From: "Terrell W. Fritz"
Date: Tue, 02 Jan 2001 20:35:03 -0700
Subject: Re: [TSSP] NSVPI - Terminated Coil Results
Hi Paul, At 10:46 AM 1/2/2001 +0000, you wrote: >Terry, All, > >You might like to try the following modification to the NSVPI >gradient probe, in attempt to get it to work without requiring >electrical contact with the coil. The idea is to add in an RF >choke to provide a DC path for the diode to charge the storage >cap. > > | pt > | ----||--- <-------------[diode]-- > | pc | | > | | | >sec | -[choke]- --- storage cap >coil | | --- > | pt | | > | ----||--- <---------------------- > | pc > | > >'pc' are the 'contact capacitances' of the two probe terminals 'pt', >[choke] is an RF choke wound on a miniature toroidal ferrite >core - this so that inductive coupling with the secondary is >minimised. Alternatively, use a high value resistance instead, and >allow time for the storage cap to charge. Originally, I tried this as shown at: http://hot-streamer.com/TeslaCoils/Misc/PaulNich/oldNSVPI.jpg It seemed the contact capacitance was so small (perhaps compared to the diode's junctions capacitance) that it would not charge. I just didn't seem to be able to get the diode to charge the cap even with germanium diodes. The junction just would not conduct. Would the chock help this?? > >We could do to figure out a way to make an absolute top volts >measurement. Terry's toroided coil Q of 164 gives a predicted >voltage gain of 168.5, but the cumulative gradients, with 0.12 >diode drop added, gives around 155 volts, so we have a discrepancy >here which appears larger than either the measurement or prediction >errors. > >Note that for the bare coil case, Q=60, Vgain predicted is 68.5 >and the cumulative voltage was 69.72 - within limits. > I think I just need to fix the ground plane again and drop a scope probe down onto the top of the coil. I have a 3pF 1000:1 probe that should do minimal loading both from capacitance and resistance. It also has a real long cable. It will add some C to the top and change Fo a little but maybe that won't be a problem. I assume both toroid and non-toroid cases are wanted. Time is short tonight, but I'll try tomorrow. Let me know if that is what you had in mind? Cheers, Terry >Cheers, >-- >Paul Nicholson, >Manchester, UK. >--
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.