Installs Belden 5301FE for line level?
- Thread starterllewop
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Re: cable type
I think you mean 5301FE. You'll have an extra conductor (do not use it for ground as it is insulated from the shield), I'm not sure about the twist rate and the 18AWG conductors might be a little large for some connectors but there is no specific reason it shouldn't work. Actually, one exception to that would be if plenum cable is required due to the field conditions, that would prohibit using any non-lenum rated cable.
I think you mean 5301FE. You'll have an extra conductor (do not use it for ground as it is insulated from the shield), I'm not sure about the twist rate and the 18AWG conductors might be a little large for some connectors but there is no specific reason it shouldn't work. Actually, one exception to that would be if plenum cable is required due to the field conditions, that would prohibit using any non-lenum rated cable.
Re: cable type
No, that cable isn't appropriate. Audio cable is a twisted pair, and 5301FE is not. Four twists per foot really isn't twisted for electrical purposes. The number of twists per unit length actually affects a balanced system's ability to reject noise pickup. More twists in the pair means better noise rejection.
A balanced input cancels any signal that is equal in amplitude and phase on both conductors. The twisting of the pair helps ensure that noise is induced equally on both conductors. The noise cancellation is called common-mode rejection.
A third, unused conductor could un-balance the noise induction, resulting in more noise in the system, too.
I suggest you buy a box of Belden 9451, which is specifically designed for installed audio runs.
A bit of trivia: Star quad mic cable is simply a fancy way of increasing the amount of twists in the pair without harming the mechanical characteristics of the cable as much. (However it does come at the price of extra capacitance.) The shield of audio cable does a lot less to reject noise than the common-mode rejection of a twisted pair and balanced inputs and outputs/
No, that cable isn't appropriate. Audio cable is a twisted pair, and 5301FE is not. Four twists per foot really isn't twisted for electrical purposes. The number of twists per unit length actually affects a balanced system's ability to reject noise pickup. More twists in the pair means better noise rejection.
A balanced input cancels any signal that is equal in amplitude and phase on both conductors. The twisting of the pair helps ensure that noise is induced equally on both conductors. The noise cancellation is called common-mode rejection.
A third, unused conductor could un-balance the noise induction, resulting in more noise in the system, too.
I suggest you buy a box of Belden 9451, which is specifically designed for installed audio runs.
A bit of trivia: Star quad mic cable is simply a fancy way of increasing the amount of twists in the pair without harming the mechanical characteristics of the cable as much. (However it does come at the price of extra capacitance.) The shield of audio cable does a lot less to reject noise than the common-mode rejection of a twisted pair and balanced inputs and outputs/
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I agree that something like 9451 might be more appropriate and that higher twist rates are better. However, you're talking 4.8 twists per foot versus 6.86 twists per foot, so it is not that it is not that the 5301FE is not twisted, just that it is not as tightly twisted.
I'm not clear on how the third conductor would unbalance anything since it would be unterminated. Twisting works by making the individual conductors more likely to be equally affected by any interference, interfering sources can be directional or physically closer to one side of the cable so by varying the physical relationship of the conductors they are more likely to receive the same interference. A third conductor that is unterminated may limit the twist rate due to simply having more conductors to twist and I could see it increasing SCIN by increasing the variations in distance from the shield, but don't see that it would otherwise significantly affect the resulting CMRR. Am I overlooking something?
Just to clarify, the noise rejection is achieved by the use of a differential input circuit that looks at the difference between the signals on two conductors and thus any signal common to both is rejected. To optimize the noise rejection the concept is to try to make both conductors equally affected by any interference. One major component of this is impedance balancing where both conductors are equal impedance to ground, this is the actual "balanced" aspect and without that a common interference source could result in differences in the signal induced in each conductor. A second major component is twisting, varying the physical relationships of the conductors to try to keep both equally exposed to any interference. Note that the shielding is not really relevant here, as long as any interference affects both conductors equally it will be canceled via the differential input. With such a situation the shielding has minimal impact on the resulting common mode noise rejection, this is one reason that CAT5 and other UTP cabling schemes work so well for analog signals, the tighter twist rates are quite effective when used in conjunction with balanced I/O and differential inputs even though the cable is unshielded.
I'm not clear on how the third conductor would unbalance anything since it would be unterminated. Twisting works by making the individual conductors more likely to be equally affected by any interference, interfering sources can be directional or physically closer to one side of the cable so by varying the physical relationship of the conductors they are more likely to receive the same interference. A third conductor that is unterminated may limit the twist rate due to simply having more conductors to twist and I could see it increasing SCIN by increasing the variations in distance from the shield, but don't see that it would otherwise significantly affect the resulting CMRR. Am I overlooking something?
Just to clarify, the noise rejection is achieved by the use of a differential input circuit that looks at the difference between the signals on two conductors and thus any signal common to both is rejected. To optimize the noise rejection the concept is to try to make both conductors equally affected by any interference. One major component of this is impedance balancing where both conductors are equal impedance to ground, this is the actual "balanced" aspect and without that a common interference source could result in differences in the signal induced in each conductor. A second major component is twisting, varying the physical relationships of the conductors to try to keep both equally exposed to any interference. Note that the shielding is not really relevant here, as long as any interference affects both conductors equally it will be canceled via the differential input. With such a situation the shielding has minimal impact on the resulting common mode noise rejection, this is one reason that CAT5 and other UTP cabling schemes work so well for analog signals, the tighter twist rates are quite effective when used in conjunction with balanced I/O and differential inputs even though the cable is unshielded.
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