RG 11 cable for internet?

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zbang said:
It will not transmit "more data". It will however carry the given signal with lower losses. At 700Hz, generic RG6 loses about 5.6 dB/100 ft while RG11 is more like 4.7 dB. It adds up.

(Also, it doesn't require special connectors, it requires specific ones for that size and impedance, just like almost all coax.)
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To the extent that it lets you use a higher upper limit frequency because of its lower attenuation at that frequency the lower loss cable could give you more data bandwidth. But only if the transmission system can make use of that higher end.
And if the system is marginal because of a high error rate resulting from the attenuation, then you could get a higher net throughput from the better cable.
But improvement certainly is neither assured nor automatic.
 
GoldDigger said:
Basically it is a function of the relationship between the per length capacitance and per length inductance. It has no DC component. You change the characteristic impedance by changing the size of the center conductor (inductance) and/or the distance and dielectric between center and outer (capacitance).

The reason that it matters is that if you have a long transmission line and terminate it with a resistor whose value is the characteristic impedance there will be no reflection. If the termination is a higher resistance there will be a reflection that is in phase with the incoming signal. If it ls less than the characteristic impedance then there will be a reflection that is opposite in phase to the incoming signal.
With either an open circuit or a short circuit the amplitude of the reflection will be the same as the amplitude of the incoming signal.
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I get that; I studied transmission lines in school, back when dinosaurs walked the earth. What I am looking for is a definition of what it is and where the 75 ohm number (or whatever) is measured or derived. I guess I've just been lazy; Hi ho Google, awaaaaaaay! :D
 
ggunn said:
I get that; I studied transmission lines in school, back when dinosaurs walked the earth. What I am looking for is a definition of what it is and where the 75 ohm number (or whatever) is measured or derived. I guess I've just been lazy; Hi ho Google, awaaaaaaay! :D
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See post # 18.
It is the ratio of the applied voltage to the resulting current when a waveform is applied to the open end of an infinite transmission line.
The number 75 ohms comes naturally into radio use because it is the characteristic radiation impedance of a 1/4 wave half dipole (1/4 wave antenna whose input end is placed on an infinite ground plane).
Similarly a (total length) 1/2 wave balanced dipole has a characteristic impedance of 300 ohms, hence the use of 300 ohm twin lead as the standard.
Put in a balun with a 2:1 turn ratio and you convert between 300 ohm balanced and 75 ohm unbalanced.

Not quite sure when and why the other impedances (50 and 90 ohm) came into use, but 50 became the standard for direct digital data and Ethernet signaling, as well as for analog signals in scientific instruments.
 
zbang said:
To further muddy the waters, IBM "3270" terminals used RG62, which is 93 ohm (sometimes stated as 92). Don't ask me why, I'm too lazy right now to find out.
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At a quick guess, the use of higher ohm terminating resistors wasted less power for the same voltage level signals.
 
zbang said:
True, but the extra power might be less than half a watt. My suspicion is that it was IBM wanting to be different. That or they'd gotten a good deal on lots of RG62.
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Not much difference in terms of energy costs, but a lot in terms of the semiconductor drivers of that time, especially if trying to fit multiples into an IC.
Now as far as just wanting to be different, you just have to look at their twinax cable!
 
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