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Author Topic: 90 degree adapters lossy -- why?  (Read 1008 times)

Dave Garoutte

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Re: 90 degree adapters lossy -- why?
« Reply #10 on: September 11, 2018, 04:47:18 pm »

Technically at about 70% the speed of light  ;)
That would be the propagation velocity. 

Lee
I did say through copper.
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Lee Buckalew

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Re: 90 degree adapters lossy -- why?
« Reply #11 on: September 12, 2018, 03:08:42 pm »

I did say through copper.

Dave, I don't think that I am following you here.  Electricity does not travel at the speed of light through copper, it travels at approximately 70% of the speed of light.

Lee
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Dave Garoutte

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Re: 90 degree adapters lossy -- why?
« Reply #12 on: September 12, 2018, 03:22:20 pm »

Dave, I don't think that I am following you here.  Electricity does not travel at the speed of light through copper, it travels at approximately 70% of the speed of light.

Lee

The typical value for the speed of light (C) refers to its speed in a vacuum.
The medium through which it travels effects the actual speed.
The speed of light through glass is different than the speed of light through air, which is why lenses work.
If the medium is copper, it is .7C.
That is the speed of light through copper.
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Matthew Knischewsky

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Re: 90 degree adapters lossy -- why?
« Reply #13 on: September 12, 2018, 04:56:53 pm »

The typical value for the speed of light (C) refers to its speed in a vacuum.
The medium through which it travels effects the actual speed.
The speed of light through glass is different than the speed of light through air, which is why lenses work.
If the medium is copper, it is .7C.
That is the speed of light through copper.

But what if the copper is blocking the light?
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Len Zenith Jr

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Re: 90 degree adapters lossy -- why?
« Reply #14 on: September 12, 2018, 07:02:03 pm »

But what if the copper is blocking the light?

There is a lot more to the electromagnetic spectrum than visible light.
Copper only blocks light longer than 115 nm wavelegnth. Above that it is mostly transparent to light. X-rays mostly pass right through.
spectrum
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Scott Holtzman

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Re: 90 degree adapters lossy -- why?
« Reply #15 on: September 12, 2018, 08:45:54 pm »

The typical value for the speed of light (C) refers to its speed in a vacuum.
The medium through which it travels effects the actual speed.
The speed of light through glass is different than the speed of light through air, which is why lenses work.
If the medium is copper, it is .7C.
That is the speed of light through copper.

Isn't that what the velocity of propagation value indicates?
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Lee Buckalew

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Re: 90 degree adapters lossy -- why?
« Reply #16 on: September 13, 2018, 12:15:36 pm »

Isn't that what the velocity of propagation value indicates?

Yes, that is why I was not understanding. 
Also, the standard use of (c) as the constant for the speed of light is understood as the speed of light in a vacuum. 
It can sometimes be used as the speed of light in any medium while (c), with a subtext 0, is used to reference the speed of light in a vacuum.

Lee
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Jay Barracato

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Re: 90 degree adapters lossy -- why?
« Reply #17 on: September 13, 2018, 04:37:44 pm »

Yes, that is why I was not understanding. 
Also, the standard use of (c) as the constant for the speed of light is understood as the speed of light in a vacuum. 
It can sometimes be used as the speed of light in any medium while (c), with a subtext 0, is used to reference the speed of light in a vacuum.

Lee
Dave's original response did not refer to c, it referred to the speed of light in copper, which I clearly understood to be the speed of the wave in the medium.

The speed of the wave is simply the ratio of the wavelength and period, and in my mind does not really factor into the cause of reflections.

What happens when you put a sub playing a note with a 40 hz fundamental in a 25 ft room?

What happens when you put an offer signal with a wavelength of .7m to 7m on a cable whos length is similar to that length?

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Scott Helmke

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Re: 90 degree adapters lossy -- why?
« Reply #18 on: September 13, 2018, 04:41:50 pm »

What happens when you put a sub playing a note with a 40 hz fundamental in a 25 ft room?

What happens when a wave hits the wall of the pool?
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Jay Barracato

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Re: 90 degree adapters lossy -- why?
« Reply #19 on: September 13, 2018, 09:12:08 pm »

What happens when a wave hits the wall of the pool?
What I am getting at is this is NOT a case of simple reflection.

The oscillation carrying the RF signal is actually a longitudinal wave that is modulated on to the transverse waves of the electric and magnetic fields. The signal oscillation is fundamentally one dimensional. That is why is is perhaps easier to picture the signal as an oscillation in the voltage or current values rather than by a distribution of charge.

Now the key point, the superposition of the primary signal with it's reflection can mean the summation of a frequency with a slightly different frequency as the signal is modulated. This sets up another layer of modulation (called beats) that oscillates much slower than the original signal. This is actually the same thing you listen for when you tune one guitar strings against another.

In other words, weird things happen with reflections and superposition when the wavelength of oscillation is similar in size to the space in which the oscillation occurs.

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