I stand corrected re: W2AU v W2DU.
Nevertheless, Walt's comments did apply to some manufactured products.
On 3/15/2017 8:04 PM, Jim Brown wrote:
Wes,
I think you may be confusing W2AU-branded parts with W2DU's. Walt's original
common mode choke design paper was excellent -- as I'm sure you know, he built
and tested units with 50, 100, and 200 #73 Fair-Rite beads. The 200 bead
design was the best, but the commercial products I know of use only 50 beads.
This makes them far less effective and also greatly reduces their power
handling. Walt's choice of #73 was excellent -- it causes the choke to have a
predominantly resistive impedance from 80 - 15M. That cheapie trick of the mfr
is what makes them a fuse -- the greater the resistive impedance, the more
power than can handle.
And, of course, some folks who failed to understand the need for resistive
impedance, not reactance, started telling people to use #43 cores. And after I
showed the virtue of the new (around 2003) #31 material, those who didn't
bother to read my tutorial showing how chokes work decided that a string of
#31 cores was even better. Which it is NOT, except on 2M. :)
73, Jim K9YC
On Wed,3/15/2017 7:40 PM, Wes Stewart wrote:
It's disturbing to me to see my late friend Walt Maxwell, W2DU, disparaged
this way.
Walt addressed this issue before his passing here:
http://www.eham.net/reviews/detail/2300
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