On Feb 1, 3:24*pm, K1TTT wrote:
On Feb 1, 6:18*pm, K7ITM wrote:



On Jan 31, 12:20*pm, "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

I have a circuit I've been working on lately which has a simple series
LC in it, no other connection to the node between the inductor and
capacitor. *It turns out that the order of the inductor and capacitor
makes a big difference in the circuit performance. *I anticipated that
it would, and put them in the intuitively obvious order, only to find
out that it was the wrong order! *A proper model cleared things up
quite nicely. *However, in no way would I call that particular part of
the circuit a "two terminal" network. *The effect is the same as Wim
mentioned.

Cheers,
Tom

then there is either something wrong with your components or you have
too much coupling the the surrounding environment...

If by "too much" you mean "more than I wanted," you're absolutely
right. But of course with real components, there is no such thing as
zero coupling to the surrounding environment. As with all real
circuits, there are tradeoffs: high coil Q results in a large coil,
which in turn results in more capacitance to the shield than a smaller
low-Q coil would have. The shield is required for other reasons...

... so you really had
a 3 terminal network using the stray capacitance or inductance.

Exactly. Just what I said: the effect is the same as Wim mentioned.

Cheers,
Tom