Re: Variation of secondary Q

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

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Boris,

On 16 Mar 2002, at 6:19, Tesla list wrote:

> Original poster: "boris petkovic by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <petkovic7-at-yahoo-dot-com>
> 
> 
> Hi Malcolm,
> > >
> > >I have not heard back from Paul on this yet but
> > here are some other ideas.
> > >
> > >I could directly connect my 2.5pF 10Meg ohm probe
> > (Tek5100) directly to the 
> > >top of the coil for a read out like this:
> > >
> > >http://hot-streamer-dot-com/temp/PaulsQexp-3.gif
> > >
> > >The scope could then save a data file like this:
> > >
> > >http://hot-streamer-dot-com/temp/TEK00000.CSV
> > >
> > >The resonant frequency drops from 84.42 kHz to
> > 82.15kHz so the probe loading 
> > >is very low (Those are darn good probes!!  Like
> > Pearson stuff, they too are 
> > >made out of pure money :-))).  I imagine one could
> > back calculate the small 
> > >probe loading right out.
> > >
> > >However, assuming  Vtop = Q x Vin  we can just
> > input 1 volts RMS and read 
> > >out the top voltage for a direct Q reading along
> > with time and frequency and 
> > >just have all our data there without needing to do
> > anything but push the 
> > >save button ;-))  (may have to check for frequency
> > variation)
> > >
> > >http://hot-streamer-dot-com/temp/PaulsQexp-4.gif
> > >
> > >That almost seems too easy :o)
> > >
> > >If this is OK with Paul, it would be very easy to
> > do.  The scope can filter 
> > >it down and over sample like 512 times to get very
> > high accuracy.  But that 
> > >is probably over kill.  I am not sure this would be
> > 100% OK with Paul's 
> > >paper and all, but it should be close enough I
> > would think.
> > >
> > >I wonder if the Q variation is not so much the coil
> > changing but the 
> > >surroundings changing with weather?  The coil is
> > far more stable for 
> > >temperature and humidity than the ground, walls,
> > ceiling, etc.  Just a 
> > >thought there.
> > >
> > >Cheers,
> > >
> > >	Terry
> > >
> > >
> > snip...
> 
> Hi Malcolm ,Terry,
> 
> The fact is that Qs can change as type of ground plane
> soil and other settups  change.
> Latest trades  also suggest that phenomena of eddy
> current losses in nearest primary turns carry away
> some energy.
> Thus ,the change of secondary Q should be noticable in
> msm with or without primary coil in place.
> This especially holds true for very high Q
> secondaries.
> 
> Regards,
> Boris

With the test whose results I reported, test were performed in a 
large room with a minimum clearance of 6' on all sides and the coil 
elevated so that it was sitting more-or-less centrally between 
concrete floor and ceiling. The probe was positioned about 6' from 
the top of the coil with the connecting lead running radially away. 
No primary was present. The coil was base fed by direct connection 
from a signal generator with the connecting lead running vertically 
to the floor then radially away from the coil.

Regards,
malcolm