Re: Scoping of Secondaries
Subject: Re: Scoping of Secondaries
From: "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz>
Date: Sun, 17 Dec 1995 12:24:36 +1200
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On this subject, Steve writes...
> 1. You should turn all your equipment on and let it warm up for at least
> 1/2 to 1 hour before using it. I was sitting there watching my frequency
> generator change frequency by a few Hz every couple seconds for
> quite a while after I turned it on.
> 2. Series resistance does make a difference. I have a 0-10 mHz
> Hewlett Packard signal generator that has 75 ohm and 600 ohm
> outputs. When I used either the 600 ohm output from the signal
> generator or the cable that has the 1K resistor wired in series , I
> measured Q's in the neighborhood of 30-50. When I used the 75 ohm
> output with a regular RG59 coax cable and no series resistor, I got a Q
> of 200.
You'll shortly see some data measured using a near voltage source.
> This raises some other questions. I'm assuming that a signal
> generator with an even lower impedence would give an even more
> accurate value for Q, but since I have what I have, is there any way to
> compensate for this resistance? Also, rather than just believing the
> label that says 75 ohms by the output jack, what can I do to confirm or
> compute the actual impedence of my signal generator? Would I be
> able to measure the open circuit voltage and the short circuit current (at
> say, 60Hz) and use these values to calculate the internal resistance, or
> is there something more complicated involved?
(a) Add a buffer amp (I've outlined my generator design in the post.
(b) Measure drops into various impedances (L,C, and R) at different