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Author Topic: Velocity Factor  (Read 5234 times)
N4CR
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« Reply #15 on: May 29, 2012, 04:25:29 PM »

Seldom do new discoveries negate previous understandings.

The future will hold deeper understanding of reality but it won't be wildly different than what we understand now. Just more refined.
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73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
W0BTU
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« Reply #16 on: May 29, 2012, 05:53:27 PM »

I have to tip my hat to you guys who know far more than I could ever imagine. ... I wonder if in a century (or less) scientists will have a different view of reality than we currently hold.

Well said! :-)

I admire physicists who study this sort of thing, and this subject fascinates me. But if we think that physicists have it all figured out and there are no more profound discoveries to make, we're kidding ourselves.

Michelson and Morely demonstrated that there was not an ether (aether). But no less a genius than Prof. Richard Feynman himself disagreed with the notion that a vacuum was totally empty. https://en.wikipedia.org/wiki/Quantum_vacuum
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K4RVN
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« Reply #17 on: May 29, 2012, 07:15:58 PM »

Don,
Don't feel alone, I could not find celearus in any dictionary including the Oxford Advanced Learners Dictionary. It must be so old it is forgotten now. However celer appears in many of our English words like accelerate and in the dictionaries.

Frank
« Last Edit: May 29, 2012, 08:35:07 PM by K4RVN » Logged
W5DXP
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« Reply #18 on: May 30, 2012, 05:10:47 AM »

I too, as a layman, thought that photons were bits of light, so my education has been extended.

A physicist will tell you that photons are indeed bits of light whose frequencies extend from almost DC to almost infinity which includes RF, i.e. anything involving photons is considered "light" by physicists. Some is visible light and some is not visible. One of my physics textbooks on EM waves was simply titled, Light.

The background radiation in the universe was once visible light but now, those same photons are in the RF microwave frequency range.
« Last Edit: May 30, 2012, 05:50:05 AM by W5DXP » Logged

73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
W5DXP
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« Reply #19 on: May 30, 2012, 05:31:42 AM »

The photon nature of EM waves is pretty irrelevant to radio communications ...

There is one thing that makes photons very relevant to radio communications - it is impossible for EM waves to do anything that photons cannot do, i.e. it is impossible for EM waves to violate the known laws of physics regarding photons. For instance:

Photons cannot stand still and must necessarily move at the speed of light in the medium while transporting energy and momentum. Therefore, EM waves cannot stand still, i.e. RF "standing waves" are not standing still and do not even meet the definition of "EM wave". Their component forward and reverse traveling waves are always moving at the speed of light in the medium. Here's what Eugene Hecht, author of Optics, said about "standing waves".

"These ... patterns are called standing waves, as compared to the propagating waves considered above. They might better not be called waves at all, since they do not transport energy and momentum."

One will hear certain ham gurus proclaiming that reflected waves cease to exist during steady state conditions. That is simply an illusion. Quoting "Electrical Communication", by Albert: "Such a plot of voltage is usually referred to as a voltage standing wave or as a stationary wave. Neither of these terms is particularly descriptive of the phenomenon. A plot of effective values of (standing wave) voltage, appearing as in Fig. 6(e), is not a wave in the usual sense. However, the term "standing wave" is in widespread use."

« Last Edit: May 30, 2012, 05:42:02 AM by W5DXP » Logged

73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
STAYVERTICAL
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Posts: 854




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« Reply #20 on: May 30, 2012, 01:13:00 PM »

Thanks Cecil,

As I sit here I have a fan going on a table.
Looking at my cup of coffee, I see the vibration of the fan has produced what I presume are standing waves.
There are a lot of concentric waves standing still on the surface of the coffee, and I guess these are formed
from the interaction between forward and reflected waves in the liquid.

So, like EM waves on a feedline, I guess my cup of coffee now has an SWR which I could measure by taking
the ratio of the maximum wave height to the minimum wave height.
It may even be possible to measure the frequency of the vibration by measuring the distance between crests.
This is similar to the old old "Lecher line" method of measuring frequency on open wire feedlines.

Amongst it's other benefits, it looks like coffee can now solve SWR problems. Smiley

Thanks for the info Cecil, very interesting.

73 - Rob
« Last Edit: May 30, 2012, 01:39:09 PM by STAYVERTICAL » Logged
W0BTU
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« Reply #21 on: May 30, 2012, 02:15:28 PM »

If standing waves in your coffee interests you, you'll love this fascinating Bell Labs video about the Shive mechanical wave machine. It beautifully demonstrates wave motion, SWR, and matching sections on a completely mechanical tabletop device.
http://techchannel.att.com/play-video.cfm/2011/3/7/AT&T-Archives-Similarities-of-Wave-Behavior

I suppose if he would have submerged that thing in a liquid, then Dr. Shive also could have demonstrated velocity factor.  Grin
« Last Edit: May 30, 2012, 02:17:16 PM by W0BTU » Logged

STAYVERTICAL
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Posts: 854




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« Reply #22 on: May 30, 2012, 02:50:32 PM »

If standing waves in your coffee interests you, you'll love this fascinating Bell Labs video about the Shive mechanical wave machine. It beautifully demonstrates wave motion, SWR, and matching sections on a completely mechanical tabletop device.
http://techchannel.att.com/play-video.cfm/2011/3/7/AT&T-Archives-Similarities-of-Wave-Behavior

I suppose if he would have submerged that thing in a liquid, then Dr. Shive also could have demonstrated velocity factor.  Grin

Great video Mike,

In 28 minutes Dr. Shive explains just about everything about transmission lines and much more.
If every new ham was to watch this, the forums would be nearly devoid of questions on SWR and feedlines.

I love the 1950's style of explaining science - it is both human, innocent and excited in delivery.

This lecturer/engineer seems like a big kid to me - and I mean that in the most complimentary way possible.
A guy who seems like both a nice person and someone who has not lost the thrill of scientific exploration.

Thank you Mike, for a link to a fascinating video.

73 - Rob

« Last Edit: May 30, 2012, 02:54:54 PM by STAYVERTICAL » Logged
K4JSR
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Posts: 513




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« Reply #23 on: May 31, 2012, 01:04:30 AM »

Cecil asked, "I wonder if Einstein, while riding the crest of the EM wave, could detect a change in momentum?"

He could not because he was crestfallen!   Undecided

73,  Cal  K4JSR
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KC9TNH
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Posts: 304




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« Reply #24 on: May 31, 2012, 05:56:39 AM »

Is it that electromagnetic energy travels more slowly...
or....
Invoking anthropomorhism, AE4RV once told me simply:

"Electroncs are lazy."

At a practical level that has worked many times for me.
(I am gonna check out that video 'cause I'm still a 60yo kid.)
 Grin
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73
Wes -KC9TNH
"Don't get treed by a chihuahua." - Pete
KG6AF
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Posts: 332




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« Reply #25 on: May 31, 2012, 08:34:17 AM »

I love the 1950's style of explaining science - it is both human, innocent and excited in delivery.

It didn't start in the 1950's: you can find similar examples from earlier decades.  The industrial films of the 30's  and 40's often conveyed complex ideas in very imaginative ways.  In particular, an outfit called the Jam Handy Organization made great films.  For example, if you ever wanted to learn how an car's differential worked, you'd have a hard time doing better than watching this film:

http://archive.org/details/Aroundth1937
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STAYVERTICAL
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Posts: 854




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« Reply #26 on: May 31, 2012, 06:28:50 PM »

I love the 1950's style of explaining science - it is both human, innocent and excited in delivery.

It didn't start in the 1950's: you can find similar examples from earlier decades.  The industrial films of the 30's  and 40's often conveyed complex ideas in very imaginative ways.  In particular, an outfit called the Jam Handy Organization made great films.  For example, if you ever wanted to learn how an car's differential worked, you'd have a hard time doing better than watching this film:

http://archive.org/details/Aroundth1937

I agree - they did not have the sophisticated computer animation possible today, but in both instructional video and movies they knew how to get the message across.
Even the old "Watch mr wizard" episodes were great to teach kids science.
I particularly remember watching one about how loudspeakers work, by putting some sand in a speaker cone, and connecting it to A.C.
I tried this but omitted the low voltage transformer (no instant replay in those days) - and duly blew the house fuses.

This and other shows like it, kick started my ham career (and many more blown fuses) - so it is sad that society has changed so
much today that shows like those are no longer mainstream.

Custom IC's and firmware are very predominant today, but the basics of electronics still rule.
Although it would not be as sophisticated, it is still possible to produce a radio transmitter and receiver with standard components.
So, knowing the fundamentals of electronics is still as valid today as it was in 1920.




 
« Last Edit: June 01, 2012, 12:44:51 AM by STAYVERTICAL » Logged
W0BTU
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« Reply #27 on: June 01, 2012, 03:37:48 PM »

... The industrial films of the 30's  and 40's often conveyed complex ideas in very imaginative ways.  In particular, an outfit called the Jam Handy Organization made great films.

Even the old "Watch mr wizard" episodes were great to teach kids science.


That brings back some nice memories. :-)  I loved Mr. Wizard (Bob Herbert) on TV when I was a kid. And I've seen Jam Handy films, probably at the vo-tech HS I graduated from in 1972.
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K7KBN
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Posts: 2753




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« Reply #28 on: June 01, 2012, 05:35:21 PM »

I watched Mr. Wizard when he was DON Herbert.
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73
Pat K7KBN
CWO4 USNR Ret.
W0BTU
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« Reply #29 on: June 01, 2012, 07:11:09 PM »

Yes, Don it was.

Hey, it's been 50 years since I even thought of him!  Grin
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