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#81
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The decibel
"The Phantom" wrote in message ... On Tue, 21 Aug 2007 07:35:03 -0400, "Arny Krueger" wrote: "Eeyore" wrote in message ... Arny Krueger wrote: "Eeyore" wrote: John Byrns wrote: A Bel or 10 dB seems like an awfully large loss for "a standard telephone line over the distance of one mile, at 1kHz", is this really correct? I suggest you consider the DC resistance of a mile (and a mile back) of thin wire. Telephone wire in the US is usually 24 or 26 gauge. Taking the worst case: 26 gauge - 40 ohms/1000 feet = 211 ohms/mile, presuming the return path is a low resistance ground. The reurn is a length of the same wire. Yes, the line is usually balanced. So about double the loss to about 5 dB/mile. Presuming the load is 600 ohms, loss is 0.739 or 2.6 dB. The load is rarely 600 ohms AIUI. Do you think it is higher or lower than 600 ohms? An example is given on page 69 of the book "Transmission Circuits for Telephonic Communication". I quote: "In order to get a clearer idea of what is meant by transformer and transition losses as well as to get a more concrete idea of their order of magnitude, let us consider the case of an e.m.f. E acting through a sending end impedance Z1 of 240 - j123 ohms and connected to a receiving end impedance Z2 of 623 - j350 ohms." Make of it what you will. The magnitude of the source is 269 ohms. The magnitude of the load is 714 ohms On page 70 and 71, they discuss a test set for comparing transmitters (carbon microphones, I think). The circuit simulates the sending end circuitry of a telephone and has 8 miles of cable as well as some transformers and induction coils (as they called them; they were just inductors). The impedance driving the telephone line wasn't just the impedance of the microphone; it was modified by the additional circuitry. They then say: "In this particular circuit the 800 cycle impedance at the transmitter terminals is approximately 307 - j74 ohms. It is, therefore, seen that with present commercial types of transmitters, ranging between 30 and 150 ohms in resistance, this circuit will discriminate in favor of the transmitter having the higher resistance." ------------------------------------------------------------------------- The magnitude of the source is 315 ohms. On page 150, they say: "For example, the 800-cycle iterative impedance of a non-loaded No. 19 gauge cable circuit is approximately 500 @ 45 degrees, and that of a non-loaded open wire line is about 700 @ 14 degrees ohms." 500 ohms and 700 ohms are impedance magnitudes as is. Thanks. |
#82
Posted to rec.audio.tubes
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The decibel
In article ,
"Arny Krueger" wrote: "The Phantom" wrote in message ... On Tue, 21 Aug 2007 07:35:03 -0400, "Arny Krueger" wrote: "Eeyore" wrote in message ... Arny Krueger wrote: "Eeyore" wrote: John Byrns wrote: A Bel or 10 dB seems like an awfully large loss for "a standard telephone line over the distance of one mile, at 1kHz", is this really correct? I suggest you consider the DC resistance of a mile (and a mile back) of thin wire. Telephone wire in the US is usually 24 or 26 gauge. Taking the worst case: 26 gauge - 40 ohms/1000 feet = 211 ohms/mile, presuming the return path is a low resistance ground. The reurn is a length of the same wire. Yes, the line is usually balanced. So about double the loss to about 5 dB/mile. Presuming the load is 600 ohms, loss is 0.739 or 2.6 dB. The load is rarely 600 ohms AIUI. Do you think it is higher or lower than 600 ohms? An example is given on page 69 of the book "Transmission Circuits for Telephonic Communication". I quote: "In order to get a clearer idea of what is meant by transformer and transition losses as well as to get a more concrete idea of their order of magnitude, let us consider the case of an e.m.f. E acting through a sending end impedance Z1 of 240 - j123 ohms and connected to a receiving end impedance Z2 of 623 - j350 ohms." Make of it what you will. The magnitude of the source is 269 ohms. The magnitude of the load is 714 ohms On page 70 and 71, they discuss a test set for comparing transmitters (carbon microphones, I think). The circuit simulates the sending end circuitry of a telephone and has 8 miles of cable as well as some transformers and induction coils (as they called them; they were just inductors). The impedance driving the telephone line wasn't just the impedance of the microphone; it was modified by the additional circuitry. They then say: "In this particular circuit the 800 cycle impedance at the transmitter terminals is approximately 307 - j74 ohms. It is, therefore, seen that with present commercial types of transmitters, ranging between 30 and 150 ohms in resistance, this circuit will discriminate in favor of the transmitter having the higher resistance." ------------------------------------------------------------------------- The magnitude of the source is 315 ohms. On page 150, they say: "For example, the 800-cycle iterative impedance of a non-loaded No. 19 gauge cable circuit is approximately 500 @ 45 degrees, and that of a non-loaded open wire line is about 700 @ 14 degrees ohms." 500 ohms and 700 ohms are impedance magnitudes as is. Why do you focus on the magnitude of the impedance to the exclusion of the phase angle? According to the old telephone book I have the phase angle of the impedance is also important in telephonic transmission. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#83
Posted to rec.audio.tubes
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The decibel
"John Byrns" wrote in message ... In article , "Arny Krueger" wrote: "The Phantom" wrote in message ... On Tue, 21 Aug 2007 07:35:03 -0400, "Arny Krueger" wrote: "Eeyore" wrote in message ... Arny Krueger wrote: "Eeyore" wrote: John Byrns wrote: A Bel or 10 dB seems like an awfully large loss for "a standard telephone line over the distance of one mile, at 1kHz", is this really correct? I suggest you consider the DC resistance of a mile (and a mile back) of thin wire. Telephone wire in the US is usually 24 or 26 gauge. Taking the worst case: 26 gauge - 40 ohms/1000 feet = 211 ohms/mile, presuming the return path is a low resistance ground. The reurn is a length of the same wire. Yes, the line is usually balanced. So about double the loss to about 5 dB/mile. Presuming the load is 600 ohms, loss is 0.739 or 2.6 dB. The load is rarely 600 ohms AIUI. Do you think it is higher or lower than 600 ohms? An example is given on page 69 of the book "Transmission Circuits for Telephonic Communication". I quote: "In order to get a clearer idea of what is meant by transformer and transition losses as well as to get a more concrete idea of their order of magnitude, let us consider the case of an e.m.f. E acting through a sending end impedance Z1 of 240 - j123 ohms and connected to a receiving end impedance Z2 of 623 - j350 ohms." Make of it what you will. The magnitude of the source is 269 ohms. The magnitude of the load is 714 ohms On page 70 and 71, they discuss a test set for comparing transmitters (carbon microphones, I think). The circuit simulates the sending end circuitry of a telephone and has 8 miles of cable as well as some transformers and induction coils (as they called them; they were just inductors). The impedance driving the telephone line wasn't just the impedance of the microphone; it was modified by the additional circuitry. They then say: "In this particular circuit the 800 cycle impedance at the transmitter terminals is approximately 307 - j74 ohms. It is, therefore, seen that with present commercial types of transmitters, ranging between 30 and 150 ohms in resistance, this circuit will discriminate in favor of the transmitter having the higher resistance." ------------------------------------------------------------------------- The magnitude of the source is 315 ohms. On page 150, they say: "For example, the 800-cycle iterative impedance of a non-loaded No. 19 gauge cable circuit is approximately 500 @ 45 degrees, and that of a non-loaded open wire line is about 700 @ 14 degrees ohms." 500 ohms and 700 ohms are impedance magnitudes as is. Why do you focus on the magnitude of the impedance to the exclusion of the phase angle? According to the old telephone book I have the phase angle of the impedance is also important in telephonic transmission. Just trying to keep it simple. ;-) |
#84
Posted to rec.audio.tubes
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The decibel
Arny Krueger wrote: "Eeyore" wrote Arny Krueger wrote: "Eeyore" wrote: John Byrns wrote: A Bel or 10 dB seems like an awfully large loss for "a standard telephone line over the distance of one mile, at 1kHz", is this really correct? I suggest you consider the DC resistance of a mile (and a mile back) of thin wire. Telephone wire in the US is usually 24 or 26 gauge. Taking the worst case: 26 gauge - 40 ohms/1000 feet = 211 ohms/mile, presuming the return path is a low resistance ground. The reurn is a length of the same wire. Yes, the line is usually balanced. So about double the loss to about 5 dB/mile. Presuming the load is 600 ohms, loss is 0.739 or 2.6 dB. The load is rarely 600 ohms AIUI. Do you think it is higher or lower than 600 ohms? I was under the impression it could be lower but I see the standards still refer to 600 ohms. The characteristic impedance of the twisted pair cable is actually around 100 ohms and DSL circuits operate at this impedance. So it's 600 ohms for audio and 100 ohms for data. Graham |
#85
Posted to rec.audio.tubes
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The decibel
On Wed, 22 Aug 2007 03:15:13 +0100, Eeyore
wrote: Do you think it is higher or lower than 600 ohms? I was under the impression it could be lower but I see the standards still refer to 600 ohms. The characteristic impedance of the twisted pair cable is actually around 100 ohms and DSL circuits operate at this impedance. So it's 600 ohms for audio and 100 ohms for data. The big numbers are for open-wire line with huge (by modern standards) spacing. Modern plastic-insulated twisted pairs tend to fall, as you say, around 100 ohms. And the World is 72 ohms. The Wires have almost got it right. Thanks, as always, Chris Hornbeck "It's just this little Chromium Switch. You people are SO superstitious." |
#86
Posted to rec.audio.tubes
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The decibel
In article ,
Eeyore wrote: Arny Krueger wrote: "Eeyore" wrote Arny Krueger wrote: "Eeyore" wrote: John Byrns wrote: A Bel or 10 dB seems like an awfully large loss for "a standard telephone line over the distance of one mile, at 1kHz", is this really correct? I suggest you consider the DC resistance of a mile (and a mile back) of thin wire. Telephone wire in the US is usually 24 or 26 gauge. Taking the worst case: 26 gauge - 40 ohms/1000 feet = 211 ohms/mile, presuming the return path is a low resistance ground. The reurn is a length of the same wire. Yes, the line is usually balanced. So about double the loss to about 5 dB/mile. Presuming the load is 600 ohms, loss is 0.739 or 2.6 dB. The load is rarely 600 ohms AIUI. Do you think it is higher or lower than 600 ohms? I was under the impression it could be lower but I see the standards still refer to 600 ohms. The characteristic impedance of the twisted pair cable is actually around 100 ohms and DSL circuits operate at this impedance. So it's 600 ohms for audio and 100 ohms for data. I believe the problem here is that the characteristic impedance of this type of cable varies with frequency because it doesn't have enough inductance. The result is that the characteristic impedance is higher at voice frequencies than it is at ultrasonic frequencies. Back in the days when telephone loops were used in radio for remote broadcasts and linking the studio to the transmitter site, this effect was used to advantage to equalize short loops by terminating them in 150 Ohms rather than 600 Ohms. This optimized the transmission at the higher audio frequencies, where the losses were greater, relative to the lower frequencies, by mismatching the line at low frequencies while matching it properly at high frequencies. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#87
Posted to rec.audio.tubes
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The decibel
In article ,
Chris Hornbeck wrote: On Wed, 22 Aug 2007 03:15:13 +0100, Eeyore wrote: Do you think it is higher or lower than 600 ohms? I was under the impression it could be lower but I see the standards still refer to 600 ohms. The characteristic impedance of the twisted pair cable is actually around 100 ohms and DSL circuits operate at this impedance. So it's 600 ohms for audio and 100 ohms for data. The big numbers are for open-wire line with huge (by modern standards) spacing. Modern plastic-insulated twisted pairs tend to fall, as you say, around 100 ohms. While I believe the characteristic impedance of open wire lines is higher than that of cables, as you say, that is far from the entire story. The characteristic impedance of cable is greatly dependent on frequency as a result of not having the correct ratio of inductance to capacitance. The result is that the characteristic impedance of cable varies with frequency, being lower at ultrasonic frequencies than at lower audio frequencies. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#88
Posted to rec.audio.tubes
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The decibel
On Wed, 22 Aug 2007 15:58:52 GMT, John Byrns wrote:
In article , Chris Hornbeck wrote: On Wed, 22 Aug 2007 03:15:13 +0100, Eeyore wrote: Do you think it is higher or lower than 600 ohms? I was under the impression it could be lower but I see the standards still refer to 600 ohms. The characteristic impedance of the twisted pair cable is actually around 100 ohms and DSL circuits operate at this impedance. So it's 600 ohms for audio and 100 ohms for data. The big numbers are for open-wire line with huge (by modern standards) spacing. Modern plastic-insulated twisted pairs tend to fall, as you say, around 100 ohms. While I believe the characteristic impedance of open wire lines is higher than that of cables, as you say, that is far from the entire story. The characteristic impedance of cable is greatly dependent on frequency as a result of not having the correct ratio of inductance to capacitance. Once you're above the corner frequency, this is no longer true, until the frequency is very high. See: http://www.prc68.com/I/Zo.shtml It's the open wire lines that have the 600 ohm impedance. That is what they were using in the early days of telephone, and we inherited that 600 ohm legacy for telephone equipment for many years. The example of an open wire line given on the web page referenced is of a pair of 6 gauge (!!) wires, 1 foot apart. The result is that the characteristic impedance of cable varies with frequency, being lower at ultrasonic frequencies than at lower audio frequencies. Regards, John Byrns |
#89
Posted to rec.audio.tubes
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The decibel
John Byrns wrote: Eeyore wrote: Arny Krueger wrote: "Eeyore" wrote Arny Krueger wrote: "Eeyore" wrote: John Byrns wrote: A Bel or 10 dB seems like an awfully large loss for "a standard telephone line over the distance of one mile, at 1kHz", is this really correct? I suggest you consider the DC resistance of a mile (and a mile back) of thin wire. Telephone wire in the US is usually 24 or 26 gauge. Taking the worst case: 26 gauge - 40 ohms/1000 feet = 211 ohms/mile, presuming the return path is a low resistance ground. The reurn is a length of the same wire. Yes, the line is usually balanced. So about double the loss to about 5 dB/mile. Presuming the load is 600 ohms, loss is 0.739 or 2.6 dB. The load is rarely 600 ohms AIUI. Do you think it is higher or lower than 600 ohms? I was under the impression it could be lower but I see the standards still refer to 600 ohms. The characteristic impedance of the twisted pair cable is actually around 100 ohms and DSL circuits operate at this impedance. So it's 600 ohms for audio and 100 ohms for data. I believe the problem here is that the characteristic impedance of this type of cable varies with frequency because it doesn't have enough inductance. The same must be true of Cat5 etc in that case. In nay case, the charcteristic impedance is AIUI simply determined by the physical properties of the line (conductor dia and spacing notably). Graham |
#90
Posted to rec.audio.tubes
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The decibel
In article ,
The Phantom wrote: On Wed, 22 Aug 2007 15:58:52 GMT, John Byrns wrote: In article , Chris Hornbeck wrote: On Wed, 22 Aug 2007 03:15:13 +0100, Eeyore wrote: Do you think it is higher or lower than 600 ohms? I was under the impression it could be lower but I see the standards still refer to 600 ohms. The characteristic impedance of the twisted pair cable is actually around 100 ohms and DSL circuits operate at this impedance. So it's 600 ohms for audio and 100 ohms for data. The big numbers are for open-wire line with huge (by modern standards) spacing. Modern plastic-insulated twisted pairs tend to fall, as you say, around 100 ohms. While I believe the characteristic impedance of open wire lines is higher than that of cables, as you say, that is far from the entire story. The characteristic impedance of cable is greatly dependent on frequency as a result of not having the correct ratio of inductance to capacitance. Once you're above the corner frequency, this is no longer true, until the frequency is very high. See: http://www.prc68.com/I/Zo.shtml Please note the second paragraph in the above referenced web page which states, "It turns out the the "100 Ohm" UTP cable does have a characteristic impedance near 600 Ohms at 1 kHz." Note also that the "corner frequency" for UTP is about 51 kHz, while this discussion concerns the characteristic impedance at audio frequencies which are well below 51 kHz. This is the reason I used the word "ultrasonic", rather than "RF", to refer to frequencies above the audio band. As a point of interest, the "standard" cable that started this discussion has a "corner frequency" of about 13.7 kHz if I pushed the buttons on my calculator correctly. It's the open wire lines that have the 600 ohm impedance. That is what they were using in the early days of telephone, and we inherited that 600 ohm legacy for telephone equipment for many years. The example of an open wire line given on the web page referenced is of a pair of 6 gauge (!!) wires, 1 foot apart. The result is that the characteristic impedance of cable varies with frequency, being lower at ultrasonic frequencies than at lower audio frequencies. If the above referenced web page is to be believed, then it appears that 600 Ohms is also a good approximation for the characteristic impedance of "100 Ohm UTP" in the audio band. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#91
Posted to rec.audio.tubes
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The decibel
John Byrns wrote: Please note the second paragraph in the above referenced web page which states, "It turns out the the "100 Ohm" UTP cable does have a characteristic impedance near 600 Ohms at 1 kHz." And the relevance of this to say a 1 km or 5 km run of cable is ? How many times do you have to be told ? Short runs are not 'transmission lines'. Graham |
#92
Posted to rec.audio.tubes
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The decibel
John Byrns wrote: If the above referenced web page is to be believed, then it appears that 600 Ohms is also a good approximation for the characteristic impedance of "100 Ohm UTP" in the audio band. At what cable length ? Graham |
#93
Posted to rec.audio.tubes
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The decibel
On Thu, 23 Aug 2007 03:25:34 +0100, Eeyore
wrote: Short runs are not 'transmission lines'. And characteristic impedances are defined (circularly, but that's the deal) as infinitely long (or terminated in the characteristic impedance). There is no such critter as a length variable in characteristic impedance. It's a function of geometry and a coupla materials variables. Such a messy thread that Angels fear to tread, but transmission line losses are only resistive at DC, and are complicated (frequency-sensitive) into matched loading. Into unmatched loading, they're beyond Usenet generalzation. Thanks, as always, Chris Hornbeck "It's just this little Chromium Switch. You people are SO superstitious." |
#94
Posted to rec.audio.tubes
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The decibel
In article ,
Eeyore wrote: John Byrns wrote: Please note the second paragraph in the above referenced web page which states, "It turns out the the "100 Ohm" UTP cable does have a characteristic impedance near 600 Ohms at 1 kHz." And the relevance of this to say a 1 km or 5 km run of cable is ? My example was a 5 mile local loop, not 5 km. Are you still trying to tell me that a 5 mile, or even 5 km, local loop, or run of "UTP" cable, is no different than a simple resistor whose resistance is equal to the DC loop resistance of the cable? How many times do you have to be told ? Short runs are not 'transmission lines'. You still haven't told us what a "transmission line" is, and how long a cable must be for you to consider it to be a "transmission line"? Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#95
Posted to rec.audio.tubes
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The decibel
In article ,
Eeyore wrote: John Byrns wrote: If the above referenced web page is to be believed, then it appears that 600 Ohms is also a good approximation for the characteristic impedance of "100 Ohm UTP" in the audio band. At what cable length ? Any length. The characteristic impedance is independent of length because it is defined in terms of the cables R, L, C, & G per unit length, where the unit length is your choice. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#96
Posted to rec.audio.tubes
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The decibel
John Byrns wrote: Eeyore wrote: John Byrns wrote: Please note the second paragraph in the above referenced web page which states, "It turns out the the "100 Ohm" UTP cable does have a characteristic impedance near 600 Ohms at 1 kHz." And the relevance of this to say a 1 km or 5 km run of cable is ? My example was a 5 mile local loop, not 5 km. Do you normally pick nits ? 5 mi = 8km more or less. The 'mile' is only used in 2 developed countries worlwide (and only for motoring in one of them) out of hundreds who use metric measure. Do you have an aversion to using international standard (SI) units ? Are you still trying to tell me that a 5 mile, or even 5 km, local loop, or run of "UTP" cable, is no different than a simple resistor whose resistance is equal to the DC loop resistance of the cable? No, I never ever said that. What I implied (correctly) was that for shorter lengths, the DC resisitive losses in real telephone cables at audio frequencies dominate the attenuation figures. I simply never mentioned the other aspects (to avoid unnecessary and pointless complexity). How many times do you have to be told ? Short runs are not 'transmission lines'. You still haven't told us what a "transmission line" is, and how long a cable must be for you to consider it to be a "transmission line"? How long is a piece of string ? In order for a cable to even begin to behave as a transmission line, its length must be some modest fraction of the highest frequency's wavelength. For telephones. the highest frequency of interest is 4kHz and its wavelength is 75km. I suggest you also wake up to the idea that twisted pair cables are not some fanciful '600 ohm' circuit. Graham |
#97
Posted to rec.audio.tubes
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The decibel
John Byrns wrote: Eeyore wrote: John Byrns wrote: If the above referenced web page is to be believed, then it appears that 600 Ohms is also a good approximation for the characteristic impedance of "100 Ohm UTP" in the audio band. At what cable length ? Any length. 1 metre ? You're an utter ****WIT ! I suggest you depart this group with your head held in shame for being a total cretin. Graham |
#98
Posted to rec.audio.tubes
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The decibel
On Wed, 22 Aug 2007 17:16:51 -0500, John Byrns
wrote: In article , The Phantom wrote: On Wed, 22 Aug 2007 15:58:52 GMT, John Byrns wrote: In article , Chris Hornbeck wrote: On Wed, 22 Aug 2007 03:15:13 +0100, Eeyore wrote: Do you think it is higher or lower than 600 ohms? I was under the impression it could be lower but I see the standards still refer to 600 ohms. The characteristic impedance of the twisted pair cable is actually around 100 ohms and DSL circuits operate at this impedance. So it's 600 ohms for audio and 100 ohms for data. The big numbers are for open-wire line with huge (by modern standards) spacing. Modern plastic-insulated twisted pairs tend to fall, as you say, around 100 ohms. While I believe the characteristic impedance of open wire lines is higher than that of cables, as you say, that is far from the entire story. The characteristic impedance of cable is greatly dependent on frequency as a result of not having the correct ratio of inductance to capacitance. Once you're above the corner frequency, this is no longer true, until the frequency is very high. See: http://www.prc68.com/I/Zo.shtml Please note the second paragraph in the above referenced web page which states, "It turns out the the "100 Ohm" UTP cable does have a characteristic impedance near 600 Ohms at 1 kHz." Note also that the "corner frequency" for UTP is about 51 kHz, while this discussion concerns the characteristic impedance at audio frequencies You made an unqualified statement that "The characteristic impedance of cable is greatly dependent on frequency as a result of not having the correct ratio of inductance to capacitance." It is true that the discussion had concerned voice band frequencies, but I felt that it should be emphasized that your unqualified statement wasn't really true for all frequencies. All of my posts until now have concerned early telephone transmission lines, and I have been at pains to point out that the 600 ohms was a characteristic of open wire lines. The corner frequency of the open wire line mentioned on the cited web page is 194 Hz, so the 600 ohm impedance is fairly constant across the standard telephone voice band. But this is not the case for CAT5 cable, for example. Nobody had yet pointed out that transmission line impedance behaves very differently below the corner frequency than above it. For example, if you use the values for R, L, G, and C for CAT5 from the web page cited, and calculate the Zo for a number of frequencies, you get (using for "angle"): Frequency Zo 20 Hz 5508.1 -44.989 degrees 100 Hz 2463.3 -44.944 1000 Hz 779.0 -44.439 10000 Hz 249.7 -39.460 20000 Hz 180.5 -34.306 51000 Hz 129.7 -22.518 100000 Hz 115.5 -13.525 1000000 Hz 109.1 -1.462 10000000 Hz 109.0 -0.146 100000000 Hz 109.0 -0.015 Eeyore said in another post that "The characteristic impedance of the twisted pair cable is actually around 100 ohms and DSL circuits operate at this impedance. So it's 600 ohms for audio and 100 ohms for data." SNIP And, you said: If the above referenced web page is to be believed, then it appears that 600 Ohms is also a good approximation for the characteristic impedance of "100 Ohm UTP" in the audio band. Apparently not, with 5508 ohms at 20 Hz and 180.5 ohms at 20000 Hz. Even in the telephone voice band with an impedance of 1422 ohms at 300 Hz and 450 ohms at 3000 Hz, I wouldn't call 600 ohms a "good" approximation. These numbers are for CAT5; UTP may be a little different, but it will still have a substantial variation in impedance over the audio band. In fact, you yourself said, "The characteristic impedance of cable is greatly dependent on frequency...", referring to frequencies below the corner frequency of the cable. If this is so, then no single impedance is going to be a good approximation of the cable impedance in the audio band. The fact that UTP has an impedance of "...near 600 ohms at 1 kHz." (as the web page says) has no connection to the fact that the early 20th century open wire lines had an impedance of ~600 ohms. The early lines were being operated above their corner frequency, where they behaved like "proper" transmission lines, with a Zo over the telephone band that was much more constant than twisted pair. Calculating the Zo of the open wire line whose parameters are given on the cited web page: Frequency Zo 300 Hz 662.3 -16.45 degrees 800 Hz 615.6 -6.82 1500 Hz 609.4 -3.69 3000 Hz 607.5 -1.85 All this got going because Iain mistakenly equated the loss of 1 mile of phone line with 1 bel. We now know he was off by a factor of 10. Regards, John Byrns |
#99
Posted to rec.audio.tubes
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The decibel
"John Byrns" wrote in message ... In article , Eeyore wrote: John Byrns wrote: Please note the second paragraph in the above referenced web page which states, "It turns out the the "100 Ohm" UTP cable does have a characteristic impedance near 600 Ohms at 1 kHz." And the relevance of this to say a 1 km or 5 km run of cable is ? My example was a 5 mile local loop, not 5 km. Are you still trying to tell me that a 5 mile, or even 5 km, local loop, or run of "UTP" cable, is no different than a simple resistor whose resistance is equal to the DC loop resistance of the cable? No, but how significant length is depends on the signal frequency. How many times do you have to be told ? Short runs are not 'transmission lines'. You still haven't told us what a "transmission line" is, and how long a cable must be for you to consider it to be a "transmission line"? The really picky folks on the Usenet audio jury say that to be a transmission line, the line has to be 1/8 or more of a wavelength long at the highest frequency transmitted. For a voice-grade signal topping out at say 4 KHz, a wavelength is about 46 miles, so anything up to about 6 miles is most definitely not a transmission line. For high fidelity audio, drop that to abut 2 miles. |
#100
Posted to rec.audio.tubes
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The decibel
"Arny Krueger" The really picky folks on the Usenet audio jury say that to be a transmission line, the line has to be 1/8 or more of a wavelength long at the highest frequency transmitted. For a voice-grade signal topping out at say 4 KHz, a wavelength is about 46 miles, so anything up to about 6 miles is most definitely not a transmission line. For high fidelity audio, drop that to abut 2 miles. ** Then, there are the relatively SANE folk who see * that extreme position * as being extraordinarily pedantic, artificial and entirely foolish. The most perspicacious of that latter group assert that this position is blatant heresy, promulgated by a subset of the RF fraternity - particularly the great unwashed, smelly and un-educated " ham radio " rabble. Well, **** them - hams are just pigs with a bad attitude. Co-axial, twisted pair and even twin-line cables all exhibit " characteristic impedance" phenomena at lengths that are FAR , FAR shorter than that needed for standing wave effects. Distributed capacitance, inductance and resistive losses are very significant at high audio frequencies, even with cables of only a few metres, if the load impedance is that of a ES loudspeaker. 500 metres of unloaded, shielded twisted pair mic cable exhibits all the debilitating effects of a badly terminated transmission line - despite the shortest wavelength being a TINY fraction its length. Either DO some simple bench tests, or do the maths on a good simulator. Correctly terminating audio cables does wonders for their flat response bandwidth. Failing to do so can bite, sometimes very hard. ........ Phil |
#101
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The decibel
On Thu, 23 Aug 2007 08:10:04 -0400, "Arny Krueger"
wrote: "John Byrns" wrote in message ... In article , Eeyore wrote: John Byrns wrote: Please note the second paragraph in the above referenced web page which states, "It turns out the the "100 Ohm" UTP cable does have a characteristic impedance near 600 Ohms at 1 kHz." And the relevance of this to say a 1 km or 5 km run of cable is ? My example was a 5 mile local loop, not 5 km. Are you still trying to tell me that a 5 mile, or even 5 km, local loop, or run of "UTP" cable, is no different than a simple resistor whose resistance is equal to the DC loop resistance of the cable? No, but how significant length is depends on the signal frequency. How many times do you have to be told ? Short runs are not 'transmission lines'. You still haven't told us what a "transmission line" is, and how long a cable must be for you to consider it to be a "transmission line"? The really picky folks on the Usenet audio jury say that to be a transmission line, the line has to be 1/8 or more of a wavelength long at the highest frequency transmitted. For a voice-grade signal topping out at say 4 KHz, a wavelength is about 46 miles, so anything up to about 6 miles is most definitely not a transmission line. For high fidelity audio, drop that to abut 2 miles. This would be about right for that open wire line consisting of a pair of 6 gauge conductors spaced 1 foot apart. For a twisted pair of 19 gauge or 22 gauge, the velocity of propagation is significantly lower, and your numbers would be much smaller. |
#102
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The decibel
In article ,
The Phantom wrote: On Wed, 22 Aug 2007 17:16:51 -0500, John Byrns wrote: In article , The Phantom wrote: On Wed, 22 Aug 2007 15:58:52 GMT, John Byrns wrote: In article , Chris Hornbeck wrote: On Wed, 22 Aug 2007 03:15:13 +0100, Eeyore wrote: Do you think it is higher or lower than 600 ohms? I was under the impression it could be lower but I see the standards still refer to 600 ohms. The characteristic impedance of the twisted pair cable is actually around 100 ohms and DSL circuits operate at this impedance. So it's 600 ohms for audio and 100 ohms for data. The big numbers are for open-wire line with huge (by modern standards) spacing. Modern plastic-insulated twisted pairs tend to fall, as you say, around 100 ohms. While I believe the characteristic impedance of open wire lines is higher than that of cables, as you say, that is far from the entire story. The characteristic impedance of cable is greatly dependent on frequency as a result of not having the correct ratio of inductance to capacitance. Once you're above the corner frequency, this is no longer true, until the frequency is very high. See: http://www.prc68.com/I/Zo.shtml Please note the second paragraph in the above referenced web page which states, "It turns out the the "100 Ohm" UTP cable does have a characteristic impedance near 600 Ohms at 1 kHz." Note also that the "corner frequency" for UTP is about 51 kHz, while this discussion concerns the characteristic impedance at audio frequencies You made an unqualified statement that "The characteristic impedance of cable is greatly dependent on frequency as a result of not having the correct ratio of inductance to capacitance." It is true that the discussion had concerned voice band frequencies, but I felt that it should be emphasized that your unqualified statement wasn't really true for all frequencies. All of my posts until now have concerned early telephone transmission lines, and I have been at pains to point out that the 600 ohms was a characteristic of open wire lines. The corner frequency of the open wire line mentioned on the cited web page is 194 Hz, so the 600 ohm impedance is fairly constant across the standard telephone voice band. But this is not the case for CAT5 cable, for example. Nobody had yet pointed out that transmission line impedance behaves very differently below the corner frequency than above it. For example, if you use the values for R, L, G, and C for CAT5 from the web page cited, and calculate the Zo for a number of frequencies, you get (using for "angle"): Frequency Zo 20 Hz 5508.1 -44.989 degrees 100 Hz 2463.3 -44.944 1000 Hz 779.0 -44.439 10000 Hz 249.7 -39.460 20000 Hz 180.5 -34.306 51000 Hz 129.7 -22.518 100000 Hz 115.5 -13.525 1000000 Hz 109.1 -1.462 10000000 Hz 109.0 -0.146 100000000 Hz 109.0 -0.015 Eeyore said in another post that "The characteristic impedance of the twisted pair cable is actually around 100 ohms and DSL circuits operate at this impedance. So it's 600 ohms for audio and 100 ohms for data." SNIP And, you said: If the above referenced web page is to be believed, then it appears that 600 Ohms is also a good approximation for the characteristic impedance of "100 Ohm UTP" in the audio band. Apparently not, with 5508 ohms at 20 Hz and 180.5 ohms at 20000 Hz. Even in the telephone voice band with an impedance of 1422 ohms at 300 Hz and 450 ohms at 3000 Hz, I wouldn't call 600 ohms a "good" approximation. These numbers are for CAT5; UTP may be a little different, but it will still have a substantial variation in impedance over the audio band. In fact, you yourself said, "The characteristic impedance of cable is greatly dependent on frequency...", referring to frequencies below the corner frequency of the cable. If this is so, then no single impedance is going to be a good approximation of the cable impedance in the audio band. The fact that UTP has an impedance of "...near 600 ohms at 1 kHz." (as the web page says) has no connection to the fact that the early 20th century open wire lines had an impedance of ~600 ohms. The early lines were being operated above their corner frequency, where they behaved like "proper" transmission lines, with a Zo over the telephone band that was much more constant than twisted pair. Calculating the Zo of the open wire line whose parameters are given on the cited web page: Frequency Zo 300 Hz 662.3 -16.45 degrees 800 Hz 615.6 -6.82 1500 Hz 609.4 -3.69 3000 Hz 607.5 -1.85 All this got going because Iain mistakenly equated the loss of 1 mile of phone line with 1 bel. We now know he was off by a factor of 10. Since several posters have mentioned open wire line, it is worth mentioning that the "standard telephone line" Iain was referring to was probably 19 gauge cable, not open wire line, as open wire line has a loss much lower than 1 decibel per mile. Relative to the considerable variation in the characteristic impedance of telephone cables vs. frequency, I pointed this out and indicated how advantage could be taken of the variation in the characteristic impedance vs. frequency to help equalize short loops by terminating the line in its characteristic impedance at the high end of the band, rather than terminating it with the "600 Ohm" midband impedance. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#103
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The decibel
In article ,
"Arny Krueger" wrote: "John Byrns" wrote in message ... In article , Eeyore wrote: John Byrns wrote: Please note the second paragraph in the above referenced web page which states, "It turns out the the "100 Ohm" UTP cable does have a characteristic impedance near 600 Ohms at 1 kHz." And the relevance of this to say a 1 km or 5 km run of cable is ? My example was a 5 mile local loop, not 5 km. Are you still trying to tell me that a 5 mile, or even 5 km, local loop, or run of "UTP" cable, is no different than a simple resistor whose resistance is equal to the DC loop resistance of the cable? No, but how significant length is depends on the signal frequency. How many times do you have to be told ? Short runs are not 'transmission lines'. You still haven't told us what a "transmission line" is, and how long a cable must be for you to consider it to be a "transmission line"? The really picky folks on the Usenet audio jury say that to be a transmission line, the line has to be 1/8 or more of a wavelength long at the highest frequency transmitted. Thanks Arny, finally someone offers a number for how long a line must be to be considered a "transmission line", I wonder what Eyeore thinks of this number? For a voice-grade signal topping out at say 4 KHz, a wavelength is about 46 miles, so anything up to about 6 miles is most definitely not a transmission line. For high fidelity audio, drop that to abut 2 miles. You are forgetting that the propagation velocity of a wave in the "standard telephone line" cable, that Iain mentioned in the original version of his "decibel" web page, is about one quarter the speed of light in free space. That makes a wavelength at 4 kHz somewhere in the eleven to twelve mile range, using your 1/8 wavelength factor that would make any length of this cable over about 1.5 miles long a "transmission line", and shorter for Hi-Fi audio. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#104
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The decibel
"John Byrns" wrote in message
In article , "Arny Krueger" wrote: "John Byrns" wrote in message ... In article , Eeyore wrote: John Byrns wrote: Please note the second paragraph in the above referenced web page which states, "It turns out the the "100 Ohm" UTP cable does have a characteristic impedance near 600 Ohms at 1 kHz." And the relevance of this to say a 1 km or 5 km run of cable is ? My example was a 5 mile local loop, not 5 km. Are you still trying to tell me that a 5 mile, or even 5 km, local loop, or run of "UTP" cable, is no different than a simple resistor whose resistance is equal to the DC loop resistance of the cable? No, but how significant length is depends on the signal frequency. How many times do you have to be told ? Short runs are not 'transmission lines'. You still haven't told us what a "transmission line" is, and how long a cable must be for you to consider it to be a "transmission line"? The really picky folks on the Usenet audio jury say that to be a transmission line, the line has to be 1/8 or more of a wavelength long at the highest frequency transmitted. Thanks Arny, finally someone offers a number for how long a line must be to be considered a "transmission line", I wonder what Eyeore thinks of this number? For a voice-grade signal topping out at say 4 KHz, a wavelength is about 46 miles, so anything up to about 6 miles is most definitely not a transmission line. For high fidelity audio, drop that to abut 2 miles. You are forgetting that the propagation velocity of a wave in the "standard telephone line" cable, that Iain mentioned in the original version of his "decibel" web page, is about one quarter the speed of light in free space. Yeah, I forgot propigation delay, but my sources say that the propigation coefficient of UTP 24 gauge is more like 70% than 25%. |
#105
Posted to rec.audio.tubes
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The decibel
In article ,
"Arny Krueger" wrote: "John Byrns" wrote in message In article , "Arny Krueger" wrote: "John Byrns" wrote in message ... In article , Eeyore wrote: John Byrns wrote: Please note the second paragraph in the above referenced web page which states, "It turns out the the "100 Ohm" UTP cable does have a characteristic impedance near 600 Ohms at 1 kHz." And the relevance of this to say a 1 km or 5 km run of cable is ? My example was a 5 mile local loop, not 5 km. Are you still trying to tell me that a 5 mile, or even 5 km, local loop, or run of "UTP" cable, is no different than a simple resistor whose resistance is equal to the DC loop resistance of the cable? No, but how significant length is depends on the signal frequency. How many times do you have to be told ? Short runs are not 'transmission lines'. You still haven't told us what a "transmission line" is, and how long a cable must be for you to consider it to be a "transmission line"? The really picky folks on the Usenet audio jury say that to be a transmission line, the line has to be 1/8 or more of a wavelength long at the highest frequency transmitted. Thanks Arny, finally someone offers a number for how long a line must be to be considered a "transmission line", I wonder what Eyeore thinks of this number? For a voice-grade signal topping out at say 4 KHz, a wavelength is about 46 miles, so anything up to about 6 miles is most definitely not a transmission line. For high fidelity audio, drop that to abut 2 miles. You are forgetting that the propagation velocity of a wave in the "standard telephone line" cable, that Iain mentioned in the original version of his "decibel" web page, is about one quarter the speed of light in free space. Yeah, I forgot propigation delay, but my sources say that the propigation coefficient of UTP 24 gauge is more like 70% than 25%. That may well be correct, the approx. 25% figure I gave is for the "standard telephone line" that Iain referred to on the first version of his web page. I am surprised though that the wave velocity is so different in the old 19 gauge cable vs. 24 gauge UTP. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#106
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The decibel
On Thu, 23 Aug 2007 15:11:49 -0400, "Arny Krueger"
wrote: "John Byrns" wrote in message In article , "Arny Krueger" wrote: "John Byrns" wrote in message ... In article , Eeyore wrote: John Byrns wrote: Please note the second paragraph in the above referenced web page which states, "It turns out the the "100 Ohm" UTP cable does have a characteristic impedance near 600 Ohms at 1 kHz." And the relevance of this to say a 1 km or 5 km run of cable is ? My example was a 5 mile local loop, not 5 km. Are you still trying to tell me that a 5 mile, or even 5 km, local loop, or run of "UTP" cable, is no different than a simple resistor whose resistance is equal to the DC loop resistance of the cable? No, but how significant length is depends on the signal frequency. How many times do you have to be told ? Short runs are not 'transmission lines'. You still haven't told us what a "transmission line" is, and how long a cable must be for you to consider it to be a "transmission line"? The really picky folks on the Usenet audio jury say that to be a transmission line, the line has to be 1/8 or more of a wavelength long at the highest frequency transmitted. Thanks Arny, finally someone offers a number for how long a line must be to be considered a "transmission line", I wonder what Eyeore thinks of this number? For a voice-grade signal topping out at say 4 KHz, a wavelength is about 46 miles, so anything up to about 6 miles is most definitely not a transmission line. For high fidelity audio, drop that to abut 2 miles. You are forgetting that the propagation velocity of a wave in the "standard telephone line" cable, that Iain mentioned in the original version of his "decibel" web page, is about one quarter the speed of light in free space. Yeah, I forgot propigation delay, but my sources say that the propigation coefficient of UTP 24 gauge is more like 70% than 25%. This is only true at high frequencies. The classic condition for "distortionless" transmission is for the line parameters R, L, G and C to be related as: L C - = - R G Since most real cables have G essentially zero at low frequencies, this causes the propagation delay to vary with frequency in the audio band. However, modern cables are probably better in this respect than the 1925 cables whose properties I copied out of the old book I've been referencing, but their Zo and propagation delay still vary with frequency. Both of these effects are due to the above relationship not being met. |
#107
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The decibel
On Thu, 23 Aug 2007 14:14:53 GMT, John Byrns wrote:
In article , The Phantom wrote: On Wed, 22 Aug 2007 17:16:51 -0500, John Byrns wrote: In article , The Phantom wrote: On Wed, 22 Aug 2007 15:58:52 GMT, John Byrns wrote: In article , Chris Hornbeck wrote: On Wed, 22 Aug 2007 03:15:13 +0100, Eeyore wrote: Do you think it is higher or lower than 600 ohms? I was under the impression it could be lower but I see the standards still refer to 600 ohms. The characteristic impedance of the twisted pair cable is actually around 100 ohms and DSL circuits operate at this impedance. So it's 600 ohms for audio and 100 ohms for data. The big numbers are for open-wire line with huge (by modern standards) spacing. Modern plastic-insulated twisted pairs tend to fall, as you say, around 100 ohms. While I believe the characteristic impedance of open wire lines is higher than that of cables, as you say, that is far from the entire story. The characteristic impedance of cable is greatly dependent on frequency as a result of not having the correct ratio of inductance to capacitance. Once you're above the corner frequency, this is no longer true, until the frequency is very high. See: http://www.prc68.com/I/Zo.shtml Please note the second paragraph in the above referenced web page which states, "It turns out the the "100 Ohm" UTP cable does have a characteristic impedance near 600 Ohms at 1 kHz." Note also that the "corner frequency" for UTP is about 51 kHz, while this discussion concerns the characteristic impedance at audio frequencies You made an unqualified statement that "The characteristic impedance of cable is greatly dependent on frequency as a result of not having the correct ratio of inductance to capacitance." It is true that the discussion had concerned voice band frequencies, but I felt that it should be emphasized that your unqualified statement wasn't really true for all frequencies. All of my posts until now have concerned early telephone transmission lines, and I have been at pains to point out that the 600 ohms was a characteristic of open wire lines. The corner frequency of the open wire line mentioned on the cited web page is 194 Hz, so the 600 ohm impedance is fairly constant across the standard telephone voice band. But this is not the case for CAT5 cable, for example. Nobody had yet pointed out that transmission line impedance behaves very differently below the corner frequency than above it. For example, if you use the values for R, L, G, and C for CAT5 from the web page cited, and calculate the Zo for a number of frequencies, you get (using for "angle"): Frequency Zo 20 Hz 5508.1 -44.989 degrees 100 Hz 2463.3 -44.944 1000 Hz 779.0 -44.439 10000 Hz 249.7 -39.460 20000 Hz 180.5 -34.306 51000 Hz 129.7 -22.518 100000 Hz 115.5 -13.525 1000000 Hz 109.1 -1.462 10000000 Hz 109.0 -0.146 100000000 Hz 109.0 -0.015 Eeyore said in another post that "The characteristic impedance of the twisted pair cable is actually around 100 ohms and DSL circuits operate at this impedance. So it's 600 ohms for audio and 100 ohms for data." SNIP And, you said: If the above referenced web page is to be believed, then it appears that 600 Ohms is also a good approximation for the characteristic impedance of "100 Ohm UTP" in the audio band. Apparently not, with 5508 ohms at 20 Hz and 180.5 ohms at 20000 Hz. Even in the telephone voice band with an impedance of 1422 ohms at 300 Hz and 450 ohms at 3000 Hz, I wouldn't call 600 ohms a "good" approximation. These numbers are for CAT5; UTP may be a little different, but it will still have a substantial variation in impedance over the audio band. In fact, you yourself said, "The characteristic impedance of cable is greatly dependent on frequency...", referring to frequencies below the corner frequency of the cable. If this is so, then no single impedance is going to be a good approximation of the cable impedance in the audio band. The fact that UTP has an impedance of "...near 600 ohms at 1 kHz." (as the web page says) has no connection to the fact that the early 20th century open wire lines had an impedance of ~600 ohms. The early lines were being operated above their corner frequency, where they behaved like "proper" transmission lines, with a Zo over the telephone band that was much more constant than twisted pair. Calculating the Zo of the open wire line whose parameters are given on the cited web page: Frequency Zo 300 Hz 662.3 -16.45 degrees 800 Hz 615.6 -6.82 1500 Hz 609.4 -3.69 3000 Hz 607.5 -1.85 All this got going because Iain mistakenly equated the loss of 1 mile of phone line with 1 bel. We now know he was off by a factor of 10. Since several posters have mentioned open wire line, it is worth mentioning that the "standard telephone line" Iain was referring to was probably 19 gauge cable, not open wire line, as open wire line has a loss much lower than 1 decibel per mile. I'm sure that was what was meant by "standard telephone line". That was what was described in the paragraph I copied out of the old Bell Labs book in my first post in this thread: "Standard cable is defined as a cable having uniformly distributed resistances of 88 ohms per loop mile and uniformly distributed shunt capacitance of .054 microfarad per mile. Its series inductance and shunt leakance are assumed to be zero." The 88 ohms per loop mile corresponds to 19 gauge wire. This is the cable that has .947 dB loss per mile as shown in the table I copied out of the book. And it's true that open wire line has much less loss. Terman's "Radio Engineers' Handbook" has a chart showing the loss of two wire open line. A line composed of 12 gauge wire with separation to give 600 ohms has an attenuation of .01 dB per 1000 feet. You can see why before repeaters were practical they were using 6 gauge wire for long distance lines. The book describes the earliest repeater amplifiers as consisting of a telephone receiver (earpiece) with a microphone (carbon button) mechanically connected to the diaphragm. They say, "The tendency of microphone buttons to "breathe", due to heating and packing, and the distortion inherent in carbon buttons make even the best-designed of such devices difficult to maintain when several are operated in one system." I can just imagine! Relative to the considerable variation in the characteristic impedance of telephone cables vs. frequency, I pointed this out and indicated how advantage could be taken of the variation in the characteristic impedance vs. frequency to help equalize short loops by terminating the line in its characteristic impedance at the high end of the band, rather than terminating it with the "600 Ohm" midband impedance. What I was getting at is that with the substantial variation in Zo in the audio band, your statement "it appears that 600 Ohms is also a good approximation for the characteristic impedance of "100 Ohm UTP" in the audio band." rather stretches the meaning of "good approximation". Regards, John Byrns |
#108
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The decibel
On Thu, 23 Aug 2007 15:36:26 -0500, John Byrns
wrote: In article , "Arny Krueger" wrote: "John Byrns" wrote in message In article , "Arny Krueger" wrote: "John Byrns" wrote in message ... In article , Eeyore wrote: John Byrns wrote: Please note the second paragraph in the above referenced web page which states, "It turns out the the "100 Ohm" UTP cable does have a characteristic impedance near 600 Ohms at 1 kHz." And the relevance of this to say a 1 km or 5 km run of cable is ? My example was a 5 mile local loop, not 5 km. Are you still trying to tell me that a 5 mile, or even 5 km, local loop, or run of "UTP" cable, is no different than a simple resistor whose resistance is equal to the DC loop resistance of the cable? No, but how significant length is depends on the signal frequency. How many times do you have to be told ? Short runs are not 'transmission lines'. You still haven't told us what a "transmission line" is, and how long a cable must be for you to consider it to be a "transmission line"? The really picky folks on the Usenet audio jury say that to be a transmission line, the line has to be 1/8 or more of a wavelength long at the highest frequency transmitted. Thanks Arny, finally someone offers a number for how long a line must be to be considered a "transmission line", I wonder what Eyeore thinks of this number? For a voice-grade signal topping out at say 4 KHz, a wavelength is about 46 miles, so anything up to about 6 miles is most definitely not a transmission line. For high fidelity audio, drop that to abut 2 miles. You are forgetting that the propagation velocity of a wave in the "standard telephone line" cable, that Iain mentioned in the original version of his "decibel" web page, is about one quarter the speed of light in free space. Yeah, I forgot propigation delay, but my sources say that the propigation coefficient of UTP 24 gauge is more like 70% than 25%. That may well be correct, the approx. 25% figure I gave is for the "standard telephone line" that Iain referred to on the first version of his web page. I am surprised though that the wave velocity is so different in the old 19 gauge cable vs. 24 gauge UTP. I suspect the velocity Arny cited isn't for the audio band, whereas the figure for the old 19 gauge cable was for the telephone voice band. Regards, John Byrns |
#109
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The decibel
Phil Allison wrote: Distributed capacitance, inductance and resistive losses are very significant at high audio frequencies, even with cables of only a few metres, if the load impedance is that of a ES loudspeaker. Yet modelling them as 'transmission lines' will make us none the wiser. The specific losses need to be considered according to application. Graham |
#110
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The decibel
John Byrns wrote: "Arny Krueger" wrote: Yeah, I forgot propigation delay, but my sources say that the propigation coefficient of UTP 24 gauge is more like 70% than 25%. That may well be correct, the approx. 25% figure I gave is for the "standard telephone line" that Iain referred to on the first version of his web page. Actually, that's a *telegraph* line. It has no meaningful relationship whatever to modern audio circuits of any type. I suggest you forget it. This is the trouble with using 1920's thinking. Graham |
#111
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The decibel
"Eeysore ****ing SNIPPING Idiot " Phil Allison wrote: ** A lot more than this one para: Distributed capacitance, inductance and resistive losses are very significant at high audio frequencies, even with cables of only a few metres, if the load impedance is that of a ES loudspeaker. Yet modelling them as 'transmission lines' will make us none the wiser. ** False assertion. Another one from the donkey brain TROLL. **Here is what I wrote; Co-axial, twisted pair and even twin-line cables all exhibit " characteristic impedance" phenomena at lengths that are FAR , FAR shorter than that needed for standing wave effects. Distributed capacitance, inductance and resistive losses are very significant at high audio frequencies, even with cables of only a few metres, if the load impedance is that of a ES loudspeaker. 500 metres of unloaded, shielded twisted pair mic cable exhibits all the debilitating effects of a badly terminated transmission line - despite the shortest wavelength being a TINY fraction its length. Either DO some simple bench tests, or do the maths on a good simulator. Correctly terminating audio cables does wonders for their flat response bandwidth. Failing to do so can bite, sometimes very hard. ........ Phil |
#112
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The decibel
In article ,
Eeyore wrote: Phil Allison wrote: Distributed capacitance, inductance and resistive losses are very significant at high audio frequencies, even with cables of only a few metres, if the load impedance is that of a ES loudspeaker. Yet modelling them as 'transmission lines' will make us none the wiser. How do you suggest modeling telephone cables if not as "transmission lines"? What do you suggest, depending on measurements only? Measurements may tell us how a line works as we have connected it, but it fails to give us any insight into how the line actually works. I think the real problem here is that you are incapable of becoming any wiser than you currently are. The specific losses need to be considered according to application. As Hyundai would say "Duh". Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#113
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The decibel
In article ,
Eeyore wrote: John Byrns wrote: "Arny Krueger" wrote: Yeah, I forgot propigation delay, but my sources say that the propigation coefficient of UTP 24 gauge is more like 70% than 25%. That may well be correct, the approx. 25% figure I gave is for the "standard telephone line" that Iain referred to on the first version of his web page. Actually, that's a *telegraph* line. On what basis do you call it a "telegraph line" when Iain specifically said it was a "standard telephone line"? The cable I found that most closely matched Iain's description was a 19 gauge telephone toll cable, which is the cable the 25% factor I quoted applies to. On the other hand what if it is a "telegraph line", is there any real difference between telephone cables and telegraph cables, I am fairly certain that they both operate on the same principles? Furthermore it is my understanding that "telegraph" cables have been utilized for the transmission of audio signals, and that the Telegraph Company has leased "telephone lines" from the Telephone Company to use for transmitting telegraph signals. It has no meaningful relationship whatever to modern audio circuits of any type. I suggest you forget it. This is the trouble with using 1920's thinking. How did you come to that conclusion, my telephone still depends on a mile or two of cable to connect it to the RT, although admittedly beyond that point the world becomes mostly fiber? What is wrong with 1920s thinking? Those old guys weren't as dumb as you would have us believe, and to the best of my knowledge the "1920s" theory still holds, the laws of physics haven't yet been repealed. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#114
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The decibel
John Byrns wrote: Eeyore wrote: John Byrns wrote: "Arny Krueger" wrote: Yeah, I forgot propigation delay, but my sources say that the propigation coefficient of UTP 24 gauge is more like 70% than 25%. That may well be correct, the approx. 25% figure I gave is for the "standard telephone line" that Iain referred to on the first version of his web page. Actually, that's a *telegraph* line. On what basis do you call it a "telegraph line" when Iain specifically said it was a "standard telephone line"? Because early long distance telephony used the very widely separated telegraph line conctruction which does indeed produce a 600 ohm characteristic impedance. Are you trying to suggest that this construction is STILL a "standard telephone line" ? Graham |
#115
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The decibel
In the '60s, there were two other balanced comms impedances knocking around:
900 and 1,200 Ohms, I encountered them as Z options in test-gear catalogs. Does anybody know what these were principally for? Jim "Eeyore" wrote in message ... John Byrns wrote: Eeyore wrote: John Byrns wrote: "Arny Krueger" wrote: Yeah, I forgot propigation delay, but my sources say that the propigation coefficient of UTP 24 gauge is more like 70% than 25%. That may well be correct, the approx. 25% figure I gave is for the "standard telephone line" that Iain referred to on the first version of his web page. Actually, that's a *telegraph* line. On what basis do you call it a "telegraph line" when Iain specifically said it was a "standard telephone line"? Because early long distance telephony used the very widely separated telegraph line conctruction which does indeed produce a 600 ohm characteristic impedance. Are you trying to suggest that this construction is STILL a "standard telephone line" ? Graham |
#116
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The decibel
In article ,
Eeyore wrote: John Byrns wrote: Eeyore wrote: John Byrns wrote: "Arny Krueger" wrote: Yeah, I forgot propigation delay, but my sources say that the propigation coefficient of UTP 24 gauge is more like 70% than 25%. That may well be correct, the approx. 25% figure I gave is for the "standard telephone line" that Iain referred to on the first version of his web page. Actually, that's a *telegraph* line. On what basis do you call it a "telegraph line" when Iain specifically said it was a "standard telephone line"? Because early long distance telephony used the very widely separated telegraph line conctruction which does indeed produce a 600 ohm characteristic impedance. If it is a line for telephony, then it is a telephone line even if it shares its basic method of construction with telegraph lines, you are making a silly semantic argument here. In any case if you look into the details of the line mentioned on Iain's web page it becomes obvious that the "standard telephone line" he was talking about was not an open wire line such as you are talking about, but was a 19 gauge toll cable. Are you trying to suggest that this construction is STILL a "standard telephone line" ? I'm not sure if this is a trick question or not, as I expect most new telephone cables, except for those used in the "last mile", are fiber optic cables. But assuming we are talking about copper cables, yes I expect that they still use the same basic construction, the main difference being the use of new and different insulating materials. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
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The decibel
John Byrns wrote: Eeyore wrote: John Byrns wrote: Eeyore wrote: John Byrns wrote: "Arny Krueger" wrote: Yeah, I forgot propigation delay, but my sources say that the propigation coefficient of UTP 24 gauge is more like 70% than 25%. That may well be correct, the approx. 25% figure I gave is for the "standard telephone line" that Iain referred to on the first version of his web page. Actually, that's a *telegraph* line. On what basis do you call it a "telegraph line" when Iain specifically said it was a "standard telephone line"? Because early long distance telephony used the very widely separated telegraph line conctruction which does indeed produce a 600 ohm characteristic impedance. If it is a line for telephony, then it is a telephone line even if it shares its basic method of construction with telegraph lines, you are making a silly semantic argument here. It's not semantic at all. It's fundamental. In any case if you look into the details of the line mentioned on Iain's web page it becomes obvious that the "standard telephone line" he was talking about was not an open wire line such as you are talking about, but was a 19 gauge toll cable. What's a 'toll cable' outside the USA ? Are you trying to suggest that this construction is STILL a "standard telephone line" ? I'm not sure if this is a trick question or not, as I expect most new telephone cables, except for those used in the "last mile", are fiber optic cables. But assuming we are talking about copper cables, yes I expect that they still use the same basic construction, the main difference being the use of new and different insulating materials. NO THEY DO NOT USE THE SAME CONSTRUCTION ! Have you even the tiniest idea what a telegraph line looks like ? Graham |
#118
Posted to rec.audio.tubes
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The decibel
In article ,
Eeyore wrote: John Byrns wrote: Eeyore wrote: John Byrns wrote: Eeyore wrote: John Byrns wrote: "Arny Krueger" wrote: Yeah, I forgot propigation delay, but my sources say that the propigation coefficient of UTP 24 gauge is more like 70% than 25%. That may well be correct, the approx. 25% figure I gave is for the "standard telephone line" that Iain referred to on the first version of his web page. Actually, that's a *telegraph* line. On what basis do you call it a "telegraph line" when Iain specifically said it was a "standard telephone line"? Because early long distance telephony used the very widely separated telegraph line conctruction which does indeed produce a 600 ohm characteristic impedance. If it is a line for telephony, then it is a telephone line even if it shares its basic method of construction with telegraph lines, you are making a silly semantic argument here. It's not semantic at all. It's fundamental. You seem to want to walk both sides of the street here, either they are the same, or they are fundamentally different, you can't have it both ways. In any case if you look into the details of the line mentioned on Iain's web page it becomes obvious that the "standard telephone line" he was talking about was not an open wire line such as you are talking about, but was a 19 gauge toll cable. What's a 'toll cable' outside the USA ? Ya got me, you could tell us what they are called in the UK? Are you trying to suggest that this construction is STILL a "standard telephone line" ? I'm not sure if this is a trick question or not, as I expect most new telephone cables, except for those used in the "last mile", are fiber optic cables. But assuming we are talking about copper cables, yes I expect that they still use the same basic construction, the main difference being the use of new and different insulating materials. NO THEY DO NOT USE THE SAME CONSTRUCTION ! OK, I can believe the construction of telephone cables has changed over the years, please describe the changes in the construction of telephone cables over the years, excluding the obvious change in the materials used for insulation? Have you even the tiniest idea what a telegraph line looks like ? Now it is back to open wire lines again, you really seem to have a thing for open wire lines. I don't have the slightest clue how to distinguish a telegraph line from a telephone line, I have always assumed that most of the open wire lines I have seen are telephone lines. I do know that the telephone company also used telegraphic signaling and transmitted telegraph signals over their telephone lines. Also I believe that the telegraph company here in the US leased some of their lines from the telephone company, at least in the latter days. But back to what telegraph lines look like, the only possible distinction I can think of is that telegraph lines may use a different transposition scheme than telephone lines, which use many different transposition schemes depending on the type of carrier system employed with them. Of course the telegraph lines we see in the old "Western movies" are only a single line with an earth return. So why don't you explain what a telegraph line actually looks like and how to distinguish it from a telephone line? Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#119
Posted to rec.audio.tubes
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The decibel
John Byrns wrote: Eeyore wrote: Have you even the tiniest idea what a telegraph line looks like ? Now it is back to open wire lines again, you really seem to have a thing for open wire lines. Because it's the only type of 'phone line' that has a characteristic impedance of 600 ohms. And *I* don't have a thing for 600 ohms, *YOU* do ! I don't have the slightest clue how to distinguish a telegraph line from a telephone line Speaks volumes about your ignorance. Graham |
#120
Posted to rec.audio.tubes
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The decibel
On Sat, 25 Aug 2007 14:07:29 GMT, John Byrns wrote:
In article , Eeyore wrote: John Byrns wrote: Eeyore wrote: John Byrns wrote: Eeyore wrote: John Byrns wrote: "Arny Krueger" wrote: Yeah, I forgot propigation delay, but my sources say that the propigation coefficient of UTP 24 gauge is more like 70% than 25%. That may well be correct, the approx. 25% figure I gave is for the "standard telephone line" that Iain referred to on the first version of his web page. Actually, that's a *telegraph* line. On what basis do you call it a "telegraph line" when Iain specifically said it was a "standard telephone line"? Because early long distance telephony used the very widely separated telegraph line conctruction which does indeed produce a 600 ohm characteristic impedance. If it is a line for telephony, then it is a telephone line even if it shares its basic method of construction with telegraph lines, you are making a silly semantic argument here. It's not semantic at all. It's fundamental. You seem to want to walk both sides of the street here, either they are the same, or they are fundamentally different, you can't have it both ways. In any case if you look into the details of the line mentioned on Iain's web page it becomes obvious that the "standard telephone line" he was talking about was not an open wire line such as you are talking about, but was a 19 gauge toll cable. What's a 'toll cable' outside the USA ? Ya got me, you could tell us what they are called in the UK? Are you trying to suggest that this construction is STILL a "standard telephone line" ? I'm not sure if this is a trick question or not, as I expect most new telephone cables, except for those used in the "last mile", are fiber optic cables. But assuming we are talking about copper cables, yes I expect that they still use the same basic construction, the main difference being the use of new and different insulating materials. NO THEY DO NOT USE THE SAME CONSTRUCTION ! OK, I can believe the construction of telephone cables has changed over the years, please describe the changes in the construction of telephone cables over the years, excluding the obvious change in the materials used for insulation? Have you even the tiniest idea what a telegraph line looks like ? Now it is back to open wire lines again, you really seem to have a thing for open wire lines. I don't have the slightest clue how to distinguish a telegraph line from a telephone line, I have always assumed that most of the open wire lines I have seen are telephone lines. I do know that the telephone company also used telegraphic signaling and transmitted telegraph signals over their telephone lines. Also I believe that the telegraph company here in the US leased some of their lines from the telephone company, at least in the latter days. But back to what telegraph lines look like, the only possible distinction I can think of is that telegraph lines may use a different transposition scheme than telephone lines, which use many different transposition schemes depending on the type of carrier system employed with them. Of course the telegraph lines we see in the old "Western movies" are only a single line with an earth return. So why don't you explain what a telegraph line actually looks like and how to distinguish it from a telephone line? What he's getting at and won't tell you even when you ask is that the vintage telegraph line was a single wire with earth return. http://home.iprimus.com.au/oseagram/morse.html Regards, John Byrns |
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