On Mon,11/30/2015 3:11 PM, Jim Lux wrote:
On 11/30/15 9:17 AM, Jamie Tolbert wrote:
What tpe beads do I need, 43 or 73? length? 4 ft, 100 beads seems
awfully long.....
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I use 31 mix for this kind of choke application.
#73 is the ONLY material suitable for use in a "string of beads" choke
because it is the only material with a single turn impedance that is
predominantly resistive at HF. Unfortunately, the largest #73 beads just
barely fit RG58 and other specialty miniature coaxes.
what is your operating frequency?
http://audiosystemsgroup.com/NCDXACoaxChokesPPT.pdf
see pages 22-25
73 is better in general, 43 is ok for low frequencies
31 isn't great for bead baluns..
#43 and #31 are NOT acceptable for "string of beads" HF chokes (that is,
a lot of cores on the coax line), because they are inductive at HF. To
be effective, the choke must be strongly resistive at the operating
frequency. A single turn through these core materials resonates around
150 MHz, far too high to be useful at HF. We can use #31 and #43
material by winding multiple turns through the core(s) to lower the
resonance to the part of the HF spectrum where we want to use the choke.
Luckily, it's a very low Q resonance (typically around 0.5), so the
resonance is quite broad. This allows a choke to cover 3-4 adjacent bands.
My best tutorial on this is k9yc.com/RFI-Ham.pdf It's worth studying.
I did the work to learn (and support it) beginning around 2003 and
continuing to around 2010. It is, I believe, the basis of all modern
thinking about how common mode ferrite chokes work.
73, Jim K9YC
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