Beware: HF content !
In addition to the obvious time and frequency applications there is also a plethora of propagation science that can easily be accomplished by even us mere amateurs.
To demonstrate x and o mode propagation, I have often used a setup where I GNSS PPS trigger a regular analogue or digital oscilloscope measuring the audio beat of the received timing pulses. In this manner,the o/x mode superimposed, time delayed aggregate pulse can be observed and the individual time variant (multipath) fading of the LHCP and RHCP combination can be very easily observed and visually separated on the scope screen with a regular HF receiver and e.g. simple (linearly polarised) dipole.
Obviously both propagation paths can be observed separated in a similar manner using a dual channel oscilloscope and a circularly dual polarised HF antenna. Extremely interesting to study as the x and o mode MUF's creep past the frequency of observation as a function of E and F layer ionisation:
http://www.kolumbus.fi/michael.fletcher/HF_layer1_oblique_nvis_propagation_a...
http://www.kolumbus.fi/michael.fletcher/60m_band_1000km_oblique_o_mode_x_mod...
Michael OH2AUE