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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
microvolts, is V
, then the signal-to-noise ratio, S/N, in decibels is given by the
n
formula
If V
= V
, then S/N = 0. In this situation, the signal borders on unreadable, because
s
n
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
s
10.0 microvolts and V
This results in the signal being clearly readable. If the signal is much weaker but still
above the noise -- say 1.30 microvolts -- then
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
s
n
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.
S/N = 20 log
, so S/N is positive. As an example, suppose that V
n
= 1.00 microvolt. Then
n
S/N = 20 log
(10.0) = 20.0 dB
10
S/N = 20 log
(1.30) = 2.28 dB
10
48
, and the noise level, also in
s
(V
/V
)
10
s
n
=
s
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