SNR - Signal to Noise Ratio

SNR Nedir
Açıklaması şöyle.

Signal to Noise Ratio is the relation between the data signal level and the noise level. Even the most perfect cable absorbs some noise. This "noise" is electromagnetic interference produced by:
- Other cables running near the cable.
- Faulty connectors.
- Motors or transformers near the cable.
- Radio systems.

Wikipedia açıklaması şöyle.

Signal-to-noise ratio (abbreviated SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. SNR is defined as the ratio of signal power to the noise power, often expressed in decibels. A ratio higher than 1:1 (greater than 0 dB) indicates more signal than noise.

Interference (Girişim) Nedir
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When waves add in a superposition it is called interference. Two waves heading towards each other with have interference.

SNR Oranı Neden Önemli
Açıklaması şöyle.

If the noise is strong then the signal cannot be recognized.

Higher ratios means better cables. Below 10dB is very bad and more than 20dB is good.

At higher ratios, more speed can be achieved and lower ratios mean error-prone cable and lower speeds.

SNR Birimi Nedir
dB cinsindendir. Açıklaması şöyle.

It's a value measured in dB and it describes the relation between the signal strength to your house versus the noise, which affects your copper line. The noise is normally magnetic disturbance from high voltage cables etc. The higher the dB value is, the better your line will be, as the signal strength outperforms the noise.

Typical values are:

- 10dB and lower is bad
- 11db – 20dB is OK
- 20dB – 28dB is excellent
- 29dB and above is outstanding

SNR Margin Nedir
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The SNR margin is the difference between the SNR of the cable and the SNR needed to get an specific speed.

Suppose that the SNR of the cable is 34dB and the SNR to sync at 6Mb is 30dB, then the SNR margin is 34-30 = 4dB

SNR ve Mesafe
SNR mesafe arttıkça düşer. Açıklaması şöyle.

At long distances, your transmit signal loses a lot of power. As a result of that, the SNR at the receiver is possibly relatively low.

A low SNR means that you cannot transport many bits per second over that channel (Shannon limit).

Not having many bit/s means you can't push much data across, which means you must reduce the account of data in the digitized speech.

Bir başka açıklama şöyle

Usually, a transmitter has a fixed amount of available power. You either have a regulatory or economic constraint, or your RF front-end has a power amp of a certain wattage and that's what you're stuck with.

The transmitted power is attenuated over the distance between transmitter and receiver. The actual attenuation depends on the propagation environment, but in general the power decreases exponentially with the distance.

SNR Düşük İse
Sinyali daha uzun süre göndermek gerekir. Açıklaması şöyle.

The poorer the SNR, the longer you need to transmit to make it clear. Another way to say it is that when you have a noisy background, and you turn on the transmitter, it creates a statistical bias in the noise fluctuations as its transmissions become superimposed upon them, e.g. putting a sinusoidal variation on top.

At very low levels, this statistical bias is very small and thus requires a long sampling time to collect enough data to tease it out with high probability and since you don't know what data is coming at you by definition, you want the thing you're trying to tease to be as predictable as possible over the teasing time, and thus you must be sending only a single specific type of signal over that time and not switching between bits, limiting the bit rate to exactly that time.

A mathematical theorem called the Shannon-Hartley Theorem analyses this precisely and gives the exact bounds on just how fast you can transmit data and still have it reliably heard over a given level of noise relative to the strength of the transmitting signal.

Attenuation Nedir - Zayıflama
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Every cable on earth suffers of attenuation. It is a measure of how the signal loses strength when running through the cable.
Suppose you put 5 volts in the end of a 1 Kilometer cable. If you measure the voltage in the other end you get, for example 4.5 volts. There was an attenuation of the original voltage. If the cable was longer, for example, 5 kilometers then the voltage on the far side could be very low.

For data signal this is key because if the original signal is strongly atternuated it could be gibberish for the equipment.

Attenuation Birimi Nedir
dB cinsindendir. Açıklaması şöyle.

It's also measured in dBs and you can check the number on your ADSL statistics page. The closer you are to the ISP, typically the better speeds you can get. It also depends on the amount of users, who connect through the same copper. In short, the lower this number is, the better:

20dB and below is outstanding
20dB – 30dB is excellent
30dB – 40dB is very good
40dB – 50db is OK
50dB and above is bad