Um, wrong. "Drool" is the technical term.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Actually, I may have seen coax drool. I once installed a ham radio repeater using Helix, which has a mostly air dielectric. That allows it to act as water plumbing. Upon arriving at the repeater site, after a few days of rain, I unscrewed the coax connector at the repeater end, only to find copious quantities of watery green "drool" pouring out of the coax cable. Someone forgot to embalm the antenna connector in PTFE tape and Scotch 66 to make it waterproof. So, yes, there is such a thing as coax drool.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Um, coming out the bottom, it's not "drool".
If Google can't find it, it doesn't exist. (Just ask the Chinese censors how that works).
Since there seems to be a vacancy in the technobabble jargon dictionary for an appropriate term, and I consider "drool" to be inadequately descriptive, may I suggest that a proper term should be the opposite of "ringing" as in "overdamped" which I'm borrowing from the medical profession:
Well, I'll be Damped - How Square Wave Testing Can Assure Accuracy in Your Hemodynamic Monitoring Interpretations
Basically, it's when a waveform tries to produce peaked waveform similar to ringing, but fails to rise to the occasion producing only a modest increase without any overshoot or peak.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
True. However, I don't believe that "coax diarrhea" would make a suitable substitute. See my comments on "underdamped" leading edge elsewhere in this rapidly deteriorating discussion.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Oops. My faulty memory and misreading the above web page. It's for the U800 horizontal hybrid. Thanks for the correction.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Coax stool?
And magnetic coupling to the next turn, yes.
Dispersion can go any way, it's a function of frequency. A resonant tank is dispersive in a very frequency-selective way. Arrays of them in space, make metamaterials with bizarre indices of refraction, over fairly narrow frequency ranges. (Analogously, you could make a lumped equivalent transmission line from coupled resonators; this is actually of practical use, in distributed amplifiers on the bleeding edge of bandwidth capability, like those 200GHz chips they're playing with.)
Gradual, lossy dispersion, is manifested -- as others have been discussing -- with coax and such. The wave velocity isn't much different (with respect to frequency), nor is the amplitude really, but in typical applications, the latter is much more important than the former.
The velocity is actually different, but by little enough that you don't notice, and because it's a smooth smearing-out over all frequencies, it doesn't manifest as ringing or echoes or anything, it just looks like a rounding-off. Instead of a sharp edge or spike, you get a softer edge (plus drool), or hump.
The fact that it's lossy, is a direct consequence of the slight change in velocity. Complex numbers and all that. Or if the velocity changes rapidly, so does the amplitude (in a complementary way). Resonant tanks are frequency-selective (an amplitude effect), and have a ton of group delay around the center frequency.
The helical TL tends to exhibit a ringing behavior, where the high frequencies arrive a little before, I think? A bit like Gibb's phenomenon, but corresponding to the bandwidth and dispersion of the medium, rather than stacking up harmonics of course.
Tim
-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Design Website: https://www.seventransistorlabs.com/
Does it have to be coax? It might be easier to do it with a spiral wound spring steel wire and impulse actuators and microphones. A variant of that sort of delay line was use for some early computer memory.
Although you might want to use compressive excitation to maximise the dispersion rather than torsional. It should be a lot easier to see something at the speed of sound with fairly ordinary lab gear.
-- Regards, Martin Brown
Hey thanks everyone... Jeff, Tim, Martin. I'm posting a link to the discussion with the physics lab guy group.
George H.
to you.
ery long coax cable and look at the output of the cable with an oscilloscop e to see that the high frequencies are traveling faster than the low freque ncies. Anyone in Tapper land do an experiment like this or a similar varia tion?
t I wondered if there was some other transmission line
The Lower frequencies of light waves travel faster than higher frequencies of light waves in space. Yes? Am I correct?
The Shive wave machine can be used to show this. The Shive machine with the long rods has a shorter wavelength and a slower velocity. The Shive machine with the shorter rods has a longer wavelength and a highe r velocity.
The book by J. N. Shive called "Similarities in wave behavior", Bell Teleph one Laboratories (1973) has this topic, if I am correct.
A Cosmology Faculty and I had discussed this just yesterday.
- Jerry
funny you should ask about this,
I just "read" this article
see the section # 7 about the sounds of the long steel cables in Northern Italy.
You can hear the dispersion very easily, a transient from a hit with a stick is spread into a chirp.
Mark
n to you.
very long coax cable and look at the output of the cable with an oscillosc ope to see that the high frequencies are traveling faster than the low freq uencies. Anyone in Tapper land do an experiment like this or a similar var iation?
But I wondered if there was some other transmission line
s of light waves in space.
Hi Jerry, Well in vacuum all the same velocity. But in glass I think that's right. The Feynman lectures has a nice semi-classical discussion of dispersion in glass, where there is some high frequency resonance (higher than the light frequencies.) And this gives more (phase shift?*) and slower velocity to the blue light... that is closer to the resonance.
George H.
*I'm very much afraid, I'm using the wrong term/word and will need to go re-read.r velocity.
her velocity.
phone Laboratories (1973) has this topic, if I am correct.
Right. Just on the other side of the resonance is the 'anomalous dispersion' region, where n drops with f.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
It can be cool to listen to things that aren't natively audible. Heterodyned ultrasonics, AC magnetic fields, VLF atmospherics and e-fields, vibrations, earth potentials, highpass filtered AC power lines, raindrop and snow electric effects, insect electric effects.
Photodetectors aimed at things. Cars with modern lighting and lidar should be fun. Also HF flourescent/LED lighting, LED billboards, lightning, freeway illumination. Fans.
Car tire electric fields? Running shoes?
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Yup, steel wire is dispersive, because the stiffness of the wire has more effect at high frequency. So a music-wire spring might make a good dispersion demo.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
People have measured fast events that have traveled for millions of light-years through space, and everything, including gravity, seems to have the same velocity.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
I made a fun little audio-frequency magnetic probe last year, using a salvaged wire coil (used to be the drive element in a big reed relay) and a dual NPN transistor as a long-tailed-pair differential amp. It plugs into an Android phone/tablet's headset jack.
Seeing all of the AC- and switching-noise hash in the 20-20kHz range, on a little audio-spectrum-analyzer app, is quite interesting.
In fact, the only related thing they've measured as noticeably slower, is radio waves. Well, guess what, there's a lot of ionized and polarizable particles between here and there, giving a slight index of refraction at low frequencies, which is mostly skimmed past by gravity and gammas.
The thought occurred to me recently, we might set up long wave antennas -- they'd have to be arrays in space, because of the length -- to hunt for alien power signatures. Because, hey, their mains systems aren't likely to fall outside the 20-200Hz range we settled on! Then I immediately recalled... oh, yeah, the solar system's own conductivity alone probably shields that (and swamps with noise), very effectively. And interstellar space (should we be so excited as to make such distant probes for this) isn't much better (especially considering the distance). Right... ;-)
Speaking of antennas, those aren't very necessary anyway, thanks to the nT and even pT resolution we have on magnetometers. Voyager is already listening to the Sun, and now galaxy, out there, no enormous elements needed. Yay!
Tim
-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Design Website: https://www.seventransistorlabs.com/
on to you.
a very long coax cable and look at the output of the cable with an oscillos cope to see that the high frequencies are traveling faster than the low fre quencies. Anyone in Tapper land do an experiment like this or a similar va riation?
But I wondered if there was some other transmission line
es of light waves in space.
Actually billions of light-years - though you mostly need a gravitational l ens somewhere along the way to give you enough light.
was only 130 million light years away, but we did get it all at once.
-- Bill Sloman, Sydney
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