txlines (2023 Update)

What if ur brain is a lossy transmission line

What if you posted something intelligent about electronic design?

The brain conducts! I know an elderly person who had ECT for psychosis one time, it was miraculous.

Skin effect doesn't model well as a lossy transmission line.

For a modestly long line, one can measure its actual step response and come up with an LT Spice ltline model that is usefully close. I think there are more sophisticated models that include skin effect.

...

Do you mind showing your test setup to get that trace? You must have a back-emf diode on the coil, but that diminishing slope looks wrong...

What exactly are you doing to that poor coil?

John :-#)#

The setup is in the picture. The inductor goes between an SMA connector and ground. The scope trace is 50 ohm TDR.

Closeup:

Given a voltage step from a 50 ohm source, one would expect an inductor to have a spike of the applied step voltage, and an exponential decay towards ground with time constant L/50. What's cool is the initial flat, with the winding acting like a transmission line roughly 800 ps round-trip.

I think.

If I remember correctly at one time before it was known whether fiber optics would be feasible, the telcos were going to use helix microwave wave-guides for "broadband" data transmission

There were trials done using light, in a pipe guided by thermal gradients.

I remember when hills had giant sugar-scoop microwave antennas. Now they have cell towers. If we get gen5 or 6 cellular, all that will be gone.

Used to be a hill near me with some of that stuff on it as my father told it, all ripped down before my time I guess, but there are still a few former sites standing in New England I think, probably used for cell service now.

With respect to the circuit the back-EMF can't show up until it "knows" it's a finite inductor and not some fashion of infinite helical transmission line, 400 ps is ~4.7 inches at the speed of light, how long would the helix be if you stretched it out

We still have scoops on our telco (Telus) building here in Vancouver at Boundary and Kingsway. There is an obvious missing connection to the building from the bottom of each scoop:

John :-#)#

That inductor is 15 turns of about 0.1" diameter, so the wire length is about 4.7".

Good grief, right on! Of course, the dielectric is plastic, so the prop velocity is less than c. And there is coupling between the loops.

Yeah, it doesn't realize that it's actually a solenoid inductor until the incident wave makes the round trip. Sort of.

Some guys at Bell Labs discovered the universe's background radiation with a big scoop antenna. The initial noise figure was unaccountably high until they evicted some pigeons from inside.

and everything that conducts is an antenna.

A tree, for example. Ask any foxhunter what happens to signals in a forest, depending on the wavelength in use and the relative size of the branches and leaves. 70cm in a pine forest is a real doozy - the signal just vanishes.

New definitions:

• a conductor is a transmission line to the extent that it constrains the energy to follow it, rather than radiating it

• a conductor is an antenna to the extent that it radiates the energy delivered into it

These are complementary. Any conductor is both, in varying degree

CH

It wasn't so much the pigeons as their droppings. Rather like some of the posters here.

microwave links for long distance phone service is dead, but there's still a niche use for even longwave communications links across the US and the atlantic. Radiowaves are faster than light through fiber optics and in the world of high speed trading, faster wins.

Folks have already figured out that trees communicate through their roots and the fungi in the soil...

now perhaps they should see if they use radio waves? Super long wave, much likes subs use... Interesting fantasy, and may be something in it too.

The more we learn the more there is to learn! How anyone can say life is boring is beyond me.

John :-#)#

Long ago I remember seeing an Indian report that they could make a cheap antenna for the first TVs there. All they did was insert the coax signal line into a coconut tree near ground level.

. . . and Ground is everywhere.

RL