Cecil Moore wrote:

Old Ed wrote:
"Lossless resistance?" Would that be zero resistance,
or perhaps a negative resistance, as in the active part of
a tunnel diode's V-I characteristic?

I am a career EE, with a couple of graduate EE degrees;
and this is something entirely new to me. Could you explain
this concept, and/or provide some references?

How about an example? If L and C are lossless, then SQRT(L/C)
will be lossless with a dimension of ohms, i.e. resistance.

Umm, isn't that an example of reactance? I assume you would have us
believe they are one in the same. BTW, not all forms of resistive loss
are "ohmic".

73, Jim AC6XG
73, Jim AC6XG

Jim Kelley wrote:
BTW, not all forms of resistive loss are "ohmic".

The SQRT(L/C) of a lossless transmission line is certainly "ohmic".
Or are you willing to assert that the Z0 of coax is really j50 or
some such. May I suggest a good book on dimensional analysis?
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil Moore wrote:

Jim Kelley wrote:
BTW, not all forms of resistive loss are "ohmic".

The SQRT(L/C) of a lossless transmission line is certainly "ohmic".

You don't seem to know what the term "ohmic" means.

73, Jim AC6XG

Jim Kelley wrote:

Cecil Moore wrote:
The SQRT(L/C) of a lossless transmission line is certainly "ohmic".

You don't seem to know what the term "ohmic" means.

From the IEEE dictionary: "ohmic contact ... one that has a linear
voltage/current characteristic throughout its entire operating range."
That certainly seems to describe the characteristic impedance of a
transmission line which has a linear voltage/current characteristic
throughout its entire specified operating range even though that Z0
is non-dissipative.

I'm assuming anything with the dimensions of "ohms" is "ohmic" but
I could be wrong. Do you have a reference otherwise?
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil, W5DXP wrote:
"I am assuming anything with the dimensions of "ohms" is "ohmic" but I
could be wrong."

That would apply to a transmission line where "The characteristic
impedance Zo is the ratio of voltage to current in an individual
wave;---it is also the impedance of a line that is infinitely long ---"
or terminated in ZL = Zo.

As Reg once noted, you could measure Zo with your ohmmeter in an
infinite line.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
Cecil, W5DXP wrote:
"I am assuming anything with the dimensions of "ohms" is "ohmic" but I
could be wrong."

As Reg once noted, you could measure Zo with your ohmmeter in an
infinite line.

But some people play semantic games. The IEEE dictionary generally
avoids definitions of adjectives and favors adjectives plus nouns,
e.g. "ohmic contact".

From my physics book, an ohmic conductor is one whose resistivity
is constant with changing voltage. Does "resistivity" imply dissipation?
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil, W5DXP wrote:
"Does "resistivity" imply dissipation?"

I haven`t looked it up but the word "resistivity" automatically
generates a definition in my mind:

Rho = length / area.

Best regards, Richard Harrison, KB5WZI

As Reg once noted, you could measure Zo with your ohmmeter in an
infinite line.

===========================

It would not be a steady reading on the ohmeter. It would be a quick
deflection followed by a slower subsidence.

Zo of real lines is a function of frequency. As frequency decreases Zo
increases and becomes more reactive ultimately approaching -45 degrees.
This affects in a complex manner the behaviour of the ohmeter pointer.

The ohmeter reading changes from an initial low value to a higher value
versus time. The actual values and time taken depend on Zo and on the
voltmeter resistance. The final value is never achieved just as the final
voltage across a capacitor being charged up via a resistor is never
achieved.

To calculate input resistance versus time as recorded on the ohmeter
requires a large amount of calculation using Heaviside's operational
calculus.

An infinite series of complicated terms is involved. This type of
calculation on transmission lines must have been amongst the very first
carried out by the young Heaviside himself round about 1872. It is closely
related to the distortion of keying waveshapes along telegraph cables.
Imagine the pleasure he experienced, using his own calculus, as he with his
sliderule produced the very first sets of figures and graphs describing the
waveshapes. It is still related to distortion of digital signals in this
modern electronic age but now we have oscilloscopes.
----
Reg, G4FGQ

Jim, AC6XG wrote:
"Ummm, isn`t that an example of reactance?"

Terman on page 88 of his 1955 edition says:
"The characteristic impedance Zo is the ratio of voltage to current in
an individual wave---; it is also the impedance of a line that is
infinitely long or the impedance of a finite length of line when ZL =
Zo. It will be noted that at radio frequencies the characteristic
impedance is a resistance that is independent of frequency."

Isn`t that succinct and beautiful? Wish my thoughts were as clear and
true. We lost a treasure when he passed away.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:

Jim, AC6XG wrote:
"Ummm, isn`t that an example of reactance?"

Terman on page 88 of his 1955 edition says:
"The characteristic impedance Zo is the ratio of voltage to current in
an individual wave---; it is also the impedance of a line that is
infinitely long or the impedance of a finite length of line when ZL =
Zo. It will be noted that at radio frequencies the characteristic
impedance is a resistance that is independent of frequency."

Isn`t that succinct and beautiful? Wish my thoughts were as clear and
true. We lost a treasure when he passed away.

Absolutely. If only it were as relevant as it is succinct and
beautiful. But, that's a little out of Terman's hands at this point.
;-)

73, Jim AC6XG