On 4/28/15 6:56 AM, Bob Good wrote:
Other than using the sales / technical literature, how can I measure
the resistance of ferritecore or beads to ensure that I have the
recommended 5000 ohms resistance?
If you have a R/X meter or VNA or antenna analyzer or similar.. you can
wind a few turns of wire through the core and measure the R and X vs
frequency.
Jim's RFI-Ham pdf has some examples.
#31 is very good for lots of HF applications. But it is not available
in as many physical form factors (I use 2.4" diameter toroidal cores for
everything, and they're definitely available in #31)
Every manufacturer has their own numbering/coding scheme, although a lot
of people use Fair-Rite's numbers (73, 31, etc.) are FairRite numbers.
Of course, there's no guarantee that a #50 core from Mfr A is going to
be the same as a #50 core from Mfr B. If you are faced with a box of
cores of unknown origin (e.g. no data sheet with them), then you're
really stuck unless you just measure them.
There are an enormous number of ferrite cores out there intended for RFI
management at VHF frequencies from the consumer electronics industry,
and they show up surplus all the time.
I gather that the resistance is
frequency dependent and rises as frequency increases. Also I gather
that the best overall mix for HF is #73. I assume this designation
is universally recognized regardless of the supplier? Can you help
shed some light for this Old old timer? Thanks, Regards, Bob K4BG
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