Re: Tuning Experiments

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Paul Nicholson by way of Terry Fritz <teslalist-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>

What a great series of experiments, and the results all make
perfect sense.

Steve Young wrote:
 > Wire length   F res kHz
 >  0            191.4
 >  6            190.3
 > 12            187.8
 > 18            185.2
 > 24            181.9
 > 30            179.0
 > 36            176.2

These detunings are very typical of primary detunings measured
after the coil is tuned for best performance.  See for example
the primary tuning offsets in

  http://www.abelian.demon.co.uk/tssp/cmod/

We get the impression that primary coils are tuned several percent
below the unloaded secondary Fres.  I would say your wire streamer
does a good impersonation of the reactance of a real streamer.

 > resistance      F res kHz
 >   0             182.3 deep dip
 >   1K            182.2 deep dip
 >   10K           182.2 shallow dip
 >   100K          no dip!
 >   220K          no dip!
 >   470K          189.0 barely perceptable dip
 >   1 meg         189.7 shallow dip
 >   10 meg        189.7 deep dip

Very nice.  In the region of 100k or so your applied RC load is
terminating the coil close to its output impedance, therefore
applying maximum damping to the coil resonance.  This is the
ideal load for max power transfer into the streamer.  Don't
worry about the fact that the resonance is being damped out
of existence - that's exactly what you want: energy from the
resonance going into the load.

We can calculate the series resistance which will give the
least dip (max power transfer to streamer) for a given coil,
topload, and streamer length.  I guess you want to go the other
way - calculate the size of topload for max power transfer to
a given streamer.  If we knew the specific resistance - ohms per
foot say, of a typical streamer we could do that.

 > I found that when measuring primary F res I had to either
 > remove the secondary ...

Yes, it's not possible to measure Fpri with the secondary
present.

 > I figured if I tuned the primary to the secondary resonance,
 > with a wire simulating the streamer, it would be fairly close.
 > I am not so sure now.

I think that should be a great way to tune the coil.  Why not tune
the coil in that manner and then test it with streamers.  Tune it
each way to see that the performance goes down when you depart from
the wire-streamer setting.
--
Paul Nicholson
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