On 31 ene, 21:20, "Antonio Vernucci" wrote:
Yesterday, while repairing my antenna, something came to my mind I had never
focused on before.

Let us consider a bipole, that is a "black box" having TWO terminals and
including plain passive elements only (like capacitors, inductors, ... , no
diodes or other special devices), arranged the way you prefer, it does not
matter.

In my mind it was quite clear that, when fitting such a bipole into a circuit,
the sense makes no difference, i.e. one can reverse the two terminals with no
consequence. As a matter of fact, the bipole has an equivalent impedance that
remains the same independently of the way it is put in the circuit.

Yesterday a case occurred to me in which this is not actually true.

Instead of directly telling which it is, just for fun I wonder whether anyone
can figure out a case in which a bipole may not be reversed without
consequences. Not difficult, but it anyway requires some thinking.

Although probably unnecessary, let me recall that a filter is typically a
THREE-terminal device (IN, OUT, GROUND), not a TWO-terminal one.

73

Tony I0JX
Rome, Italy

Hello Tony,

The answer may be in your own text (the ground issue). There may be a
third path via ground (capacitive coupling).

You can add a very good common mode choke at the input terminal of you
bipole. In that case the path via ground is blocked.

Try a very simple bipole: metallic case connected to terminal 1,
terminal 2 connected to nothing. When the center conductor of your
source is connected to terminal 1, you have the ground path.

The effect of reverse connection will be less when you use a very
small battery powered source that is completely floating. Measuring
data you can get out of it via optical link...

Best regards,

Wim
PA3DJS
www.tetech.nl
without abc, PM will reach me.