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Re: New formula for secondary resonant frequency
Original poster: "Kurt Schraner by way of Terry Fritz <twftesla-at-uswest-dot-net>" <k.schraner-at-datacomm.ch>
Hi Paul, all
- Well, here is
the update of my coil-measurement data, after doing little
effort, regarding the "bottomless pit" of precision, and
eliminating gross errors. The warm weather here, in continental
Europe, allowed to perform some outdoor tests. But I was not able
to move the B&W secondary there out, 'cause I'm not able to move
the 48kg alone (.... I'm almost 62!). So I've replaced B&W by
a newbie-baby-candlestick small 2"x16" low-performance coil,
which was at hand. New data for B&W will be supplied later. In
order to preserve reference to the former postings, I keep the
order of data ~as before, but add new items, were appropriate.
------------------------------------------------------------
Outdoor measurements with distance to groundplane ~ 0.5m
Coil Sk-5cm Sk-12cm Sk-20cm Sk-Long
turns 934 894 943 1976
L -at- 1 kHz 5.203 mH 18.2 mH 46.33 mH 67.7 mH
Q -at- 1 kHz 1.52 8.95
DC resist.R 21.7 Ohm 21.0 Ohm 32.4 Ohm 55.2 Ohm
h 0.411 m 0.585 m 0.668 m 1.402 m
d 0.0511m 0.1212m 0.2052 m 0.161 m
b 0.503 m 0.49 m 0.49 m 0.545 m
awg 26.108 22.607 22.053 22.053
wd(insulated) 0.425mm 0.63mm 0.64mm 0.64mm
Fres,cal f1: 1068.4 411.8 208.9 158.0 Paul's
Diff 16.8% 1.6% -3.8% -2.1% cal-exp
Fres,cal f1: 923.8 380.1 199.4 139.3 Wh./Medh.
Diff 1.0% -6.2% -8.2% -13.7% cal-exp
Fres,exp f1: 914.76 405.1 217.22 161.45 kHz
Higher f3: ~947 497.8 386.43 kHz
f5: ? 709.9 562.04 kHz
f7: ? ? 710.32 kHz
f9: ? ? ~ 847 kHz
------------------------------------------------------------
Outdoor measurements with closer distance to groundplane
----- all values, except b, as above -----
Coil Sk-5cm Sk-12cm Sk-20cm Sk-Long
b 0.185 m 0.17 m 0.17 m 0.225 m
Fres,cal f1: 1057.9 407.5 206.8 156.7 Paul's
Diff 15.1% 1.2% -4.0% -2.1% cal-exp
Fres,cal f1: 923.8 381.6 199.4 139.3 Wh./Medh.
Diff 0.5% -5.3% -7.4% -13.0% cal-exp
Fres,exp f1: 919.45 402.8 215.43 160.05 kHz
Higher f3: ~ 945.4 496.07 385.09 kHz
f5: ? 709.3 560.30 kHz
f7: ? ? 710.08 kHz
f9: ? ? ~ 847 kHz
-----------------------------------------------------------
Instruments:
Siemens Level Oscillator W2087 (200Hz...1620kHz)
(buildt-in f-counter with XXXX.XX kHz display)
HP 180A Dual Channel Oscilloscope (50MHz)
Escort ELC-131D LCR Meter (for L+Q -at- 1kHz)
Metex M-3860M Digital Multimeter (for R with DC)
------------------------------------------------------------
Regarding harmonics: the small coils showed only none to very
weak signal, so I wasn't able to determine more. The Sk-20cm
coil is not the original one, but one of my 'spare part' coils
for the 2 twin coils, from which the former data were taken (yet
without corona ring). For all the coils I did new measurements of
the geometric data and turn counts. The turns are now based on
not less than 100 turns counted per coil, and extrapolated to the
winding length, which leads to about (+/-)5 turns precision for
the total (--> better to have a counter, when winding!). - The
outer wall of the house, was 1.9m away from the place, were the
coils were positioned for measuring. The ground floor surface was
humid but not wet, consisting of cobbles (in german:
"Kopfsteinpflaster").
I've noticed a problem in reliably measuring the resonant
frequencies of the coils: I've experienced an interaction of my
"signal generator - feed line - coil" resonance system, in the
way, that more capacity between generator and coil changes the
Fres to lower values (I'm using the practice, Malcolm Watts had
proposed in his "Electronics and Wireless World", March 95
article, downloadable from Terry's site*). It's probably an
impedance relation problem: signal-generator/transmission
line/coil. My high precision Siemens generator allows the choice
of output impedances between 600,150,...124 Ohm and ~ 0 Ohm
(marked as such!), and I choose the ~0 Ohm, and the highest
output level of +10dBm. I tried to narrow down the influence of
the transmission line by inserting a low ohm resistor at the
coil-end (10...50 Ohm), but then I got too low signal into and
out of the coil. May be, an aperiodic,low impedance output
amplifier would help. - But as now, the best I could do, was not
using coax-cable, but instead a "short as possible" 1.65m wire,
to connect the generator to the coil. This way the above
measurements were done. Probably, a number of list members have
noticed similar problems, or put it the other way: are you shure,
the measured resonant frequency is not distorted by connecting
your generator? I've experienced now, how sensitive and difficult
more precise solenoid measurements may prove, and would very much
welcome some comments on it from our experienced list members.
BTW: I'm happy to see, how the things now have reversed, and with
the exception of the small coil, Pauls predictions look more
close to the measurements :o)).
Cheers,
Kurt Schraner
*http://hot-streamer-dot-com/TeslaCoils/OtherPapers/MalcolmWatts/