TSSP: List Archives

From: boris petkovic
Date: Fri, 8 Sep 2000 03:52:32 -0700 (PDT)
Subject: Re: [TSSP] Mystery of the missing loss



> With a pristine foil ground plane:
> 
> Bare Coil        Coil at 1"   Coil at 12.5"
> f1 = 148.3kHz     Q = 57.7      Q = 61.7
> f3 = 347.87kHz    Q = 33.3
> f5 = 513.76kHz    Q = 20.3
> 
> 45 inch Torroid
> f1 = 97.93kHz     Q = 80.9      Q = 97.3
> f3 = 322kHz       Q = 36.6
> f5 = 491.2kHz     Q = 23.8
> 
> Thanks again Terry. These figures, together with
> your measurement
> on the effect of a shorted loop around the coil,
> give me a total
> of 9 numbers with which a model must simultaneously
> agree with.
> 
> Some comments,
> 
> Terrell W. Fritz wrote:
> 
> > So moving the coil further away from the eddy
> currents, or
> > whatever, of the plane did not have a "dramatic"
> effect on Q...
> 
> Perhaps not dramatic, but significant I think - a
> 20% improvement.
> 
> > The coil's Q seems to vary much depending on hard
> to control
> > (at least in one's basment) factors.  Perhaps if
> some "standard"
> > evironment or setup could be extablished that
> would go well with
> > the math models, we could take Q reading more
> consistently.
> 
> I disagree. I think your basement setup is rather
> good - it's
> reasonably stable and well defined. OK, the
> individual readings
> are bound to wobble a bit, but a clear pattern does
> emerge. 
> 
> > I fear the best expermenters trying to reproduce
> the same Q
> > measurements could get fairly large errors
> depending on a number
> > of little factors.  I would guess that +-20%
> accuracy is all
> > that could be expected.
> 
> I'll be a little bit more optimistic and go for +/-
> 5%. Let me
> throw in a quick input impedance comparison with
> Mark's small,
> elevated coil, which I'm still working on,
> 
>     Zin meas    Re(Zin) model
> f1   64.0 ohms     67.9 ohms
> f3  118.1 ohms    119.5 ohms
> f5  162.3 ohms    168.7 ohms
> 
> Terry, thanks to your efforts we've got a pretty
> good set of
> measurements against which to test models of eddy
> current losses
> in the ground plane. I've now got all the formulae
> gathered
> together and can set about incorporating an eddy
> current loss
> estimate into the program. That'll keep me busy for
> a week or
> so, meanwhile I'll refrain from suggesting any more
> experiments!
> 
> Bryan Steinbach wrote:
> 
> > Perhaps a better choice for a gnd might be sheet
> metal on a
> > hard floor.
> 
> That may be a good way to go in some situations.
> Accept the
> large eddy currents but make sure they circulate in
> a high Q
> ground plane. The advantage - the circulating
> currents will
> raise their own B field which will tend to cancel
> the coils'
> B field which would otherwise extend further into
> the ground
> and perhaps encounter a higher loss material - this
> is the
> 'screening can' approach.
> 
> Regards All,

Hi All,
Althought,I have been present on TSSP list from its
first days,this is first post of mine (very occupied
lately,and can't manage to check email on regular
basis as I used before:))

Few comments regarding measured too low Q :
Whenever I see measured Q of unloaded secondary  
  in order of 50 I can claim:
If Z coil is resonably high ,which in most TC
secondaries is,low Q could be the result  of following
things:
1.)Rdc is too high becouse of too thin wire diameter
used.
 2.)Something is poorly made in secondary construction
such as shorted turn top isotropic capacity effect
apperance,nonlinear wounding and eddy currents loss
area presence etc.
3.)Possibly extra high dielectric loss in coil form 
 (unlikely here I think)
4.)EM Coupling of secondary with enviroment and losses
outside a coil structure.

I don't belive that Terry made serious mistakes
relating 2 and 3.Neither that the reason for very high
Garry Johnson's secondary coil Q in order of 500  
is some kind of superior secondary construction.
But I do belive it is due to point 4.
That would be the reason:Enviroment and resonator
position in it.
I'm quite convinced Terry's secondary coil Q results
would be much better in different enviroment
conditions.
   
Regards,
Boris

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