On Jan 31, 9:38*pm, "Antonio Vernucci" wrote:
The answer may be in your own text (the ground issue). There may be a
third path via ground (capacitive coupling).

Hi Wim,

I acknowledege that your example leads to an asymmetric bipole, that one cannot
reverse it without consequences.

However, in the case which occurred to me, there is no need to assume the
existence of a third path via ground for justifying the asymmetry. Actually the
asimmetry remains even if the bipole would be in free space!

Forgive me if I do not immediately reveal my case, but I would like to see if
there are some more guesses before closing the issue.

73

Tony I0JX

as long as it is ONLY 2 ports, has ONLY passive linear components, AND
is small enough to be considered a lumped element, then you can always
reverse the terminals and not know the difference. The most
frequently violated condition is the last one, put in a piece of coax
with that is long enough to be measured at the highest frequency you
will use and all bets are off.

K1TTT wrote:


as long as it is ONLY 2 ports, has ONLY passive linear components, AND
is small enough to be considered a lumped element, then you can always
reverse the terminals and not know the difference. The most
frequently violated condition is the last one, put in a piece of coax
with that is long enough to be measured at the highest frequency you
will use and all bets are off.

An electrolytic capacitor acts differently if reverse biased. The results
are usually bad. It does qualify as two leaded, passive and linear when used
properly.

On Mon, 31 Jan 2011 17:23:33 -0600, joe wrote:

An electrolytic capacitor acts differently if reverse biased. The results
are usually bad. It does qualify as two leaded, passive and linear when used
properly.

Hi Joe,

The same can be said of a diode. Hence the electrolytic capacitor is
non-linear, which violates the premise.

73's
Richard Clark, KB7QHC

On Jan 31, 11:23*pm, joe wrote:
K1TTT wrote:

as long as it is ONLY 2 ports, has ONLY passive linear components, AND
is small enough to be considered a lumped element, then you can always
reverse the terminals and not know the difference. *The most
frequently violated condition is the last one, put in a piece of coax
with that is long enough to be measured at the highest frequency you
will use and all bets are off.

An electrolytic capacitor acts differently if reverse biased. The results
are usually bad. It does qualify as two leaded, passive and linear when used
properly.

an electrolytic that acts that way is not a linear component.

as long as it is ONLY 2 ports, has ONLY passive linear components, AND
is small enough to be considered a lumped element, then you can always
reverse the terminals and not know the difference.


You have pinpointed the correct issue: lumped elements.

The story began when, a few days ago, I was going to replace a trap of my HF
yagi. Not to make mistakes, I consulted the antenna assembly manual where I
found a big banner: do not invert traps otherwise the antenna will not work.

So, I thought, this is a case in which a bipole cannot be inverted.

This is clearly due to the fact that the external body of the trap (an aluminuim
can about 2 feet long), which contains two coils resonated at different
frequencies by means of built-in capacitors, is effectively part of the antenna
radiating element. So, the trap is a bipole not only comprising lumped elements,
and that is the reason why it cannot be inverted.

73

Tony I0JX
Rome, Italy

On Wed, 2 Feb 2011 09:35:38 +0100, "Antonio Vernucci"
wrote:

This is clearly due to the fact that the external body of the trap (an aluminuim
can about 2 feet long), which contains two coils resonated at different
frequencies by means of built-in capacitors, is effectively part of the antenna
radiating element. So, the trap is a bipole not only comprising lumped elements,
and that is the reason why it cannot be inverted.

Hi Antonio,

No, in fact.

You clearly state in the first sentence the reason why.

The external body renders an asymmetry. The two elements it separates
are also non-symmetrical (both physically and electrically).

This is NOT a lumped circuit exercise that has gone bad.

73's
Richard Clark, KB7QHC

As long as it is ONLY 2 ports, has ONLY passive linear components, AND
is small enough to be considered a lumped element, then you can always
reverse the terminals and not know the difference. The most
frequently violated condition is the last one, put in a piece of coax
with that is long enough to be measured at the highest frequency you
will use and all bets are off.

Could you please explain me the meaning of your sentence:

"put in a piece of coax with that is long enough to be measured at the highest
frequency you will use and all bets are off"

as I have difficulties to interpret it due to my non-mother tongue english.

73

Tony I0JX
Rome, Italy

On Feb 1, 6:24*pm, "Antonio Vernucci" wrote:
As long as it is ONLY 2 ports, has ONLY passive linear components, AND
is small enough to be considered a lumped element, then you can always
reverse the terminals and not know the difference. *The most
frequently violated condition is the last one, put in a piece of coax
with that is long enough to be measured at the highest frequency you
will use and all bets are off.

Could you please explain me the meaning of your sentence:

"put in a piece of coax with that is long enough to be measured at the highest
frequency you will use and all bets are off"

as I have difficulties to interpret it due to my non-mother tongue english.

73

Tony I0JX
Rome, Italy

the general case is, if any part of the circuit is more than a small
fraction of a wavelength in size you may be able to detect the
difference between the ports. one common way to do that is to try to
measure a circuit that has a long piece of coax in it, the results may
be very different when you reverse the terminals.