Planet-technology VC-200S Manuel d'utilisateur télécharger pdf (Page 48)

4.1.2 Line Configuration

Signal-to-Noise Ratio, often written S/N or SNR, is a measure of signal strength

relative to background noise. The ratio is usually measured in decibels (dB).

If the incoming signal strength in microvolts is V

, and the noise level, also in

microvolts, is V

, then the signal-to-noise ratio, S/N, in decibels is given by the

formula

S/N = 20 log

)

If V

= V

, then S/N = 0. In this situation, the signal borders on unreadable, because

the noise level severely competes with it. In digital communications, this will

probably cause a reduction in data speed because of frequent errors that require the

source (transmitting) computer or terminal to resend some packets of data.

Ideally, V

is greater than V

, so S/N is positive. As an example, suppose that V

10.0 microvolts and V

= 1.00 microvolt. Then

S/N = 20 log

(10.0) = 20.0 dB

This results in the signal being clearly readable. If the signal is much weaker but still

above the noise -- say 1.30 microvolts -- then

S/N = 20 log

(1.30) = 2.28 dB

This is a marginal situation. There might be some reduction in data speed under these

conditions.

If V

is less than V

, then S/N is negative. In this type of situation, reliable

communication is generally not possible unless steps are taken to increase the signal

level and/or decrease the noise level at the destination (receiving) computer or

terminal.

To select the direction and target SNRM of line, click on the Line Confing link in the

left navigation bar, show as below.

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Planet-technology VC-200S Manuel d'utilisateur Page 48