## Toro MX 4250 starter current captured using a Picoscope

A recent exercise was to become familiar with a recent acquisition, a Picoscope USB oscilloscope.

It has quite different software to those of other USB oscilloscopes that I have used, so a bit of learning and adaptation.

The test scenario here is capture of battery current and battery voltage whilst cranking my lawnmower which as a 24.5HP V twin petrol engine. Above is the captured data expanded to explore the initial part of cranking (with disconnected spark plugs). Continue reading Toro MX 4250 starter current captured using a Picoscope

## Determination of transmission line characteristic impedance from impedance measurements – eighth wave method

For a lossless line, the reactance looking into short section and open circuit terminated line sections is $$X_{sc}=Z_0 \tan \beta l$$ and $$X_{oc}=Z_0 \frac1{\tan \beta l}$$.

Noting that when $$\beta l= \frac{\pi}{4}, \tan \beta l=1$$ so when the line section is π/4ᶜ or 45° or λ/8, then $$|X_{sc}|=|X_{oc}|=Z_0$$.

We can use this property to estimate Z0 of an unknown practical low loss transmission line by finding the frequency where $$|X_{sc}|=|X_{oc}|$$ and inferring that $$Z_0 \approx |X|$$. Above is a chart created using Simsmith’s transmission line modelling of the reactance looking into short section and open circuit terminated 10m sections of RF174. The blue and magenta lines intersect at X=51.16Ω whereas red R0=51.85Ω, about -1.3% error. The error depends on line loss, line length, frequency and the characteristics of the terminations. Continue reading Determination of transmission line characteristic impedance from impedance measurements – eighth wave method