Timeline for How are unbalanced coaxial cables used for broadcasting TV signals without any problems?
Current License: CC BY-SA 4.0
12 events
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| Dec 17, 2019 at 10:26 | comment | added | Andy aka | Coax cable relies on the magnetic interference inducing opposing currents in the shield that cancel out the magnetic field inside. I don't think that sentence is right at all.(2nd paragraph in your answer @BruceAbbott) | |
| Sep 24, 2019 at 4:05 | history | bounty ended | CommunityBot | ||
| Sep 22, 2019 at 7:27 | comment | added | user173292 | That picture is tragic, fun, insane and impressive at the same time. Props for the picture, it speaks more than 1800 words (; | |
| Sep 17, 2019 at 23:06 | comment | added | Bruce Abbott | @DaveTweed Perhaps skin effect is not the best phrase since it is normally used to explain increased resistance at higher frequencies. It is what I was taught, but that was 40 years ago. Your link to the paper "magnetic field due to a coax cable" is broken, and I have not managed to find another that is satisfactory. Do you have one? | |
| Sep 17, 2019 at 20:05 | comment | added | Dave Tweed | Actually, that's wrong anyway. The phenomenon of skin depth has nothing whatsoever to do with coax's immunity to magnetic coupling -- in fact, that immunity relies on the fact that magnetic fields affect the inner and outer conductors equally. Additional details here. | |
| Sep 16, 2019 at 12:20 | history | edited | Bruce Abbott | CC BY-SA 4.0 |
added 218 characters in body
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| Sep 16, 2019 at 12:01 | comment | added | Bruce Abbott | The lower immunity is due to the larger penetration of the magnetic field into the cable because the 'skin effect' is less. I actually had that in my answer but took it out for brevity! | |
| Sep 16, 2019 at 11:26 | comment | added | user1245 | I was mostly asking why coax is less immune to low freq. interface than high freq. interface. I still dont understand many things here. | |
| Sep 16, 2019 at 10:47 | comment | added | Bruce Abbott | Magnetic interference induces a relatively low voltage in the wire. At lower impedance this voltage causes greater current flow and more noise power. A low impedance signal has lower voltage at a given power level so the noise to signal ratio is higher. eg. a 50 Ohm (low impedance) mic vs a 5k Ohm (high impedance) mic. Both mic cables get the same hum voltage induced in them, but the 5k mic is producing 10 times higher signal voltage at the same sound level so the hum is ten times less (-20dB) relative to the signal. | |
| Sep 16, 2019 at 10:09 | comment | added | user1245 | 2-) You then mentioned: "However the circuit impedances are generally in the 1k to 1M range so magnetic interference (which generates high current but low voltage) is less of an issue" I dont get this either. Can you also show this with a circuit model or an analogy ect? | |
| Sep 16, 2019 at 10:08 | comment | added | user1245 | I would like to ask couple of things bothers me since I dont understand those parts. 1-) You mentioned: "Coax cables are commonly used in audio to connect between components and inside equipment, despite not being very effective against low frequency magnetic interference." How can we show that from circuit model point of view that low frequency magnetic interference is the downside of the coax? Why a coax is less immune to low freq. interference? How to demonstrate this ? | |
| Sep 16, 2019 at 9:51 | history | answered | Bruce Abbott | CC BY-SA 4.0 |