On Thursday, March 31, 2016 08:20:19 AM Bruce Griffiths wrote:
> The first inductor self resonance is much lower than it need be. EPCOS have
> a range of inductors which have a much higher first self resonance
> frequency.
> 
> The other problem is that inductors have several resonances alternating
> between parallel and series resonance. In short, your inductor model is
> inadequate and gives false predictions. You actually need to measure the
> filter response.
> 
> Conical inductors are available that are effectively resonance free to 40GHz
> but the largest value is around 10uH. In principle one could wind one's own
> conical inductor with a larger value, However an iron powder (carbonyl iron
> - available from Ukraine at least via ebay) and epoxy mixture

 filling/core is required. 

>  A cone angle of about 15 degrees appears to be suitable.
> 
> Failing that, the classical method is to use a series string of inductors of
> increasing value. Even then the various resonances need to be damped. Lossy
> Ferrites and resistors can be useful, however one has to be careful not to
> increase the noise at frequencies of interest.
> 
> Bruce
> 
Note correction above.

Bruce


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