answersLogoWhite

0


Best Answer

The most common cause is improper wire usage such as using non-twisted pair within the home (doorbell wire or alarm wire instead of telephone wire). Another common issue is the cable in the outside plant becoming ungrounded or interference from the electric company wires. Below is a great description from Wikipedia.

Twisted pair cabling is a type of wiring in which two conductors (the forward and return conductors of a single circuit) are twisted together for the purposes of canceling out electromagnetic interference (EMI) from external sources; for instance, electromagnetic radiation from unshielded twisted pair (UTP) cables, and crosstalk between neighboring pairs. It was invented by Alexander Graham Bell.

In balanced pair operation, the two wires carry equal and opposite signals and the destination detects the difference between the two. This is known as differential mode transmission. Noise sources introduce signals into the wires by coupling of electric or magnetic fields and tend to couple to both wires equally. The noise thus produces a common-mode signal which is cancelled at the receiver when the difference signal is taken. This method starts to fail when the noise source is close to the signal wires; the closer wire will couple with the noise more strongly and the common-mode rejection of the receiver will fail to eliminate it. This problem is especially apparent in telecommunication cables where pairs in the same cable lie next to each other for many miles. One pair can induce crosstalk in another and it is additive along the length of the cable. Twisting the pairs counters this effect as on each half twist the wire nearest to the noise-source is exchanged. Providing the interfering source remains uniform, or nearly so, over the distance of a single twist, the induced noise will remain common-mode. Differential signaling also reduces electromagnetic radiation from the cable, along with the associated attenuation allowing for greater distance between exchanges.

The twist rate (also called pitch of the twist, usually defined in twists per meter) makes up part of the specification for a given type of cable. Where nearby pairs have equal twist rates, the same conductors of the different pairs may repeatedly lie next to each other, partially undoing the benefits of differential mode. For this reason it is commonly specified that, at least for cables containing small numbers of pairs, the twist rates must differ.

The earliest telephones used telegraph lines, or open-wire single-wire earth return circuits. In the 1880s electric trams were installed in many cities, which induced noise into these circuits. Lawsuits being unavailing, the telephone companies converted to balanced circuits, which had the incidental benefit of reducing attenuation, hence increasing range.

As electrical power distribution became more commonplace, this measure proved inadequate. Two wires, strung on either side of cross bars on utility poles, shared the route with electrical power lines. Within a few years the growing use of electricity again brought an increase of interference, so engineers devised a method called wire transposition, to cancel out the interference. In wire transposition, the wires exchange position once every several poles. In this way, the two wires would receive similar EMI from power lines. This represented an early implementation of twisting, with a twist rate of about four twists per kilometre, or six per mile. Such open-wire balanced lines with periodic transpositions still survives today in some rural areas.

Twisted pair cables were invented by Alexander Graham Bell in 1881.[1] By 1900, the entire American telephone line network was either twisted pair or open wire with transposition to guard against interference. Today, most of the millions of kilometres of twisted pairs in the world are outdoor landlines, owned by telephone companies, used for voice service, and only handled or even seen by telephone workers.

User Avatar

Wiki User

โˆ™ 2010-09-17 20:46:37
This answer is:
๐Ÿ™
0
๐Ÿคจ
0
๐Ÿ˜ฎ
0
User Avatar

Add your answer:

Earn +20 pts
Q: What causes noise or static on a telephone?
Write your answer...
Submit
Related questions

What force causes static charge?

Friction is the force that causes static charge


What is noise in image processing?

Noise is static, kinda like when your tv screwes up


The force of what causes static cling in a dryer?

Electricity is the force of what causes static cling in a dryer.


What causes static on 2001 Ford Ranger radio. Static increases as engine rpms increase.?

It's picking up the alternator as it spins. In some cases the radio or antenna may not be shielded anymore or if so equipped the noise suppressor has failed. You might be able to get a noise suppressor from a stereo shop.


What causes noise on TV when it goes to static?

What causes the noise on a television when it goes to static is background cosmic radiation left over from the Big Bang. The rays remaining in space interrupt the signals being sent to your television, causing the "static snow". If you have any other questions please feel free to e-mail me at: acgsports@sbcglobal.net Only about 1% of the static in the television is a result of the radiation coming from the cosmos. The rest is from a mix of the channel attempting to pick up a signal on the frequency it's on, other waves traveling through the television, and blank signal.


Sentences using the word static?

Static currents are very exciting. static water has energy.


What causes static?

friction


What should i do when the telephone rings and there is no one there only static?

It means you need to buy a new telephone service


What is static cling?

static cling is like when you pull a shirt out of the dryer and something is sticking to it and when you pull it apart it makes a spark noise that is static cling


Calculate the capacity of a telephone channel of 3000hz and signal to noise ratio of 3162?

Calculate the capacity of a telephone channel of 3000hz and signal to noise ratio of 3162?


What causes static electricity on an object?

it causes by negative ( - ) And posative ( + ) .


What is the difference between musical sound and noise?

We all like musical sounds and we hate static annoying noise.


Can noise be music?

No, music has to have a steady beat and a rhythmic pattern while noise can be anything from radio static to talking.


How does pink noise sound?

Both pink and white noise sound like static; pink noise sounds like white noise with the bass turned up a bit.


What causes static to increase and decrease?

no


Causes of noise?

it depends


Static noise on surround sounds sub woofer?

Static noise on speakers usually means the speaker wire is not shielded properly. Replacing the wire with high quality speaker wire will likely solve the issue.


What causes static elec in your hair?

friction.


What do the electrons do that causes static shock?

Jump.


What is the Name for noise which interferes with reception of a radio channel?

Static is the noise Occurs mainly on short, long and medium wave reception


What causes static electrcity?

static electricity is a stationary electric charge that is built up on a material


Does static friction or rolling friction causes a car tire to turn on the road?

static friction


What causes static sound on a TV?

Because sometimes the universe is shaking, and that is what causes it.


How does eliminating static electricity help or hinder the performance of a device?

Eliminating static electricity helps the performance of the device because it prevents the device from cutting out as much and picking up on static noise.


What causes tire noise?

tires