Chapter
5:
Communications Link
Here is the
work-script for chapter 5 (slides)
5 November 2021
We learned about all the parameters that we need to develop
the link equation. We derived the equation for the
received power and explained the meaning of free space loss.
8 November 2021
We derived the link equation.
We talked
about system noise, introduced C/N, derived the simple
equation for the noise power
spectral density in the limit for radio waves, listed types of
thermal noise and studied the curve for sky noise as a
function of radio frequency.
10 November 2021
We derived
the equation for the system temperature. We talked about
the 3K
cosmic background radiation and Penzias
and Wilson who discovered it. Click
here for
the latest results from the Planck mission.
12 November 2021
We
introduced the noise factor and looked at absorptive network
noise.
We learned how
the equivalent noise temperature of a device can be
referred to the input and then also to the output of the
device. We looked at the differences between amplifiers
and passive attenuators. We looked at a block diagram of a receiver and
the equivalent input temperatures at different sections
of the receiver.
15 November 2021
We used an example and went through the
computation of the system temperature of the antenna and
the receiver. We also found and expression for the noise
power spectral density at the receiver output.
We realized
what Penzias and Wilson needed to consider to
conclude that there is a 3K cosmic microwave
background (CMB)
radiation in the universe. We talked
about LNA's. And then we turned to
the C/N ratio and introduced
the saturation flux density, the effective aperture of an
isotropic antenna and the back-off from the saturation point
of a transponder amplifier which is related to the
non-linearity of the amplification curve.
17 November 2021
We looked at
the combined uplink and downlink C/N. Then we distinguished
between
different kinds of noise, thermal noise, intermodulation noise
and intrasystem interference noise and learned that the
overall C/N is computed by adding the N/C's for the different
kinds of noise. Then we looked at an
example of a multicarrier satellite circuit at C-band and
computed the overall C/N ratio.
19 November 2021
We looked at how intermodulation noise is
determined experimentally.
22 November 2021
We
focused on computation examples and about what is needed
to communicate with hypothetical aliens in our
Galaxy. Click here
to check your calculations. Click
here for the 1974 broadcast with Arecibo into
space.
24
November 2021
We started on Chapter 6. We introduced different
kinds of analogue and digital modulation and then
focussed on analogue modulation. First we learned about
amplitude modulation, how to describe it mathematically
and how the spectrum looks. Then we turned to frequency
modulation.
26
November 2021
We continued studying FM and learned about
Bessel and the Bessel functions that are used to
describe the spectrum of FM.