[Boatanchors] Xmtr impedance

[Ron]

--- fkamp at comcast.net wrote:

> StephenTetorka at cs.com wrote:
> > I like Ron's idea about using the non-inductive
> resistances.
> > 
> > Simple and data-worthy.
> > 
> > I have an old CQ or QST from the 30's having an
> article on making a 
> > non-inductive dummy load using resistance
> wire...I just happen to have a spool of 
> > nichrome at 0.406 ohms per foot.
> > 
> > Worth the try guys?
> > 
> > Any advice?
> > 
> 
> Lately I have become a little more careful about 
> giving advice.  Sometimes it does more to confuse 
> than help.  Other times, what I consider good 
> advice is not entirely without flaws.
> 
> A non-inductive dummy load using resistance WIRE!?
> 
> I was under the impression that all wire had a 
> certain amount of inductance.  Isnt that why we 
> use it build coils?  Isnt that why power resistors 
> using resistance wire are not suitable for 
> building non-inductive dummy loads?  Or is there 
> some construction method that eliminates the 
> inductance?  If so, does it work over a range of 
> frequencies?  How large a range?
> 
> If it were me, I would check to make sure the 
> article did not come out of an April edition.
> 
> Regards,
> Frank Kamp
> K5DKZ

Wire does have inductance, though it's rather
low. You can wind a non-inductive resistor by
wrapping the wire one way and for the next
layer, reversing direction and winding it the
other way. This way, each layer cancels the 
field of the layer under it. Just before the
final layer, measure inductance and see which
way you have to wind the next few turns to 
null (or minimize) it.

-- Ron


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