On 5/4/2020 8:51 AM, Grant Saviers wrote:
Has anybody characterized these as alternatives to Fair-Rite #31?
A major problem with products from ferrite vendors other than Fair-Rite
is that their technical data sheets don't come close to providing
sufficient information to an engineer trying to use them for anything
other than a single pass through the core. I spent more than a year
measuring hundreds of samples (that I had to buy) of the two Fair-Rite
#31 cores that were useful, selecting cores at the limits of their
tolerances, winding and measuring chokes on each of those limits cores,
entering data in spreadsheets for each core, and producing winding
recommendations on the basis of worst case cores for each band.
#31 material is quite unique, in that it is an MnZn material whose
dimensional resonance and circuit resonance combine to provide high
bandwidth at HF. It is also rather lossy in that range, which is
important for chokes.
Most other materials are NiZn, and are far less lossy, which means
higher Q, which means a narrower resonance, which, combined with very
broad component tolerances, makes choke designs far less repeatable.
THIS is why Fair-Rite #43 and #52 are far less useful at HF.
Last year, seeing G3TXQ's recommendations for chokes on #52, I bought
ten cores each from four different industrial distributors that stocked
them and repeated the process of selecting limits cores, then winding
chokes based on his recommendations. I could not repeat his results, NOT
because of measurement error on his part (his setup was excellent), but
because of component tolerances.
Others are selling #77 or #78 cores as a solution for HF, but the
dimensional resonance of these MnZn is in the AM broadcast band, making
them far less useful at MF or HF. Simply put, they are power products
for use in low frequency electronics, not for suppression, and the
Fair-Rite catalog makes that clear.
73, Jim K9YC
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