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Post by ajaques on Mar 18, 2016 4:03:50 GMT -5
Hi all, I have an AIM 4170C and a problem that I hope is just me being dim! On a wideband sweep with a very small step size 0.01MHz or so the result is a totally yellowish graph area - but only when Rp/Xp is "turned on". Without that the display is normal. The bigger the step size is the clearer the display becomes. With a 0.5MHz step the effect nearly disappears. But this is a rather large step size for many measurements. I have "attached" two images to show the effect. Has anyone else seen this? Is it a consequence of making the AIM accept unreasonable settings? Or do I have a problem with the unit? Or (as I implied) is it much brighter than I? Tony (G3PTD) Attachments:
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Post by Bob on Mar 18, 2016 10:42:01 GMT -5
Hi Tony,
This is a normal condition when scanning a low impedance. The phase angle can change from +90 to -90 degrees very rapidly.
This just indicates the parallel equivalent circuit is not useful for this impedance and it is better to use the series circuit. Mathematically they are equivalent but the display can be confusing when the phase changes from + to - so quickly.
In general the parallel circuit is more useful when the magnitude of the impedance is large. It is especially interesting to scan a large resistor, like 1K ohm, and see the value of the equivalent capacitance that is in parallel with the resistor. You will see the value of Zmag decreases with frequency because the reactance of this cap decreases but the value of Rp is nearly flat at the 1K level.
When you change the parameter that is plotted, you don't have to rescan the component. The original measured data is still in memory and that is used again for the new plot.
73/Bob - W5BIG
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Post by ajaques on Mar 19, 2016 2:39:07 GMT -5
Thank you very much for the reply Bob.
That was very helpful, and of course I see it - now that
someone else has pointed it out!
I shall do the experiments that you suggest. I have already
been amazed by the way that reactive components can't be trusted
as soon as the frequency goes beyond audio, so I am sure that
I will find it interesting.
Tony (G3PTD)...
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