On 8/4/2025 7:44 AM, Brian Beezley wrote:
Q is not easy to accurately measure for big coils like those sold by
QCoil. The fields may extend quite a distance and interact with nearby
objects, such as the instrument enclosure or even your body.
I am continually amazed with the placement of air-wound pi net inductors
just an inch or less from the side walls of final amp compartments, and
in other examples such as antenna tuners. Even Ameritron amplifiers
occasionally show such mounting. My Elmer taught me long ago that to
minimize the effect of such surfaces upon tuned circuits, always keep
the inductor at least a coil-diameter away from a solid surface. That
advice has stood me in good stead through the years. When I've had
access to reliable Q-meters, experiments with large coils and solid
nearby surfaces has always shown some detrimental effect upon the coil's
Q by the surface.
Steve, K0XP
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