From: "Terrell W. Fritz"
Date: Tue, 16 Jan 2001 18:29:31 -0700
Subject: Re: [TSSP] Top voltage testing
Hi Malcolm, It appears that the variation in frequency is due solely to the capacitance of the probe while the variation in Q is due solely to the resistance of the probe. Thus, it is pretty easy to figure out the effect of the probe loading. I was playing with models of this. What is odd is that the bandwidth Q and the voltage rise Q are always the same in the simple lumped element models. Paul's more advanced program is needed to explain the difference in the Q's that I see in actual measurements. Cheers, Terry At 02:29 PM 1/16/2001 +1300, you wrote: >Hi Terry, > The 10 MOhms is the problem. It will be hitting the Q >measurement for sure. Suppose Zo is about 30k. Then matching >impedances are about 40k for each end. Zo^2 = 9e^8. Suppose you >terminate one end of the coil with 100 Ohms. The other end will have >an equivalent shunt Z approaching 9 MOhms and the problem just gets >worse as the termination value goes down. This is typical 1/4 wave >line stuff and makes measurements a nightmare. No problem if the line >is RG58 etc. In fact, this is probably what made some of the Corum's >coils look so bad (e.g. Q of 60 for a large spacewound coil which I >reckon should have been at least 300). > >Regards, >malcolm > >> The probe bothers me too but Paul seems to think it works. The probe >> is 10.0Meg ohm 16.6pF. Also, the wire to the probe must really make >> some wild bends and disturbances in the fields around the coil. I >> think Paul accounts for this in his computer model but I don't >> understand it all well enough to know how. I don't quite see how I >> would calculate this but let me know what to do and I'll do it. >> >> Cheers, >> >> Terry > >
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.