Analog Signals and Noise

An analog telephone signal is similar to water moving through a pipe.  The further the water has to move, the less strength the signal.

Simarlarly, the signal being analog, weakens as it travels over great distances no matter the medium (copper, coax cable, air, etc.).  This causes the analog signal to fade or weaken.  In voice converstaion this is presented as the voice getting softer and less distinct.

In addition to becoming weaker, the signal picks up little bits of electrical interference or “noise”.  Power lines, lights and electrical equipments all inject noise into the signal in the form of electrical energy.

In analog signals this noise is heard as static.

To overcome resistance and boost the signal strength, an analog signal is periodically strengthened with a device called an amplifier.

Amplifying a weakened analog signal is not without problems.  In analog services, the amplifier that boosts the signal can not tell the difference between the signal and the noise.  So both end up getting amplified.

In a voice telephone call that is carried by analog signals people will hear static on the line whenever this happens – but they can still (hopefully) hear what is being said.

When noise on data transmissions is amplified however, the noise may cause errors in the transmission.