Non-Data Applications for Category 5 Cable
Most of this paper was originally presented as "Multimedia with MediaTwist" at Belden "Tech Day",
September 28, 1999
What is Multimedia?
For UTP cable products, "multimedia" is the ability of a cable to support data and non-data applications. Data applications might include 10baseT or 100baseT networking, emerging Gigabit systems, such as Gigabit EthernetTM or WidebandTM .
Non-data applications encompass a wide variety of signal types such as analog audio, in both consumer and professional applications or Video, both analog and digital, and running in applications as diverse as surveillance, factory automation, and professional SDI digital video.
Almost anything done by twisted pairs or coax cables, with bandwidth below approximately 500 MHz is possible. This would therefore include applications such as machine control ( RS-422, or RS-485), or even the bandwidth "king" broadband/CATV
All of these signal types listed above could easily be configured within a network architecture. There are many software packages that allow you to ship audio and video, for instance, as a part of the network data stream. Videoconferencing to the desktop is most often distributed in this fashion. A small video picture of low quality covers a small portion of the user screen. The bandwidth used for the distribution is directly related to the frame rate, the detail, and the size of the image. Often a picture can be displayed for a bandwidth "cost" of only a few kilobits.
Since these network applications are software-driven, cable choice only applies to the network as a whole. And, while we do not intend to discuss these software applications, it should be noted that any application that requires added bandwidth should obviously employ the cable with the widest bandwidth and which provides the greatest possible distance.
What is Shared Sheath?
It's one thing to carry an exotic non-data signal on a UTP cable. But what about using all four pairs of a UTP to handle multiple different signals?
The ability to support more than one signal type on a single 4-pair is termed "shared sheath". It should be mentioned at the outset that shared-sheath applications are mentioned in TIA/EIA 568A but only in regards to multiple data signals on multipair cable, such as 25-pair Category 5. No mention is made of combining non-data applications.
What can be combined in shared sheath? The answer to this question lies squarely in the performance of a UTP cable. Each non-data application has "critical" factors. In multichannel audio, for instance, crosstalk and capacitance are the critical issues. It is then the most critical parameter of the most critical signal that rules over all. This parameter will set things like the "maximum distance" the cable can run.
Some of the shared sheath combinations might include data + data, such as two 10baseT or two 100baseT circuits, data + audio, data + video, multiple audio channels, multiple video channels, audio + video, data + machine control. With each of these combinations, an analysis of the various signals must be made and the requirements of each ascertained.
We are specifically talking about UTP Category cables, including Category 5, and "Enhanced" Category cables, such as Category 5E, and Category "6". There is also data available in the Anixter "Levels" program that may apply to non-data applications. This would include Anixter Level 6 and Level 7 cables. However, in the interest of simplicity, we will concentrate on Category 5 (Belden 7811A), 5e (Belden 1583A and 1700A), and 6 (Belden 1872A).
Plenum versions of the last three cables are also available. Performance of plenum versions, and suitability for non-data applications, is the same as the non-plenum versions mentioned in this paper.
It should be noted that, as of this writing, Category 6 specifications are still not ratified. It is therefore more appropriate to use the performance figures of the actual cable than the standards as outlined in TIA/EIA-568-A and similar documents. Where standards do exist they may be appropriate to judge the performance of "generic" cable for data and non-data applications, but the actual measured performance of a cable will always give more accurate comparisons.
All cables are compared at a distance of 100 meters (328 ft.) Studies done in 1982 by AT&T indicate that this distance covers 99.9% of all network office installations. It is not too hard to imagine, therefore, than the same distance would be appropriate for most non-data installations. One exception to this might be factory automation and control.
Unbalanced Analog Audio Requirements
Unbalanced audio is the "standard" for consumer audio interconnection. Since Category products are now commonly used in the wiring of new houses, and home communication upgrades, it is essential that we include it here. However, these cables have no standards, just "common" standards...
Parameter 7811A Unbalanced analog Crosstalk -102 dB @ 20 kHz -90 dB @ 20 kHz Impedance 100 ± 15 No requirements Capacitance 15 pF/ft <50 pF/ft. Gage 24 AWG No requirements Format Balanced Unbalanced Distance 100 meters (328 ft.) 20-30 ft. maximum
Since this is an unbalanced standard, in order to employ UTP, or any twisted pairs, a balun must be used. The choice of baluns is covered in a later section.
Balanced Analog Audio Requirements
Balanced analog audio cables are stranded twisted pairs of 22AWG or 24AWG, with a foil shield and drain wire, and covered with an overall jacket. They are commonly used in professional installations such as radio or television stations, or recording studios.
Parameter 7811A 1583A/1700A 1872A Balanced Audio Crosstalk
at 20 kHz
-102 dB -105 dB Unreadable
used to be -60 dB
now, it's -90 dB
at 20 kHz
-102 dB -105 dB Unreadable
used to be -60 dB
now, it's -90 dB
Impedance 100 ± 15 100 ± 12 100 ± 12 No requirements Capacitance 15 pF/ft 15 pF/ft 15 pF/ft 30 -- 50 pF/ft. Gage 24 AWG 24 AWG 24 AWG 22 AWG/24 AWG Format Balanced Balanced Balanced Balanced Conductor Solid Solid Solid Stranded Construction UTP UTP UTP Foil shield
Another View of UTP and Balanced Lines
One manufacturer, Radio Systems (Dan Braverman, Michael Sirkis), has brought out a series of products called "Studio Hub". These are balanced line analog audio patch panels which use Category 5 as the wiring medium. However, they suggest shielded Category 5 (STP). The decision to use STP rather than UTP was based on the requirement for good common mode noise rejection (CMRR). The following quote is from an email of Mr. Sirkis:
"Radio Systems has no control over what signals will be connected to Studio Hub. This means balanced or unbalanced (although we say StudioHub is a balanced product someone will either hook up an unbalanced piece of equipment or unknowingly create an unbalanced connection), and any signal level from mic to line. We also have no control on what signals maybe adjacent to Studio Hub cables.
In addition, most broadcast equipment is designed with active differential inputs that are constructed with 1% resistors. There is no trimming provided for CMRR. Hence, 40 dB CMRR is often the case (or worse if all the resistor values go to the wrong side of the tolerance). Sometimes, station engineers will build circuits with what ever parts are available -- 5% resistors (now its 26 dB CMRR).
While there is some tolerance (from the user) for cross talk between left and right channels (of the same source) there is no tolerance for cross talk between dissimilar signals. Since we can't count on the rejection of common mode signals, or masking them with level the best thing to do about crosstalk is to minimize it from happening. Hence, shielded cable."
Also, during initial development of StudioHub not a single customer was willing to consider StudioHub with UTP. Without STP there would have been very little (if any) StudioHub sold.
The lessons here are obvious. For any data or non-data application, the performance of the cable is only as good as the boxes to which it is attached. You can ruin excellent cable performance with poor equipment choices.
However, this problem is not insurmountable if one chooses to determine the CMRR figures of equipment before it is purchased. Most modern analog equipment provides excellent performance values.
Stop Thinking in a "Shielded World"
It is fully understood that many engineers, especially those in broadcast, were raised in a "shielded pair" world, and the idea of using UTP requires a philosophical jump. But isn't that why you're reading this paper? You want to be given all the options before you decide how to wire up an installation. UTP is definitely one of those options!
Note: For UTP to be effective in most audio systems, the radiating signal must be extremely low and the CMRR high. This requires the source differential output to be equal and opposite (equal symmetry). In addition, the destination differential amplifier must have excellent CMRR. This is not commonplace in today's environment and therefore careful consideration must be used in designing such a system. The effects of low frequency shielding and coupling can not simply be ignored without the proper considerations.
There are many other benefits to UTP, such as no ground loops (no shield, no drain wire) which would be attractive to designers of non-data systems.
What is a Balanced Line?
A balanced line is a wiring configuration that uses two wires to transfer the signal from point to point. The key is that the signal is the same on both wires, but opposite polarity (see arrows). Thus, if you add up the signal at any given place along the pair, the sum total should always be zero.
Signals travel in opposite direction or "differential mode".
When noise strikes the pair, it induces a voltage in the same ("common mode ") direction. At either end of the cable is a transformer or active balanced circuit (and electronic equivalent to a transformer). Since this will only pass signals that are of opposite polarity ("differential mode"), the noise, which is the same, cancels out.
Noise travels in the same direction or "common mode"
The construction of the cable and the "balance" of the system at either end are critical for good noise rejection. In multipair cables, this is also the basis for low crosstalk. Here is a list of factors that will compromise low noise and low crosstalk performance:
- The conductors are not the same size (AWG) or same resistance. ("Resistance unbalance")
- The conductors are not the same length. ("Resistance unbalance")
- The conductors are not in the center of their insulation. ("Capacitance unbalance")
- The conductors vary in distance between them ("Capacitance unbalance")
- The different pair twistings are not ideal.
- Bending the cable forces pairs together ("nesting") which dramatically increases crosstalk.
- Bending the cable makes pairs separate, changing the impedance of that pair, making them radiate signal energy.
Here's why fixing these problems leads to lower crosstalk and lower noise ingress/egress:
The closer the wires are to each other, the more identical the noise is on both wires and the more completely it cancels out.
There is currently no computer on earth that could cost-effectively determine the most effective twist ratios between four pairs at 100 MHz (much less 350 MHz or 550 MHz).
Dramatically different twist ratios can give you excellent crosstalk numbers. But the length of the wires is also radically different, affecting skew/delay, the timing of the four pairs. Skew/delay is critical in systems that use all four pairs simultaneously such as Gigabit network protocols or RGBS video transmission.
Separating the pairs physically dramatically improves crosstalk. But the construction must keep the pairs separated, especially when the cable is flexed or bent.
Digital Audio Requirements
Digital audio is a sampled version of analog audio. Desired quality is achieved by choosing different sampling rates. The higher the sampling rate, the better the copy will be at the end of the process. Here are the sampling rates and bandwidths:
Sampling Rate Multiply by... Bandwidth Application 32 kHz 128 4.096 MHz Voice/News 38 kHz 128 4.864 MHz DAT 44.1 kHz 128 5.6448 MHz Home CD 48 kHz 128 6.144 MHz Audio w/Video 96 kHz 128 12.288 MHz Recording 192 kHz 128 24.576 MHz Recording
In any system with multiple bandwidths, "If it works with the highest, it will work with them all." So, we compare AES/EBU digital audio requirements at 25 MHz, the highest bandwidth.
On the next page, we compare digital audio with standard Category 5. This is such a good fit, that many people are surprised. They shouldn't be! Digital audio is really just another type of data stream, a rather generic one at that, built to run down high quality twisted pairs.
Parameter 7811A AES/EBU Digital Audio Crosstalk -41 dB @ 25 MHz -30 dB @ 25 MHz Impedance 100 ± 15 110 ± 20% (88-132) Capacitance 15 pF/ft 13 pF/ft. Gage 24 AWG 22/24 AWG, no spec Format Balanced Balanced Conductor Solid Stranded Construction UTP Shielded
All UTP constructions do well with AES/EBU digital.
Parameter 7811A 1583A/1700A 1872A AES/EBU Audio Crosstalk @ 25 MHz -41 dB -44.3 dB -51.3 dB -30 dB Impedance 100 ± 15 100 ± 12 100 ± 12 110 ± 20% Capacitance 15 pF/ft 15 pF/ft 15 pF/ft 13 pF/ft Gage 24 AWG 24 AWG 24 AWG 22/24 AWG Format Balanced Balanced Balanced Balanced Conductor Solid Solid Solid Stranded Construction UTP UTP UTP Foil shield
There are three standards for AES/EBU. The first is the balanced line, outlined above. The other two are based on coax cable. There is a professional version (AES-3id) and a consumer version (S/PDIF). They are not identical and not completely compatible. To use twisted pairs in the coax version, a balun would be required to convert from 110 twisted pairs to 75 coax.
Parameter 7811A 1583A/1700A 1872A Standard analog video Bandwidth 100 MHz 200 MHz 350 MHz DC to 4.2 MHz Crosstalk -53 dB @ 4 MHz -56 dB @ 4 MHz -63 dB @ 4 MHZ -60 dB (no spec) Impedance 100 ± 15 100 ± 12 100 ± 12 75 ± 3 Capacitance 15 pf/ft 15 pf/ft 15 pf/ft 20 pF/ft. Gage 24 AWG 24 AWG 24 AWG Varies with cable size Format Balanced Balanced Balanced Unbalanced
Since standard video cable is "unbalanced" coax, it is not directly compatible with any twisted pair or UTP format. To use UTP, we must convert from BALanced to UNbalanced. The device is therefore called a BALUN. (That's "bal-un", not "bay-lun"). Baluns are sometimes called "matching transformers" or "impedance converters."
Digital video comes in a number of data rates. Here are some of the uncompressed professional video formats:
Data Rate Bandwidth Protocol 143 Mbps 71.5 MHz NTSC composite 177 Mbps 88.5 MHz PAL composite 270 Mbps 135 MHz NTSC/PAL component
All of these appear in the standard SMPTE 259M. The most common is the 270-Megabit standard, and therefore all cable and system testing are done to that standard. It should be noted that 135 MHz is beyond the 100 MHz limit for standard Category 5. Therefore, this cable is eliminated from running these signals and Category 5e or 6 cables are then required.
Significant live testing was done with 270/135 at UL Labs. Both bonded-pair Belden products (1700A, 1872A) passed the Class A -- Digital Devices spec for digital coax to the home. These are the first, and so far only, twisted pair cables to have passed this test.
Below are the comparisons between SMPTE 259M SDI (serial digital interface) and Category 5e and Category 6. It is obvious that a balun will be required to match the impedance and to convert from balanced to unbalanced (and back again).
Parameter 7811A 1583A/1700A 1872A SMPTE 259M Bandwidth 100 MHz 200 MHz 200 MHz 135 MHz Crosstalk @ 135 MHz Unknown >33 dB >40 dB -30 dB Impedance 100 ± 15 100 ± 12 100 ± 12 75 ± 3 Capacitance 15 pF/ft 15 pF/ft 15 pF/ft 16 pF/ft Gage 24 AWG 24 AWG 24 AWG Coax - various Format Balanced Balanced Balanced Unbalanced Conductor Solid Solid Solid Solid center Construction UTP UTP UTP Coax Distance Not Useable 328 ft. 450 ft. >659 ft.
It should be noted that coax cable would go significantly farther than UTP, based on superior impedance tolerance and lower resistance (more copper).
Machine Control Requirements
Machine control systems are basically low data rate networks for controlling devices. In the broadcast world, they are commonly used to control audio and video tape machines, cart playback devices, or hard disc servers, which mimic tape machines.
Hard-disc servers are becoming the de facto standard to replace audio and video tape machines and are the first widely accepted amalgam of data and audio/video technology. So audio, video, and control signals to this equipment could employ the same cable. The table below compares Category 5 to the three common forms of machine control.
Parameter 7811A RS-232 RS-422 RS-485 Bandwidth 100 MHz Unspecified 10 MHz 10 MHz Crosstalk 47 dB @ 10 MHz Unspecified Unspecified Unspecified Impedance 100 ± 15 Unspecified 100 120 Capacitance 15 pF/ft 30 pF/ft 12.5 pF/ft 12.5 pF/ft Gage 24 AWG Unspecified 24 AWG 24 AWG Format Balanced Unbalanced* Balanced Balanced Construction UTP Stranded Stranded Stranded
*We are unaware of any baluns made to convert RS-232 to UTP.
The hardest of all non-data applications for UTP is broadband/CATV because of one single factor, bandwidth. Cable TV systems often go up to 1 GHz (158 channels) or more. There are even 500-channel systems currently being offered.
Since Category 5 is only specified to 100 MHz (and even MediaTwist is only spec'd to 550 MHz), these UTP cables offer insufficient parameters to carry the full spectrum of broadband/CATV signals. Does this mean you can't use UTP for broadband/CATV? No. It just means you will be bandwidth (channel) limited.
There are many applications, such as schools, hotels and hospitals, where only a few channels are offered. In those applications, UTP might be a possible choice.
The other limitation to UTP is gage size. Two 24 AWG wires do not come close to a broadband/CATV cable in terms of basic resistance. Therefore, UTP is significantly limited in distance compared to standard coax designs.
And finally, we have cost. Broadband/CATV coax is very cost-effective. Its cost is probably closer to Cat 5 than any other application we have mentioned so far.
Therefore, UTP really offers only one thing which coax cannot: versatility. Installed in a hotel, for instance, UTP can deliver any one of a dozen types of signals. It can be 100baseT for one customer, deliver video for the next, be an Internet access port the next day, all while running automated devices in the room.
Many of these applications can be running on different pairs inside the same cable, "shared sheath", which we touch on below. This table is the comparison with broadband /CATV:
Parameter 7811A 1583A/1700A 1872A CATV (RG-6) Attenuation 22 dB @100 MHz 32 dB @200 MHz 40 dB @350 MHz 12 dB @350 MHz Bandwidth 100 MHz 200 MHz 350 MHz 1 GHz+ Equiv. Channel Channel 6 Channel 22 Channel 45 Channel 158+ Impedance 100 ± 15 100 ± 12 100 ± 12 75 Capacitance 15 pF/ft 15 pF/ft 15 pF/ft Unspecified Gage 24 AWG 24 AWG 24 AWG Different/CCS Format Balanced Balanced Balanced Unbalanced Conductor Solid Solid Solid Solid CCS Construction UTP UTP UTP Coax
Since broadband/CATV is an unbalanced system a balun is required to run those signals on UTP. It should be noted that not only the cable, but also the balun will be required to handle an extremely wide bandwidth since even standard CATV goes up to 1 GHz . With Belden MediaTwist, we give some specs out to 550 MHz, equivalent to Cable Channel 78. The widest bandwidth balun available is the ETS PV-884, which is specified out to 850 MHz. (Channel 121.)
Comparison of Attenuation between UTP and broadband/CATV RG-6 at 100 meters
Cable 50 MHz 100 MHz 200 MHz 350 MHz RG-6 4.66 dB 9.16 dB 11.9 dB Category 5 16 dB 22 dB No data to compare Category 5e 15.8 dB 21.7 dB 32 dB No data Category 6 15.5 dB 19.9 dB 29.1 dB 40 dB
As you can see, there's really no comparison. UTP cannot go as far as coax, cannot handle as broad a bandwidth as coax. The key advantage to UTP is versatility. Broadband/CATV coax will only be that: coax into your television. It will never connect to your phone, or run an automated factory, or even carry audio. But multimedia cables, such as MediaTwist, can easily do that and more.
Shared Sheath Requirements
Shared sheath systems are driven by the "critical signal". This is often the cable with the highest frequency, or possibly the widest bandwidth. The pair with that signal will be the controlling factor for the entire cable.
Since the parameters for all different signals are so varied, it is virtually impossible to predict how multiple signals will interact. But the chart below is a starting point:
Shared-Sheath Critical Parameters
A = attenuation
B = bandwidth
C = capacitance
I = impedance/impedance tolerance
X = crosstalk
Unbalanced Audio Balanced Audio Digital audio Standard Video Digital SDI Video RS-422 RS-485 10baseT 100baseT Unbalanced Audio C,X C, X X A,I B, A, I X, C X X X Balanced Audio C,X C, X X A,I B, A, I X, C X X X Digital audio X X A, I X B,A, I I I I X, I Standard Video A, I A, I X A, I B, A, I A, I A, I A, I, X A, I, X Digital SDI Video B, A, I B, A, I B, A. I B,A,I B, A, I B, A, I B, A, I B, A, I B, A, I, X RS-422 X, C X, C I A, I B, A, I X X X X RS-485 X X I A, I B, A, I X X X X 10baseT X X I A, I, X B, A, I X X X X 100baseT X X X, I A, I, X B, A, I, X X X X X
You will note that crosstalk is by far the most common critical factor. As frequencies go higher, impedance, bandwidth and attenuation come into play. Capacitance is a critical factor only with audio, but because Category cables are so good, with such low capacitance, capacitance becomes a non-issue with most other signal types.
And, if you intend to do some shared sheath applications, here's where you can start. Fill in the blanks below with the parameters for the signals you intend to feed down the pairs. You have two blanks below, but that could be duplicated to give you four. We have inserted Category 5 specifications, but if you use cable which is 5e or 6, make your own chart and start with those!
Parameter Category 5 Crosstalk @ MHz Impedance 100 ± 15 Capacitance 15 pF/ft Gage 24 AWG Format Balanced
Where Shared Sheath Fails
Shared-sheath applications fail where UTP itself fails. The limitations are based on the resistance of 24 AWG pairs. This is obviously why these cables cannot be used for power conductors or speaker cables. These and other similar applications require low resistance.
The second limitation is bandwidth. Where low-loss at high frequencies are required, coaxial cable is still the "king". But UTP, especially enhanced UTP is encroaching on this realm of "coax" and is getting closer all the time. This is one of the reasons that uncompressed broadcast quality HD-SDI signals are not even mentioned. They run at a bandwidth of 750 MHz, for which no data is available on any UTP. And, even if the UTP were perfect, the 24 AWG resistance would limit HD-SDI signals to about 90 feet.
Are we done playing with twisted pairs? Absolutely not! Maybe the "next" super UTP will be able to carry broadband/CATV to 500 channels, or uncompressed HD-SDI, or microwave signals!
If our investigation into twisted pairs has proven anything, it is that this transmission medium is far from dead!
Other New Systems
There are new networking systems emerging such IEEE 1394 "FirewireTM ". This is a hot-swap "hubless" network scheme mainly for consumers, but it may have limited professional applications as well. While the standard cable looks nothing like Category 5, the IEEE Committee is currently considering Category 5 as an alternate wiring method.
Since the cable carries signals and power, the limitation to distance is based on resistance of 24 AWG UTP. Even then, it is felt that the distance currently specified between devices (4.5m, or 15 ft.) could be increased up to (45m or 150 ft.) with Category 5. The trick may be to double-up the conductors used to carry power, thus cutting the resistance in half.
So What Do I Need to Run...
Application Balun? ETS Part # Comments 10baseT No 100baseT No Gigabit EthernetTM No No shared sheath WidebandTM No No shared sheath Analog Consumer Audio Yes PA-800 series Analog Balanced Audio No Forced balancing option Digital Audio (balanced) No Forced balancing option Digital Audio (coax) Yes PA-810 series XLR to BNC Analog video Yes PV-860 series Bandwidth 4.5 MHz Analog video Yes PV-840 Bandwidth 60 MHz RGB-S Yes PV-890 series BNC or HD-9 S-Video* plus stereo audio Yes PV-902 consumer unbalanced Audio + Video (baseband) Yes PV-900 consumer = RCA jacks Digital video Yes PV-850 (270Mbps/135 MHz) Broadband/CATV Yes PV-882 series Cable Channel 77 Broadband/CATV Yes PV-884 series Cable Channel 121
* Also known as Y/C or S-VHSTM. VHS is a trademark of JVC. Ethernet is a trademark of Xerox Corp. Wideband is a trademark of Wideband Corp.
Thanks to ETS (Energy Transformation Systems) for their work on UTP baluns. They can be reached at www.etslan.com, 1-800-752-8208
And it's not just ETS...
There are many other balun manufacturers. Many of them can be found on Belden's web page in the white paper "Video and UTP". You can find it at www.belden.com/Video and UTP.pdf.
We're Interested Too!
Are you planning an installation of UTP for a non-data application not mentioned in this paper? The author would be very interested in talking to you. If you have any questions or comments on the contents of this paper, contact the author at Steve.Lampen@belden.com.