On Feb 2, 3:42*am, "Antonio Vernucci" wrote:
Tom,

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.

So, as K1TTT has pointed out, a bipole can be inverted without consequences only
if it has only 2 ports, has only passive linear components, and is small enough
to be considered a lumped element.

73

Tony I0JX
Rome, Italy

A bipole is symmetrical, obviously the internal circuity of the trap
is not symmetrical .

Jimmie

A bipole is symmetrical, obviously the internal circuity of the trap
is not symmetrical .

Jimmie, that is not the point.

- if the bipole is made of lumped components, then it can be freely reversed
without consequences, independently of whether it is symmetrical or asymmetrical

- a trap, which instead contains a distributed element (that is the radiating
trap body), can be freely reversed without consequences only if it is
symmetrical (which is not my case).

73

Tony I0JX

Hello Tony,

On 2 feb, 19:14, "Antonio Vernucci" wrote:
A bipole is symmetrical, obviously the internal circuity of the trap
is not symmetrical *.

Jimmie, that is not the point.


At some frequency, everything becomes a distributed component, it
depends on size/lambda ratio and application. Many distributed
components can be modelled based on theoretical lumped components
(with sufficient accuracy), but a ground for modelling stray
capacitance is frequently required.

True lumped component behaviour, in my opinion, only applies to
networks with size=0.

- if the bipole is made of lumped components, then it can be freely reversed
without consequences, independently of whether it is symmetrical or
asymmetrical

What do you define as "lumped component"?

- a trap, which instead contains a distributed element (that is the radiating
trap body), can be freely reversed without consequences only if it is
symmetrical (which is not my case).


I agree on the above.


73

Tony I0JX

Best regards,


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

On Feb 2, 12:42*am, "Antonio Vernucci" wrote:
Tom,

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.

So, as K1TTT has pointed out, a bipole can be inverted without consequences only
if it has only 2 ports, has only passive linear components, and is small enough
to be considered a lumped element.

73

Tony I0JX
Rome, Italy

As I see it, it has nothing to do with being small enough to be
considered a lumped element. Instead, it has to do with coupling
between the network elements and the outside world. Clearly your
trap is coupled to the outside world. Clearly the series LC in my
example is coupled to its surroundings. In such cases, you're NOT
dealing with a two-terminal network: there is a path for current
other than the two terminals. You can put as many transmission lines
in your network as you wish, and as long as they don't have coupling
to the rest of the universe except through the two closely-spaced
terminals, there will be no difference in behaviour if you reverse the
terminals. If you can show a valid counter-example, you've proven a
whole lot of textbooks wrong...

I suppose equivalently, if you decouple your measurement from the rest
of the universe, you'll get the same result. Typical broadband
directional couplers (of the sort used in S-parameter test sets) have
good decoupling, to be able to separate excitation from return power.

Cheers,
Tom

In my first EE class, 'way back in the fall of 1962, the instructor
walked in and said "We shall study LLFPB", by which he meant

Lumped, Linear, Finite, Passive, and BILATERAL

so I'd have to conclude that your bipole is one or more of
not lumped and/or
not linear and/or
not finite and/or
not passive.

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.

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.
--
-- Myron A. Calhoun.
Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge
NRA Life Member & Certified Instructor for Rifle, Pistol, & Home Firearm Safety
Also Certified Instructor for the Kansas Concealed-Carry Handgun (CCH) license