"Owen Duffy" wrote in message
...
Well, we all like Distortionless Lines, almost all ham discussion
and indeed much if not most textbook discussion is about one
special case of a Distortionless Line, the Lossless Line.

Nevertheless, we apply one property of Distortionless Lines to
real lines, the property that Zo=Ro+j0, and that Zo is independent
of frequency.

Or, in other words, the Heaviside Condition is met.

C/G = L/R

This is met in lossless lines with R and G being zero, and the
characteristic
impedance being real.
_____________________ _____
Zo = v((R + j?L)/(G + j?C)) = v(L/C)

But, a real Distortionless Line (real excludes Lossless) doesn't
have much application for us.

Consider that with real inductors and capacitors, the permeability,
µ, and the permittivity, e, are themselves often complex.

µ = µ' + jµ" and e = e' + je"

Of the two, I am most familiar with dielectric properties of
polymers as a function of frequency. With plastics like
polyethylene and polytetrafluoroethylene, e' (the real part) remains
fairly constant from low frequencies well into the microwave region,
and e" (the imaginary part) is quite low. Plastics like
polyvinylchloride, on the other hand, show an increasing e" with
frequency due to rotational hindrances of strong dipoles in the
polymer.

Similar frequency dependencies are seen at optical frequencies,
where the refractive index is a function of wavelength. Chromatic
aberration, the failure of a lens to focus all colors to the same
point, is caused by this change of refractive index with
wavelength. In general, the refractive index of a material
increases with increasing frequency. In the infrared and visible
portions of the spectra, we see large changes in permittivity
because of vibrational resonances in the polymer groups.

Though I haven't had my hands on a Distortionless Line, it occurs
to me that increasing L/m is a means of diminishing the effect of
changing R/m, making G/m higher is another means of making Zo
real, and if the materials make R/m(f) track G/m(f) closely ...
then the problem is mostly solved.

With typical commercial coaxial cables, the ratio of shunt
conductance to shunt capacitance is generally much lower than the
ratio of series resistance to series inductance (all per unit
length). This makes the characteristic impedance complex, and the
cable causes distortion.

In the weird cable I described earlier, the resistance of the wire
would increase linearly with the number of turns per unit length but
the inductance would increase as the square of the turns per unit
length. So there would be merit here. Increasing the shunt
conductance will also help — at the expense of making the cable
extremely lossy.

While we have been talking about conventional electrical
transmission lines, we can also analyze nerves as a transmission
line. A nerve is essentially an electrical transmission line with
chemical transducers on each end. When a receptor synapse detects
a neurotransmitter, like serotonin or norepinephrin, it sends an
electrical signal down the neuron. The neuron is the transmission
line. It is essentially an ionic conductor covered with a fatty
substance known as myelin. The result is a distributed resistance-
capacitance line. In diabetics, the myelin sheath is partially
destroyed and replaced with sorbitol, a sugar alcohol. In addition
to being more conductive than myelin, sorbitol has a far higher
dielectric constant. Viewing the neuron as a distributed RC line,
we have both added shunt conductance and increased the capacitance.
It is no wonder that nerve conduction velocity and amplitude both
decrease resulting in such things as peripheral neuropathy, usually
associated with diabetics.

--
73, Dr. Barry L. Ornitz WA4VZQ

"Dr. Barry L. Ornitz" wrote in news:qmxIl.84715
:

....
While we have been talking about conventional electrical
transmission lines, we can also analyze nerves as a transmission
line. A nerve is essentially an electrical transmission line with
chemical transducers on each end. When a receptor synapse detects
a neurotransmitter, like serotonin or norepinephrin, it sends an
electrical signal down the neuron. The neuron is the transmission
line. It is essentially an ionic conductor covered with a fatty
substance known as myelin. The result is a distributed resistance-
capacitance line. In diabetics, the myelin sheath is partially
destroyed and replaced with sorbitol, a sugar alcohol. In addition
to being more conductive than myelin, sorbitol has a far higher
dielectric constant. Viewing the neuron as a distributed RC line,
we have both added shunt conductance and increased the capacitance.
It is no wonder that nerve conduction velocity and amplitude both
decrease resulting in such things as peripheral neuropathy, usually
associated with diabetics.

I contracted a disease when I was young, a disease that caused the body's
T cells to attack the cells of the mylon sheath (in our terms, the
dielectric that separates the =ve and -ve ionic material in the nerve's
coaxial cable, effectively shorting the coax.

During a week or two of onset of the disease, the doctors performed TDR
like tests on nerves in my legs, placing a pair if needles each side of a
motor nerve, at each end of the nerve, and pulsing the nerve from a
signal generator. The sig gen fired a CRO with a camera and 100' roll
film back. They took thousands of pics over the couple of weeks,
measuring attenuation and velocity of propagation.

Yes, I am aware that there are parallels.

Owen

Barry,

I see I got the spelling of myelin wrong.

I remember things I see, and at that time I couldn't focus on things, never
saw the word written, was paralysed and was distressed at drowning in my
own secretions because I couldn't swallow and couldn't cough.

Anyway, I have got it now, myelin!

Owen

"Owen Duffy" wrote in message
...
Barry,

I see I got the spelling of myelin wrong.

Don't worry, Owen. Most of the time, I put two "l's" in the word
myself!

I remember things I see, and at that time I couldn't focus on
things, never saw the word written, was paralyzed and was
distressed at drowning in my own secretions because I couldn't
swallow and couldn't cough.

About two years ago I developed phlebitis. I went to the doctor
who had Doppler ultrasound tests run. He told me that my
circulation was good and that the swelling in the left leg would
clear up by itself within a week. But one of my toes swelled up and
cracked open. Being a diabetic, I immediately returned to the
physician. He told me that I had just enough time to drop by my
home and pick up some clean underwear to take with me to the
hospital. When I got to the emergency room, admission papers were
waiting. I had no idea that septicemia could set in so fast.

They amputated two toes, then another, and finally my entire left
foot. Meanwhile I had continuous IV injections of some of the
world's strongest antibiotics. I lost weight too - from 215 to 155
pounds. Small clumps of dead blood cells were sloughing off my
heart valves and one blocked a tiny capillary in my brain causing
expressive aphasia. It only lasted about three days, but I will
forever empathize with stroke victims. I could do complex math in
my head, but I could not speak a complete sentence. Fortunately I
started recovering soon after the foot was taken.

I am posting this history here as a warning to other diabetics. My
HgA1c had been running less than 5.5; most diabetics are considered
to have good control if this number is below 7. My point is that
even with good glucose control, problems can still develop.

I too have had nerve conduction studies. As you said, they stick
little electrodes in your muscles and nerve bundles, only now they have
fancy microprocessor-controlled machines to do the tests. But the tests
are just as painful!

The worst thing I remember was the neurologist bragging to his
nurse, telling her,"Now if I turn this knob, I can make his big toe
rotate counter-clockwise."

Thanks for an interesting discussion, Owen.

--
73, Dr. Barry L. Ornitz WA4VZQ

Dr. Barry L. Ornitz wrote:
I too have had nerve conduction studies.

I also. The voltage getting to the nerves in my
feet is 2% of normal.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

Cecil Moore wrote:
Dr. Barry L. Ornitz wrote:
I too have had nerve conduction studies.

I also. The voltage getting to the nerves in my
feet is 2% of normal.

That's because you're longer than anyone else.
73,
Tom Donaly, KA6RUH

Tom Donaly wrote:
That's because you're longer than anyone else.

Well, just longer than most. The doctor says that
when the distance from my spinal column to the
numbness in my legs gets equal to the distance
from my spinal column to my fingers, they will
also start to get numb. It's something that
happens but nobody seems to know why.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com