Re: 7.1Hz, how the heck did Tesla succeed?

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: William Beaty <billb@xxxxxxxxxx>

On Sat, 16 Jul 2005, Tesla list wrote:

> >What goes wrong is that the received signal is way down in the noise,
> >therefore exotic antenna techniques become useful.
>
> If the signal is in the noise no exotic antenna will help you.

If the noise is mostly thermal noise from the wire, then it would help if
we can somehow crank up the amount of EM energy being received.  I think
this was the whole point of their paper.   I'll have to look it up.


> >Another problem is that the bandwidth of a detector varies in inverse
> >proportion to sampling time, so a narrowband signal which wanders randomly
> >will be wrongly interpreted as a wideband signal .  Regardless of whether
> >the detection is performed live, or via sofware w/files, if (say) you
> >sample at 1Hz but only for 0.1 second, the instrument will have chopped
> >the signal and therefore falsely receives it as a wide band signal.
>
>
> But, that's not that was suggested.  what was suggested was sampling @
> 100 %  for a very Long time.


I think you don't understand.  Do you propose to measure the shape of a
signal's spectral line ...without using any narrowband filters?  The
measured spectrum of any signal is convolved with the shape of the
sampling filter, so if you don't use a narrow filter, a very narrow signal
spectrum will look like your wide filter.  But if you *do* use a narrow
filter and long sampling times, then if the frequency of that narrowband
signal wanders around, it will be measured as having a wide spectrum.
But we don't know if that signal is actually wandering around in
frequency, or actually has a wide spectrum, since it's buried in noise.
And in order to extract it from noise, we have to sample for a long time
using narrow filters.  But this method of extracting it from noise is bad
if the signal is moving around: it gives out an entirely wrong spectrum.

Get it?  We can't SEE the signal except through "lenses" of long sampling
times which distort a certain type of signal.   Making long measurements
in order to pull a signal up from noise...  this technique can't tell the
difference between a signal with a wide spectrum and a narrow signal that
moves in frequency.   So the true value for Earth cavity Q is possibly
unknown.

But this is all somewhat beside the point, since the Sutton/Spaniol paper
said that these measurements were all done decades ago with lousy
equipment using sampling filters with too wide a band.  The calculated Q
is caused by the wide filters on the equipment, and the true Q of the
Earth cavity MIGHT be very different...  yet everyone has been relying on
the wrong published data ever since those old measurements.


> >To
> >make narrowband measurements you have to make longterm measurements.  If
> >the signal frequency is changing, then you can't measure it with
> >narrowband filters unless you know just how it's changing.
>
> Sure you Can. Simple example is a phase locked loop tracking a sine wave
> that's slowly varying.

BUT THESE SIGNALS ARE BURIED DEEP IN NOISE!  Jeeze.  What is going ON
here?!!!  A PLL doesn't work.  If we could see the darn things on a scope
or measure them with a frequency counter or lock them to a PLL, then we'd
instantly know if the frequency was stable or varying.  But if all we have
is extremely noisy data, then spectrum analysers need long integration
time, and this prevents us from knowing if a particular signal's spectral
line is as wide as measured, or perhaps the line is actually narrow, but
is wandering during the (necessary) long measurement.

If the line is narrow, then the Earth cavity Q is high.



>
> >  That's why
> >spread spectrum comm is used: the frequency hopping is a *huge* problem
> >unless you know the code.
> >
> > > and exact Fo frequency "jumping around" is not problem at all...
> >
> >Totally wrong because the jumping around, combined with the narrowband
> >filters, will chop the signal and add a wideband artifact.  Or do you have
> >an explanation for how a spread spectrum signal which is deep down in the
> >noise can be easily received when you don't know the random sequence of
> >frequencies?  If frequency jumps caused no problems, then spread spectrum
> >transmissions would give no security at all.  It's the same physics.
>
> Let's be careful here. There's two distinct problems you've described. The
> first is just detecting a spread spectrum signal.

In this "cell phone" analogy, just detecting the presence of a wideband
noiselike spread-spectrum signal is totally beside the point, it's
useless, it has no bearing on the problem.  I thought this was obvious.

What we want is this:

   Observe the true shape of a spectral peak


The problem is this:

   The peak is buried deep in noise


The solution is this:

  Use a spectrum analyzer (or software.)  Sample with many narrow
  frequency channels, and integrate over a long sample time in order to
  build up a high S/N ratio.


The solution fails because:

  If the spectral peak wanders around during the long sample time,
  and it successively moves from one narrow filter channel to the
  next and back again without us knowing it, then our software will
  display it as a wide spectral line; a line that doesn't wander around.
  The software lies.  But we must rely on the software if we want to
  see the signal through the noise.


Next solution?

  Don't rely on natural lightning signals, instead drive the Earth cavity
  with a huge CW signal that's easily detected far above the noise level,
  then turn off the transmitter and measure the ringdown waveform.

As far as I know, nobody except perhaps Tesla has ever done this down
at the frequencies we're talking about (below 1KHz or even 100Hz.)



(((((((((((((((((( ( (  (   (    (O)    )   )  ) ) )))))))))))))))))))
William J. Beaty                            SCIENCE HOBBYIST website
billb at amasci com                         http://amasci.com
EE/programmer/sci-exhibits   amateur science, hobby projects, sci fair
Seattle, WA  206-789-0775    unusual phenomena, tesla coils, weird sci