[time-nuts] Oleg' s PN test Re: A new member & PN test set
Bruce Griffiths
bruce.griffiths at xtra.co.nz
Wed Mar 30 18:32:40 EDT 2016
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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