Am 30.03.2016 um 21:20 schrieb Bruce Griffiths:
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. 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.
It doesn't take conical inductors to separate the baseband from the
carrier at 10 MHz. The
world existed before Piconics and their conical L patents. Yes, we used
them in our 10 GB/s
fiber optic transceivers, just to see what eye diagrams we could
achieve. But at €38 a pop they
never ever made it into production. It was just too easy to replace them
with somewhat more cent stuff.
A colleague even rolled his own from wire, epoxy glue and ferrite beads
smashed in a mortar.
That looked, hmm, ugly, but performed excellently. Now, you get them
from MCL and Coilcraft.
But for a 10 or 100 MHz lowpass, that's way over the top. Not even if
you are nuts.
regards, Gerhard
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