What is a channel?
The connections between a transmitter and receiver. Such as a combination of electrical cables, optical fibres, radio links and associated repeaters.
How is power transferred efficiently?
By maximising the power transferred to the load from the source.
When does maximum power transfer occur?
Maximum power transfer is therefore achieved when RSource = RLoad.
Noise Floor
Minimum usable signal determined by the noise characteristics of channel elements (amps, cables, antennas, filters, antennas …) and how well they are tolerated.
Maximum signal
- Upper limit on signal amplitude in channel.
- Exceedance results in clipping of waveforms as they approach the power rails.
- Limited by sparks formed when materials ionise or break down.
Dynamic range
Ratio of largest to smallest signal that the channel can support.
Dispersion
- Signal spreads out.
- Time spread cause by continuous process or caused by multiply delays signal echos.
- Causes pulse to spread out in time domain becoming less distinct, and USB arrives before USB in freq domain due to change in speed of frequency components.
The phase shift induced by the delay τ is:
φτ = − ωτ
Phase Delay:
τφ = − φ/ω
Group Delay:
τg = = − ∂φ/∂ω
Why is Group Delay important?
- information is delayed by group delay
- As a single tone has no information
If the phase and group delay are independent of freq:
- All of the components of a signal are delayed by the same time. The phase shift depends linearly on frequency: φ = −ωτ.
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If the phase and group delay are a function of frequency:
Components of a signal are delayed by different times and there is Delay Distortion.
Describe a Buttersworth filter
- Time delay variation is modest across the pass band.
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Describe a Chebyshev filter
- Near brick wall characteristics
- Definable ripple in the pass band
- Time delay dispersion can be very significant.
Describe Bessel Filter
- Near linear phase with frequency/ very little delay distortion
- Slow transition from pass band to stop band.
