Re: Measured Q (was Homemade chokes)

[Terry Fritz <twftesla-at-uswest-dot-net>]

Hi Ralph,

At 10:53 PM 8/12/00 -0400, you wrote:
>In a message dated 8/12/00 8:43:13 PM Central Daylight Time, tesla-at-pupman-dot-com 
>writes:
>
><< However, you really need a metal
> ground plan and some other "ideal" things to have the equations work out
> really close.  The Q is pretty sensitive to what (or who ;-)) is near the
> coil.  I can usually get to within +-50%...
> 
> Cheers,
> 
>    Terry >>
>Hi Terry,
>I know what a ground plane is in electrostatics but would you please explain 
>how
>a ground plane is used when making measurements on a TC?
>Also, what are these other "ideal" goodies?
>
>Cheers,
>Ralph Zekelman 
>

The secondary should be set on a counter poise or conducting sheet of metal
with radial slits in it (to stop eddy currents).  Otherwise the concrete
floor or table top can cause a significant variation from experiment to
experiment ;-)

Also the coil should be in free space which reads as a large room without
anything close to the coil to mess with the fields.

Then you have to drive it from a low impedance source and measure it with a
super high impedance probe.

Of course, all the dimensions and terminations have to be known very
accurately as well as the number of windings an all that.

Malcolm has done a lot in this area and he probably knows of more.  But
those are the things that can mess up Q measurements of secondary coils
that I can recall...

Cheers,

	Terry