Original poster: "Kurt Schraner" <k.schraner@xxxxxxxxxxx>
Hi Bart,Gerry,
Medhurst's empirical Method for HF-Resistance of solenoids is
implemented in my TC-Plan Excel:
http://home.datacomm.ch/k.schraner/TCplan.zip
The relevant sheets are "Skineff." and "Proxi-eff.", whose results are
transferred to "TC calc."' cells E34:E38. In the light of more up to date,
more general methods, Medhurst may soon become of lesser relevance,
but I've tried to compare results from it, with Q of some of my
coils, estimated from bandwidth measurements at Fres. A summary
Excel of the results can be had at:
http://home.datacomm.ch/k.schraner/Qsec2.xls
or here (view in fixed width font, sorry for the possible mess!):
TC-Secondary Q-Estimation by Medhurst's Empirical Method
for some of my Coils
Geometric Data
Secondary Diameter Length Aspect L/D Turns
Name [cm] [cm] [ - ] [ - ]
Sk-Seibt 4 150.3 37.58 4187
Sk-UBTT 12.54 60.3 4.81 1680
Sk-5cm 5.11 41.1 8.04 934
Sk-12cm 12.12 58.5 4.83 894
Sk-Long 16.1 140.2 8.71 1976
Sk-20cm 20.52 66.8 3.26 943
Sk-38cm 38.4 44 1.15 346
Sk-B&W *)40.13 177 4.41 813
Sk-B&W *)40.13 177 4.41 813
Geometric Data (cont.)
Secondary Wire-Copper Pitch Comment
Name [mm] [mm]
Sk-Seibt 0.319 0.359 Big error unexplained!
Sk-UBTT 0.319 0.359 Test-signal via low-Z amp.
Sk-5cm 0.4 0.434 no experiment
Sk-12cm 0.6 0.654 Test-signal via low-Z amp.
Sk-Long 0.64 0.71 Test-signal via low-Z amp.
Sk-20cm 0.63 0.708 no experiment
Sk-38cm 1 1.2 cardoard/cotton insul. wire
Sk-B&W *) 1.268 2.177 Test-signal via low-Z amp.
Sk-B&W *) 1.268 2.177 if R Sig-Gen=136 Ohm
Electrical Data
Secondary at1kHz Fres,bare DC Resist. Wire straigt
Name Lexp[mH] exp.[kHz] exp.[Ohm] with Skineff.
Sk-Seibt 18.13 366.11 114 240.82
Sk-UBTT 66.59 205.4 147.8 147.86
Sk-5cm 5.203 923.8 21.7 n.a.
Sk-12cm 18.2 402.8 21 27.61
Sk-Long 67.7 147.4 55.2 61.05
Sk-20cm 49 202.7 34.8 40.5
Sk-38cm 28.12 217.95 9.2 16.32
Sk-B&W *)54.67 119 14.5 22.3
Sk-B&W *)54.67 119 14.5+136 22.3+136
Electrical Data (cont.)
Secondary Rac-calc. Qexp Qmedh. Qerror
Name with Proxy.E [ - ] [ - ] [%]
Sk-Seibt 698.9 156.5 70.8 54.8%
Sk-UBTT 440.65 211.8 186 12.2%
Sk-5cm n.a. n.a. n.a. n.a.
Sk-12cm 91.01 269 270 -0.4%
Sk-Long 190.6 164.4 168.4 -2.4%
Sk-20cm 128.0 n.a. 478.3 n.a.
Sk-38cm 49.79 104.3 803.7 -670.6%
Sk-B&W *) 44.02 141.7 576 -306.5%
Sk-B&W *) 44.02+136 141.7 141.7 0.0%
The method seems to underestimate Q of my small diameter coils, and to
(heavily) overestimate the Q of the big diameter coils. What seems obvious
is the dominant proximity effect over skineffect for usual TC frequencies,
as mentioned before on the relevant treads. Maybe dielectric loss, not
considered in the calculations, come to play here...
*) For the bandwidth measurements it seems important using a low-Z signal
source (--> Terry's low-Z amp), which was not the case for "Sk-B&W".
Otherwise the generators internal resistance will reduce measured Q value.
Anyway, bandwidth measurements seem prone to higher error, 'cause of
amplitude reading on the scope and frequency precision reading from the
sig-gen.
Well ... my 2cents for the interesting threads about coil Q. If I
see coming out a method estimating Q with perhaps 10% error, I'd
readily adapt it!
Best regards
Kurt