On Mon, 21 Oct 2002, Jim wrote:

*>Peter, I don't know *why* you need a phase-capable
*>indicating system for use with a bridge - when
*>a simple 'detection' (diode, meter, etc) will
*>suffice to detect 'the null' when the bridge
*>has reached the balanced state ... a simple
*>diode RF detector outfitted to your favorite
*>DVM can provide that function ...

*>Between what two points do you hope to view
*>the phase and what information might this reveal?

I want to be able to use it to measure/balance complex RLC loads like
transformer + cable + transformer or telephone line equivalent or resonant
transducers and other such things. Otherwise I would not bother.

*>As to needing 'extra pairs of scope probes' for
*>a scope for to be used in a particular dedicated
*>application - I would suggest the use of 'resistive
*>dividers' in the manner of 'minimum-loss matching
*>pads' (or even the use of buffer amplifiers!)
*>designed placed at the output of the DUT (or test
*>set) and 50 (or 75 or 93) Ohm cable routed for display
*>on  the O-scope where said cable is terminated in
*>it's characteristic Z. Many newer/high frequency
*>scopes also have a termination selection built-in.

Yes except @home I use an old 2 x 25MHz scope. Buffer amplifiers could be
used, good idea. Now all I have to do is match them in phase and
compensate for any distortion they may induce (when is an ellipsis an
ellipsis, and where are its apexes ? ;-).

*>The point being, the lowly O-scope should not be
*>overlooked for some of the more slightly exotic
*>applications such as observing phase and magnitude
*>of two signals ...

That is correct but squinting at a trace and using a ruler or protractor
or something like that on a 5 inch screen with more than enough parallax
is less elegant and less accurate than reading a pair of DVMs. The DVM
'vector voltmeter' would also be portable more or less.

I think I tried to use my home scope only once in XY mode and I got a
'snake' curve from connecting both channels to a sine wave source. Needs
linearity calibration (I doubt it has such a control) or junking ;-).
Remember on cheap scopes the X and Y amplifiers are built very different.

Peter

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