## Elements of a Communications Link

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### Transmitter

#### The transmitter (TX) element processes message signal in order to produce a signal most likely to pass reliably and efficiently through the channel. This usually involves modulation of a carrier signal by the message signal, coding of the signal to help correct for tranmission errors, filtering of the message or modulated signal to constrain the occupied bandwidth, and power amplification to overcome channel losses.

### Transmission Channel

#### Loosley defined as the electrical medium between source and destination, e.g. cable, optical fibre, free space, the channel is characterised by its Loss/Attenuation, Bandwidth, Noise/Interference and Distortion.

### Receiver

#### The receiver (RX) function is principally to reverse the modulation processing of the transmitter in order to recover the message signal, attempting to compensate for any signal degradation introduced by the channel. This will normally involve amplification, filtering, demodulation and decoding and in general is a more complex task than the transmit processing.