Hi Jeff does not suprise me.
Read the link in Jims email single beads do not cut it.
~73
Don
KD8NNU
FH#4107
-.- -.. ---.. –. –. ..-
On Sat, Feb 14, 2015 at 1:56 PM, Jeff Hall wrote:
Thanks Jim, I'll give it a read and order up some mix-31 toroids.
Does it surprise you the KAT500 is getting power cycled as I
described? Is it really that sensitive? 10 of the ferrite beads I got
from DXStore (rated for 150MHz or lower) work fine for 10m-20m. But no
dice on 40m, so I guess the frequency is just too low for them to be
effective (or perhaps I'd need like 50 of the suckers!)
-Jeff
On Saturday, February 14, 2015 10:06 AM, Jim Brown
<j...@audiosystemsgroup.com> wrote:
On Sat,2/14/2015 9:48 AM, Jeff Hall, W6UX wrote:
can anyone suggest some further experiments to try?
Yes. The problem is that ferrite beads slipped onto a transmission
line does NOT make an effective common mode choke. Those beads are
inductive, and, depending on the length of the line and the operating
frequency, many lines look capacitive. The inductance resonates with
the capacitance, and the common mode current increases.
To be effective as a common mode choke, we need a high value of common
mode impedance, and the best way to get there is with a high value of
RESISTANCE. We obtain that by forming a low-Q parallel resonant
circuit -- we wind multiple turns of the feedline through a lossy
ferrite toroid or clamp-on. The number of turns needed depends on the
ferrite material and the operating frequency. The best ferrite
material for the HF bands is Fair-Rite #31, because it has the lowest
effective Q over the widest frequency range.
Study k9yc.com/RFI-Ham.pdf and use the Cookbook as a guide to wind
the chokes you need. The chokes are most effective at the feedpoint of
your antennas.
73, Jim K9YC
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