This snide remark ignores the fact that it is generally not practical (nor
is it good politics) to go inside your neighbor's equipment to add bypass
capacitors. Nor is it practical to open up a wall wart, nor even most
consumer equipment. It also ignores the fact that much of RFI at HF is
common mode, not differential mode, caused by bonding failures (the Pin
One Problem and its power systems equivalent). And it ignores the fact
that it is often the cable shield or the power system equipment ground
that is carrying the RF noise current, for reasons noted in my earlier
post.
It isn't a snide remark, it is how we focus on chokes.
Any filtering or decoupling system works by the ratio of series impedance to
shunt impedances.
A series choke is useless unless there is some value of shunt impedance in
the system. As a matter of fact, lack of established shunt impedances is
what can drive choke requirements to unrealistic values. This is true in
baluns, just like it is in line filters.
Most outlet strips and devices have room inside for several UL/CSA/ VDE
approved bypass capacitors. Rather than paying $30 or much more for some
capacitors in a physically large filter can, with minimal choke impedance
inside, one might consider a few well-spent dollars for external components.
Many times RFI is cured simply by bypassing and closing a loop through a
device, where choke requirements alone would be astronomical or ineffective.
73 Tom
_________________
Topband Reflector Archives - http://www.contesting.com/_topband
|