I know we have talked a lot about shielded cable here and what some of you have used.
What is the difference between say, the small diameter (20 gauge) Teflon shielded cable like Apex Jr. sells and the various RG cables like RG 174.
Can you use the 50 or 75 ohm coax cable in an amp?
What is different about audio and the RG coax cables?
Thanks
Shielded Cable
Moderators: pompeiisneaks, Colossal
Shielded Cable
Tom
Don't let that smoke out!
Don't let that smoke out!
Re: Shielded Cable
Tom, in our application the circuit impedance is such a great mismatch with the very low cable impedence that there is no tangible difference between 50 & 75 cables. However, physically most 75 ohm cables tend to be larger and with a stiffer dielectric thus may not be practical for the types of wire runs inside of an small enclosure.
In contrary is RG735A, which is a small O.D. 75 ohm cable and a fav of mine. At only about 18pf/ft it works well for input shielding, but may not be the best application in other areas of the circuit if you need some added capacitance to color the tone.
Radio Grade Cables : http://en.wikipedia.org/wiki/Coax
FYI, Wiki is wrong, RG stands for Radio Grade, not Radio Guide as stated.
Balanced Audio cables : http://en.wikipedia.org/wiki/Balanced_audio
TM
In contrary is RG735A, which is a small O.D. 75 ohm cable and a fav of mine. At only about 18pf/ft it works well for input shielding, but may not be the best application in other areas of the circuit if you need some added capacitance to color the tone.
Radio Grade Cables : http://en.wikipedia.org/wiki/Coax
FYI, Wiki is wrong, RG stands for Radio Grade, not Radio Guide as stated.
Balanced Audio cables : http://en.wikipedia.org/wiki/Balanced_audio
TM
Re: Shielded Cable
THanks TM.
I was trying to figure out if using say a 50 ohm coax is not good to use inside an audio amp but from what I'm reading the runs are so short inside an amp it doesn't really affect anything other than the capacitance of the cable.
Coax cable is made to a certain impedance so that high frequency radio waves are not reflected back to the device and acts as a continuation of that device to its destination.
I was trying to figure out if using say a 50 ohm coax is not good to use inside an audio amp but from what I'm reading the runs are so short inside an amp it doesn't really affect anything other than the capacitance of the cable.
Coax cable is made to a certain impedance so that high frequency radio waves are not reflected back to the device and acts as a continuation of that device to its destination.
Tom
Don't let that smoke out!
Don't let that smoke out!
Re: Shielded Cable
It seems my 124 amp is very responsive to the type and length of cable patched through the in/out jacks in terms of controlling the high end. I would not be surprised at all if the white cables in 124 were some 'junk' cables the significantly shape the tone of that amp for the better.
Re: Shielded Cable
because most coax is made with a ferrous core, u might be careful using it for audio circuits, it can pick up hum. shielded audio cable is a better bet--
Re: Shielded Cable
Coaxial cable are typically characterized with the impedance and cable loss. The length has nothing to do with a coaxial cable impedance. Characteristic impedance is determined by the size and spacing of the conductors and the type of dielectric used between them. For ordinary coaxial cable used at reasonable frequency, the characteristic impedance depends on the dimensions of the inner and outer conductors. The characteristic impedance of a cable (Zo) is determined by the formula 138 log b/a, where b represents the inside diameter of the outer conductor (read: shield or braid), and a represents the outside diameter of the inner conductor.
Here is a quick overview of common coaxial cable impedances and their main uses:
50 ohms: 50 ohms coaxial cable is very widely used with radio transmitter applications. It is used here because it matches nicely to many common transmitter antenna types, can quite easily handle high transmitter power and is traditionally used in this type of applications (transmitters are generally matched to 50 ohms impedance). In addition to this 50 ohm coaxial cable can be found on coaxial Ethernet networks, electronics laboratory interconnection (foe example high frequency oscilloscope probe cables) and high frequency digital applications (fe example ECL and PECL logic matches nicely to 50 ohms cable). Commonly used 50 Ohm constructions include RG-8 and RG-58.
60 Ohms: Europe chose 60 ohms for radio applications around 1950s. It was used in both transmitting applications and antenna networks. The use of this cable has been pretty much phased out, and nowdays RF system in Europe use either 50 ohms or 75 ohms cable depending on the application.
75 ohms: The characteristic impedance 75 ohms is an international standard, based on optimizing the design of long distance coaxial cables. 75 ohms video cable is the coaxial cable type widely used in video, audio and telecommunications applications. Generally all baseband video applications that use coaxial cable (both analogue and digital) are matched for 75 ohm impedance cable. Also RF video signal systems like antenna signal distribution networks in houses and cable TV systems are built from 75 ohms coaxial cable (those applications use very low loss cable types). In audio world digital audio (S/PDIF and coaxial AES/EBU) uses 75 ohms coaxial cable, as well as radio receiver connections at home and in car. In addition to this some telecom applications (for example some E1 links) use 75 ohms coaxial cable. 75 Ohms is the telecommunications standard, because in a dielectric filled line, somewhere around 77 Ohms gives the lowest loss. For 75 Ohm use common cables are RG-6, RG-11 and RG-59.
93 Ohms: This is not much used nowadays. 93 ohms was once used for short runs such as the connection between computers and their monitors because of low capacitance per foot which would reduce the loading on circuits and allow longer cable runs. In addition thsi was used in some digital commication systems (IBM 3270 terminal networks) and some early LAN systems.
Sometimes coaxial cables are used also for carrying low frequency signals, like audio signals or measurement device signals. In audio applications especially the coaxial cable impedance does not matter much (it is a high frequency property of cable). Generally coaxial has a certain amount of capacitance (50 pF/foot is typical) and a certain amount of inductance. But it has very little resistance.
General characteristics of cables:
A typical 50 ohm coax coaxial cable is pretty much 30pf per foot (doesn't apply to miniature cables or big transmitter cables, check a cable catalogue for more details).
A typical 75 ohm coaxial cable is about 20 pf per foot (doesn't apply to miniature cables or big transmitter cables, check a cable catalogue for more details). 7
A typical 93 ohm is around 13 pf per foot (does not apply to special cables). This cable type is ued for some special applications.
Please note that these are general statements. A specific 75 ohm cable could be 20pF/ft. Another 75 ohm cable could be 16pF/ft. There is no exact correlation between characteristic impedance and capacitance.
Tony
Here is a quick overview of common coaxial cable impedances and their main uses:
50 ohms: 50 ohms coaxial cable is very widely used with radio transmitter applications. It is used here because it matches nicely to many common transmitter antenna types, can quite easily handle high transmitter power and is traditionally used in this type of applications (transmitters are generally matched to 50 ohms impedance). In addition to this 50 ohm coaxial cable can be found on coaxial Ethernet networks, electronics laboratory interconnection (foe example high frequency oscilloscope probe cables) and high frequency digital applications (fe example ECL and PECL logic matches nicely to 50 ohms cable). Commonly used 50 Ohm constructions include RG-8 and RG-58.
60 Ohms: Europe chose 60 ohms for radio applications around 1950s. It was used in both transmitting applications and antenna networks. The use of this cable has been pretty much phased out, and nowdays RF system in Europe use either 50 ohms or 75 ohms cable depending on the application.
75 ohms: The characteristic impedance 75 ohms is an international standard, based on optimizing the design of long distance coaxial cables. 75 ohms video cable is the coaxial cable type widely used in video, audio and telecommunications applications. Generally all baseband video applications that use coaxial cable (both analogue and digital) are matched for 75 ohm impedance cable. Also RF video signal systems like antenna signal distribution networks in houses and cable TV systems are built from 75 ohms coaxial cable (those applications use very low loss cable types). In audio world digital audio (S/PDIF and coaxial AES/EBU) uses 75 ohms coaxial cable, as well as radio receiver connections at home and in car. In addition to this some telecom applications (for example some E1 links) use 75 ohms coaxial cable. 75 Ohms is the telecommunications standard, because in a dielectric filled line, somewhere around 77 Ohms gives the lowest loss. For 75 Ohm use common cables are RG-6, RG-11 and RG-59.
93 Ohms: This is not much used nowadays. 93 ohms was once used for short runs such as the connection between computers and their monitors because of low capacitance per foot which would reduce the loading on circuits and allow longer cable runs. In addition thsi was used in some digital commication systems (IBM 3270 terminal networks) and some early LAN systems.
Sometimes coaxial cables are used also for carrying low frequency signals, like audio signals or measurement device signals. In audio applications especially the coaxial cable impedance does not matter much (it is a high frequency property of cable). Generally coaxial has a certain amount of capacitance (50 pF/foot is typical) and a certain amount of inductance. But it has very little resistance.
General characteristics of cables:
A typical 50 ohm coax coaxial cable is pretty much 30pf per foot (doesn't apply to miniature cables or big transmitter cables, check a cable catalogue for more details).
A typical 75 ohm coaxial cable is about 20 pf per foot (doesn't apply to miniature cables or big transmitter cables, check a cable catalogue for more details). 7
A typical 93 ohm is around 13 pf per foot (does not apply to special cables). This cable type is ued for some special applications.
Please note that these are general statements. A specific 75 ohm cable could be 20pF/ft. Another 75 ohm cable could be 16pF/ft. There is no exact correlation between characteristic impedance and capacitance.
Tony
" The psychics on my bench is the same as Dumble'"
Re: Shielded Cable
http://www.generalcable.com/NR/rdonlyre ... lGuide.pdf
http://www.generalcable.com/NR/rdonlyre ... bl_TOC.pdf
My wife's company sells all types of wire so I have been looking at her Carrol wire/general cable catalog and the warehouse wire reels.
The telecommunications sales person at your local wire or electrical wholesale company can help out. Which you can purchase at the city desk of your local company.
Most are black, some biege and some white.
Mark
http://www.generalcable.com/NR/rdonlyre ... bl_TOC.pdf
My wife's company sells all types of wire so I have been looking at her Carrol wire/general cable catalog and the warehouse wire reels.
The telecommunications sales person at your local wire or electrical wholesale company can help out. Which you can purchase at the city desk of your local company.
Most are black, some biege and some white.
Mark
Re: Shielded Cable
Actually. the origin of 50,60 and 75 ohm coaxial cable is a lot less complicated than that......
A singel dipole antenna has a teoretical impedance of 72 ohms......
The bandwidth of a dipole antenna ( the range of freq. with an acceptable impedance, or rather SWR) is set with the d/l ratio , diameter over length. One way to increase the apparent diameter of a dipole section, be it a single dipole or the active element of your typical yagi TV antenna, is to make a folded dipole. Unfortunately this also acts as a 1:4 transformer and increases the impedance to appx 300 ohms - but the dipole is a balanced element, and up through the 70s, we had balanced cable feeds, also called flat cable, which is tricky to work with, as it needs to be supended off grounded surfaces. By adding the parasitic elements used on a Yagi type antenna, the impedance can be lowered to around 240 ohms - now enter the 4:1 balun ( balanced to unbalanced) transformer - and voilá - there's your 60 ohm cable.....or one can tune the Yagi impedance closer to 300 ohms, and again use the 4:1 balun found inside most TV yagis.....
50 ohms was selected as a compromise for transmitters, matching the actual transmitter impedance to something practical......thus most lab grade coaxial cable is now 50 ohms. The 4:1 300:75 ohm is the reason for choosing 75 ohms for cable distribution of radio and TV, as these are all receiving elements. 75 ohm cables usually also has a little lower capacitance than 50 ohms, as the ratio of diameters of inner/outer conductor as larger, - this also which sets the cables impedance together with the dielectric properties of the inner insulation.
For audio use, the impedance bears absolutely no relevance, - capacitance pr. foot ( or meter
) is another story....
A singel dipole antenna has a teoretical impedance of 72 ohms......
The bandwidth of a dipole antenna ( the range of freq. with an acceptable impedance, or rather SWR) is set with the d/l ratio , diameter over length. One way to increase the apparent diameter of a dipole section, be it a single dipole or the active element of your typical yagi TV antenna, is to make a folded dipole. Unfortunately this also acts as a 1:4 transformer and increases the impedance to appx 300 ohms - but the dipole is a balanced element, and up through the 70s, we had balanced cable feeds, also called flat cable, which is tricky to work with, as it needs to be supended off grounded surfaces. By adding the parasitic elements used on a Yagi type antenna, the impedance can be lowered to around 240 ohms - now enter the 4:1 balun ( balanced to unbalanced) transformer - and voilá - there's your 60 ohm cable.....or one can tune the Yagi impedance closer to 300 ohms, and again use the 4:1 balun found inside most TV yagis.....
50 ohms was selected as a compromise for transmitters, matching the actual transmitter impedance to something practical......thus most lab grade coaxial cable is now 50 ohms. The 4:1 300:75 ohm is the reason for choosing 75 ohms for cable distribution of radio and TV, as these are all receiving elements. 75 ohm cables usually also has a little lower capacitance than 50 ohms, as the ratio of diameters of inner/outer conductor as larger, - this also which sets the cables impedance together with the dielectric properties of the inner insulation.
For audio use, the impedance bears absolutely no relevance, - capacitance pr. foot ( or meter
) is another story....Re: Shielded Cable
Where did you get this information?butwhatif wrote:because most coax is made with a ferrous core, u might be careful using it for audio circuits, it can pick up hum. shielded audio cable is a better bet--
Good quality coax (MIL grade) is made w/ non-ferrous metals or alloys such as copper or silver coated copper. I know of no such cables using ferrous metals such as iron or steel. They are poor conductors compared to Silver or Copper. Even lower grade coax uses Aluminum, also a non-ferrous metal. Coax cable by nature is a shielded cable, however the braid or foiled braid depends on the amount of shielding such as 80%, 100%, etc.
Here's a simple test to try... if a magnet sticks to the center core, then it's ferrous, if not, it's non-ferrous.
Re: Shielded Cable
God point, Bob... I actually forgot to comment on the ferrous coax..
which is non-existent! Any ferrous content will muck up the impedance calc's as the permeabilty factor is always set to 1 - i.e. no ferrous content!
which is non-existent! Any ferrous content will muck up the impedance calc's as the permeabilty factor is always set to 1 - i.e. no ferrous content!
Re: Shielded Cable
I have seen rg-162u, rg-58u and rg-62u that were ferrous. for that reason i never use it in amps. i have removed 162u from amps where it was inducing hum. always use a strong magnet on it to test if u r unsure. i was quite surprised to find that out.
Re: Shielded Cable
Right now I am running RG174/u 93.0 ohm/ft, nominal capacitance 30.80/ft, and nominal impedence 50 ohms. It is only 26 awg. Braid shield is 10.3 ohm/ft.
So will up that to RG58/u 19 awg 8.1 ohm/ft this in white PVC jacket. Braid shield is 2.9 ohm/ft. RG6 is larger jacket diameter with better resistance on longer runs.
Looking at some twin axial cables UL CL2 20 ga. as well.
Mark
So will up that to RG58/u 19 awg 8.1 ohm/ft this in white PVC jacket. Braid shield is 2.9 ohm/ft. RG6 is larger jacket diameter with better resistance on longer runs.
Looking at some twin axial cables UL CL2 20 ga. as well.
Mark