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The calculation is simple, but the concept of impedance is not always easy.
Few radio amateurs without an engineering background ever figure this stuff out completely.

Impedance is like resistance, but adds the complication of phase.
To keep the formulas simple we use "complex numbers".


Normal "real" numbers only have one dimension, along the number line.
Complex numbers have a second dimension perpendicular to the real axis.
Weirdly enough, the math all works out beautifully if we assume the perpendicular axis
has units of the square root of -1, often expressed with the symbol j.

Once we express impedances as complex numbers, we can use the same formulas
to combine impedances as we do for resistors.

Ohm's law still works too, divide an AC RMS Voltage by and impedance and?
you get a current in Amps, where all three values are complex numbers.
The phase of the complex number for the current will be shifted with respect to
the phase of the voltage, exactly as?you would see with an oscilloscope.



Lets assume the 45mhz filter does have an input impedance of 650 ohms?
in parallel with 3pF as Gerard shows in his diagram.
The 3pF is in parallel with the 22pF of C212, resulting in 25pF of capacitance.
The formula for the impedance of an inductor is zL = j * 2*pi*f * l)
where f is the frequency in Hz and l is the inductance in Henries.
The formula for the impedance of a capacitor is zC = 1/(j * 2*pi*f * c)
where f is the frequency in Hz, c the capacitance in Farads, and zC the impedance in ohms.

That capacitive impedance is in parallel with the 650 ohms resistance,
which can be calculated as:? ?zP = zC*650/(zC+650)
And that impedance in series with the 720nH inductor L7 is zIN = zL + zP

Python is a simple programming language that knows about complex numbers,
We use exponential notation for the big and small numbers, so 720e-9 is 0.000000720
We can write this up as a python script:
On Mon, Mar 25, 2024 at 01:02 PM, ajparent1/kb1gmx wrote: