# Tag Info

36

Coax was used for its controlled impedance, its bandwidth and its self-shielding properties. Sure, twisted-pair wiring has existed for a very long time, mostly used to carry audio frequencies in telephone wiring. That isn't where the technical advancement was required. In order to compensate for twisted-pair's lossiness and impedance issues, major ...

19

A even number of twists is better, but I am not aware of practical cable situations where this is worth the trouble: there are other sources of interference which are probably more important that the small difference it would make. Another way to look at it: the amount of magnetic interference is proportional to the area between the two wires. With a ...

17

Unshielded twisted pair (CAT1 and CAT2 Phone cables) at the time (early '80) did not have enough performance, and coax (10Base2, 10Base5) did not require hubs (which were quite expensive then). When 10BaseT was ratified (CAT3), the price of hubs (and switches afterwards) went down due to mass production.

14

The problem is not with the cabling. The problem is with the relative cost of electronics versus cabling. Twisted pair existed at that time, as it had been used for phone lines for a long time. However, the idea of having a separate piece of hardware doing switching in the middle, using the star topology used today for twisted pair, would add cost and ...

13

Do some time domain reflectometry, a useful video to this process is probably one from w2aew. He shows it with a coax, but it should work with anything that has a somewhat consistent impedance. In short: Inject a pulse with a short risetime into the cable terminate the cable with a potentiometer that has the range of suspected impedance (like 200Ω) Watch ...

11

The an even or odd number of twists is for all intents and purposes arbitrary. What is more important is the number of Twists per Inch (TPI). The higher this number, the more that noise cancellation will be achieved. Why? well simply put any noise sources (magnetic fields, etc.) will usually vary over the length of the cable. If you can twist a cable more ...

10

From a professional point of view, this is a critical problem. Missing termination will cause energy bouncing back at the end which isn't terminated. This could lead to strange random noise on the line, such as for example transients or random pulses that seem like ok binary pulses, but with wrong voltage levels etc. CAN Hi and Lo don't necessarily behave ...

8

Scheme #1 is terminating only the differential mode signal, not the common mode. Scheme #2 is terminating both differential and common mode. Even with a perfectly symmetrical differential output signal you will have what we call "differential to common mode conversion" in the cable. So at the receiver you will have both common mode and differential mode. ...

8

A CAT5 cable has 4 twisted pairs. You will want to use 1 pair of wires per phone line. The standard arrangement is the blue pair is the first phone line. Assuming the wiring your connecting to is the standard Green/Red/Yellow/Black used in the US, and that it's connected correctly, connect the existing Red wire to the Blue with White wire, and Green to the ...

7

Twisting the wires exiting a high frequency wound component (that might be carrying several amps) is a way of reducing the electromagnetic interference generated to other parts of a circuit.

7

The LVDS are differentially terminated (across phases) so there should be no net flow of current - it is balanced. The twisted pairs give you quasi TEM mode propagation so the concern of the shield here is purely electric field. terminate at one end as you have drawn to avoid introducing current loops. Since you have implemented a differential CAN system ...

7

OK so the key is in your question, COMMON MODE NOISE... Consider the following image.. Without twisted pair the line closest to the noise source gets more noise than the other line. So the noise is no longer common mode. By twisting the wires you negate, or significantly reduce this effect. Telephone systems are, or were, all transformer based, which is ...

7

In the US (and pretty much everywhere else, though I won't claim to know how things are done in very rural or poor countries), the telephone cable plant (the run from your home to the central office) is twisted pair, not "single stranded". It's just not as tightly controlled in spec as Cat 5. You need to connect the two wires of the incoming pair to the two ...

6

Unshielded Twisted Pair has existed for as long as phone lines have existed, but it was originally designed to reject noise at audio frequencies. It was not designed with the correct number of twists to reject noise at the high speed digital frequencies of Ethernet. Coaxial cable, however, had long been in use for various RF applications, and its ...

6

I'm not entirely certain of this, but given who advanced this 1000BASE-TX standard, namely TIA (aka the cable people, the standard being TIA-854) and not IEEE, I have the strong impression that it was largely a promotional exercise for Cat 6... a standard which is also defined by TIA. This impression was reinforced by reading how this standard was described ...

6

A shield usually makes a pretty good protector against electric field disturbances (half the story) but, unfortunately, makes a pretty poor protection against magnetically coupled noise (the other half of the story). Twisting the conductors in a pair mainly ensures that induced voltages (due to external magnetic disturbances) are equalized on both ...

5

A possible negative effect could be the resistance of the wire. That's not caused by the twisted pair, but rather the wire diameter. If they're really signal wires the diameter will be rather small, and have a non-negligible resistance. The resistance will cause a voltage drop, which may become noticeable at longer distances. If the wire is thick enough ...

5

First, the technocal answer: For one, USB3 and SATA both use thin stranded twisted pairs (USB3 spec states to mak the cable 'as thin as possible', with 26-34 AWG given as example). 10GbE uses four solid relatively thick twisted pairs (23 AWG minimum). The thicker and solid strands create a larger surface area which in turn means lower resistance to high ...

4

Well, I gotta rush but https://www.dataforth.com/catalog/pdf/an507.pdf answers your question qualitatively Cable shielding is used primarily to minimize or eliminate capacitively coupled interference from electric fields. When properly implemented, it can also be used to minimize inductive coupling from magnetic fields. Shielding is only effective ...

4

I suspect HDMI to Cat6 converters don't actually contain baluns, because as you point out HDMI TMDS signals are balanced signals just as UTP pairs are balanced. In the days before HDMI, video signals were generally carried on coaxial cables. To avoid using expensive coax, many manufacturers came up with a method to use cheaper Cat5 cable instead. Since ...

4

While the whole idea sounds dodgy, I don't see why you need discrete wires to make a twisted pair. Criss-crossing diagonal traces on two adjacent layers, connected at short intervals by plated-through holes will do the same thing. Think of it as a series of X's (when viewed from above), with each segment terminated by a via.

4

Essentially, I'm only using one conductor of each twisted pair. Actually, you're using 2 conductors. One conductor of the twisted pair, and another that you haven't specified, which returns the current, or is the reference voltage. It will be there, even if you don't know where it is at the moment. Is a ground conductor in the cable, or a ground loop from ...

4

In a moment of inspiration, I realised that the braided shield being made of copper can help with attaching the aluminium foil. Basically the braid shield is split into four bundles, then each bundle can be wrapped around each of the twisted pairs - around the outside of the foil. Once done, you basically end up with four individual S/FTP cables. I should ...

4

There are two key advantages to twisted pairs Reduced inductance $L = N^2 \cdot \frac{\mu \cdot Ae}{l}$ by twisting the wires together you are reducing $Ae$ the enclosed area and so the inductance. Twisting the wires together means they are close together and so any noise picked up in one conductor should also be picked up in the other. A ...

4

why do twisted pair of cables have less cross talk between them The dominant reason for twisting wires is to cancel out interfering magnetic field induction. If two wires are not twisted, the wire closest to the interfering source has induced into it a greater voltage than the wire further away. So, if the wires are repeatedly crossed, the net induction ...

3

I've had problems with a similar arrangement where the R.H. 3V3 regulator circuit needed better decoupling to prevent switch-mode currents taking a partial route through data screens that were grounded at both ends. I'm not saying don't ground at both ends, just be careful about the 3V3 regulator if it is a switcher. The problem manifested itself as ...

3

Even or odd is not significant for the cable lengths in question. What is more significant is the number of twists per unit of length (and this is also the reason why the specifications limit the amount you are allowed to un-twist when mounting). Instead, the number of twists are even so that no switch of signal polarity occurs along the cable. Make the ...

3

The most common installation of Cat-5 cabling for network communications is to 10Base-T standards. This means 2 pairs, typically blue and green, will be carrying data. Blue has 72 turns per meter, and green has 65 turns per meter. Over short distances, none of this matters. You could have ribbons wrapped around fluorescent lights connecting your network ...

3

I would say that it is a tradeoff between the price of interfaces and the price of using more expensive cables (and having to change the cables in buildings). 100BASE-TX needs Cat5 cable and 62.5MHz bandwidth. 1000BASE-T expects Cat5e cable and 125MHz bandwidth. 1000BASE-TX needs Cat6 cable and 250MHz bandwidth. Cat5e is certainly much cheaper than Cat6 ...

Only top voted, non community-wiki answers of a minimum length are eligible