From: Kurt Schraner
Date: Sat, 16 Jun 2001 12:00:37 +0200
Subject: Re: [TSSP] Short Coil Experiments
Paul, thank you! Below, interpersed, a few additional comments to the measurements. Paul wrote: > > Kurt wrote: > > > the new measurements of the d=0.385m; h/d=1.15 > > Thanks. I've run these through the mill to get > > sk38b50: bare d=0.384m h/d=1.15 sr=0.79 turns=346 w/o mat > f1 221.3kHz 230.1kHz +4.0% > f3 506.5kHz 557.2kHz +10.0% > f5 748.8kHz 882.5kHz +17.9% > f7 831.0kHz 1222.5kHz +47.1% > > without any correction for material dielectric. > > (Kurt, the f7 measurement is suspicious - I'd expect something > around 980 kHz. I see you flagged it as questionable.) > This measurement was nothing more than a just distinguishable change of appearence of the scope trace (very small amplitude), at roughly the indicated frequency. It should be discarded; better I was not even including it in the results-table! > The rising trend in errors is clear, and similar to what we have seen on > other coils, eg Finn's> If we take the material thickness as a percentage of the length, we get > Kurt's: 0.8/44 = 1.8% > Finn's: 0.55/14.5 = 3.8% > which we can use as an indication of the potential effect of the former. > I put in a rough correction for this, which came out with the right sort > of order of magnitude of change, which is encouraging. It also improves > the results from larger h/d coils too, where the rising error trend is > still present, but less, eg Kurt's Sk-long coil:> > If we put in an approximate correction for the 3mm PVC, we get > > sk16b50: bare d=0.161m h/d=8.71 sr=0.85 turns=1976 matcor > f1 152.3kHz 155.3kHz +1.9% > f3 387.2kHz 382.4kHz -1.2% > f5 564.2kHz 557.8kHz -1.1% > f7 713.0kHz 708.4kHz -0.6% > f9 850.0kHz 845.0kHz -0.6% > f11 973.3kHz 972.9kHz -0.0% > > which suggests that the correction is not quite enough. The f1 point might be low, because of surrounding's influence on this tall coil. Otherwise, I believe, my results are (-in absolute terms-) not more precise, than your calculations. > > Kurt, you also supplied results for Sk-5cm, > > sk5b503: bare d=0.051m h/d=8.03 sr=0.91 turns=934 w/o mat > f1 979.7kHz 1030.8kHz +5.2% > f3 2428.7kHz 2531.9kHz +4.3% > f5 5300.0kHz 3707.7kHz -30.0% > f7 6924.6kHz 4739.0kHz -31.6% > f9 8643.1kHz 5694.6kHz -34.1% > > Something a bit astray with f5 and above. I get a better match if I > interpret the results as: > > sk5b503: bare d=0.051m h/d=8.03 sr=0.91 turns=934 w/o mat > f1 979.7kHz 1030.8kHz +5.2% > f3 2428.7kHz 2531.9kHz +4.3% > f5 3707.7kHz > f7 4739.0kHz > f9 5300.0kHz 5694.6kHz +7.4% > f11 6605.9kHz > f13 6924.6kHz 7502.1kHz +8.3% > f15 8384.8kHz > f17 8643.1kHz 9272.9kHz +7.3% > > > Kurt, perhaps you can have a look for the missing resonances? > I'll do that. But for the moment I just like to mention, the Heathkit RF-generator has much lower quality, than the Siemens. I've recognized a strongly distorted output signal (something like triangular, instead of sine). On one of the harmonics (5300kHz?) it was generating an nonsine antenna-signal, like 2 interfering sines. I had to use this generator, 'cause the Siemens only goes to 1.6 MHz. I also got higher peaks (13.68MHz, 17.245MHz), which I'm no more shure, if they don't represent resonances of different origin, than just the coil... > One last observation, concerning Q factors: The Q of Kurt's sk38b50 > is very low, around 100, compared with a predicted Q of well over 500. > Is this the sonotube effect we see here. My book on dielectric > properties gives the loss factor of paper/cardboard as 0.02, which is > abysmal. > If the Generator-Z was really low, the measured Q should not be too far away from reality. Of course the 70.7% max.-amplitude reading on the scope is not very precise, perhaps 68..73%. But, as mentioned in my last mail, I'm not very shure about the generator-impedances. > I'll see if I can use a laplace solution to improve the material > correction, but so far it sure looks like it can account for the bulk > of the higher mode error. > > Cheers, > -- > Paul Nicholson, > Manchester, UK. > -- Cheers, Kurt
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.