PG1995
Active Member
Hi
Q1: A copper wire is said to have the bandwidth of 1 MHz. I don't think it conveys the full information about bandwidth supported by a copper wire because bandwidth is highest frequency minus lowest frequency, therefore 1 MHz could be 13MHz-12MHz or it could be 21MHz-20MHz, etc. Do you see where I'm getting confused? Please help me. Thanks.
Q2: Previously, I used to think that a copper wire and a telephone wire are the same. But now I believe I was wrong because it is said that a telephone copper wire has bandwidth of 4 kHz which is enough to carry voice signals. Was I really having it all wrong? What does the term 'copper wire' exactly refer to?
Q3: In this thread you (assuming steveB is reading this) were telling me that a copper wire cannot support high frequencies because at high frequencies a copper wire is more like an antenna and moreover the resistive losses become too much. It looks like it all has to do with the skin effect. I hope I have it right. At high frequencies, the effective cross section will decrease to value that overall resistance becomes quite large and it explains the reason for increased resistive losses at high frequencies. But how a copper wire become a good antenna at high frequencies. I understand that at high frequencies most of current is pretty much flowing at the surface, but how does this phenomenon of current flowing at the surface boundary helps the wire to become a good antenna?
This is the reason which comes to my mind. An accelerating charge radiates energy in form of electromagnetic waves. Electric current is made up of many charges. As the frequency is increased, it means more cycles and hence more acceleration which results in more radiation and this makes it an antenna. Even at low frequency, there is an electromagnetic radiation but as, at low frequency, not much of the current is flowing around the outer edge therefore most of emitted radiation gets re-absorbed into the surrounding atoms. But at high frequency, most of the current flows near the outer edge therefore almost all the radiation goes into surrounding area and very little is re-absorbed. Thank you.
Regards
PG
Helpful Links:
1: https://www.electro-tech-online.com/mathematics-physics/135665-bandwidth-etc.html
2: https://www.electro-tech-online.com/threads/multiplexing-channel-etc.135748/
3: https://en.wikipedia.org/wiki/Skin_effect
4: **broken link removed**
5: https://whatis.techtarget.com/definition/skin-effect
6: https://docs.google.com/file/d/0B_XrsbDdR9NEZEZRRm9GZEwycWc/edit?usp=sharing (formulas for calculating power radiated by accelerating charge)
7: https://en.wikipedia.org/wiki/Larmor_formula
Q1: A copper wire is said to have the bandwidth of 1 MHz. I don't think it conveys the full information about bandwidth supported by a copper wire because bandwidth is highest frequency minus lowest frequency, therefore 1 MHz could be 13MHz-12MHz or it could be 21MHz-20MHz, etc. Do you see where I'm getting confused? Please help me. Thanks.
Q2: Previously, I used to think that a copper wire and a telephone wire are the same. But now I believe I was wrong because it is said that a telephone copper wire has bandwidth of 4 kHz which is enough to carry voice signals. Was I really having it all wrong? What does the term 'copper wire' exactly refer to?
Q3: In this thread you (assuming steveB is reading this) were telling me that a copper wire cannot support high frequencies because at high frequencies a copper wire is more like an antenna and moreover the resistive losses become too much. It looks like it all has to do with the skin effect. I hope I have it right. At high frequencies, the effective cross section will decrease to value that overall resistance becomes quite large and it explains the reason for increased resistive losses at high frequencies. But how a copper wire become a good antenna at high frequencies. I understand that at high frequencies most of current is pretty much flowing at the surface, but how does this phenomenon of current flowing at the surface boundary helps the wire to become a good antenna?
This is the reason which comes to my mind. An accelerating charge radiates energy in form of electromagnetic waves. Electric current is made up of many charges. As the frequency is increased, it means more cycles and hence more acceleration which results in more radiation and this makes it an antenna. Even at low frequency, there is an electromagnetic radiation but as, at low frequency, not much of the current is flowing around the outer edge therefore most of emitted radiation gets re-absorbed into the surrounding atoms. But at high frequency, most of the current flows near the outer edge therefore almost all the radiation goes into surrounding area and very little is re-absorbed. Thank you.
Regards
PG
Helpful Links:
1: https://www.electro-tech-online.com/mathematics-physics/135665-bandwidth-etc.html
2: https://www.electro-tech-online.com/threads/multiplexing-channel-etc.135748/
3: https://en.wikipedia.org/wiki/Skin_effect
4: **broken link removed**
5: https://whatis.techtarget.com/definition/skin-effect
6: https://docs.google.com/file/d/0B_XrsbDdR9NEZEZRRm9GZEwycWc/edit?usp=sharing (formulas for calculating power radiated by accelerating charge)
7: https://en.wikipedia.org/wiki/Larmor_formula
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