From: Paul
Date: Sun, 04 Feb 2001 07:35:43 +0000
Subject: Re: [TSSP] 50 ohm Generator hookup
Terrell W. Fritz wrote: > My 777pF long coax did add significant loading :-)) Gosh, that's a lot! Isn't that about 25 metres of thin coax? > What I found is that when the primary and secondary of the > transformer are wound directly over each other as in this > transformer, there is significant primary to secondary > capacitance which wreaks havoc on the measurement circuit > in this case. Indeed. I assumed you'd use a toroidal flyback ferrite and put the windings diametrically opposite each other. Mine has only 8pF between primary and a bifilar secondary, which is not enough to interfere with the relatively low impedance measurements around the coil base. With the windings stacked on top of each other I should think you'd get a few hundred pF, which would be troublesome. BTW, I use a bifilar secondary in which the second secondary is wired in reverse to a potentiometer in such a way that the thing acts as a bridge. I use it to get quick base impedance measurements by switching out Rs, driving in through the 'current' port and adjusting the pot for a dip in the signal from the 'drive' port. Cheers, -- Paul Nicholson, Manchester, UK. --
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.