   
   >>> The problem is to find an audio spectrum analyzer with -150 dB   
   >>> distortion.   
   >>   
   >> Not if you filter out almost all of the fundamental before you feed the   
   >> residual signal into the spectrum analyser.   
   >   
   > You just shifted the problem to finding a filter with -150 dB   
   > distortion.   
      
   So you wouldn't use ferrite-core inductors to make it, and you might   
   need two made with different components to check if they produced the   
   same result. Twin-T narrow-band filters can be pretty sharp, but you   
   would probably need to twiddle a pot to keep them at the right frequency.   
      
   --   
   Bill Sloman, Sydney   
      
   --- SoupGate-Win32 v1.05   
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