If H and V are horizontal and vertical yagis, linearly polarised, and the signal is from VE3ONT, circularly polarised, The two tracks on the oscilloscope as described above, will be sine waves, of equal amplitudes, phase shifted by 90 degrees. There is something funny with black body radiation. The electromagnetic wave coming from outer space does not have any polarisation. The polarisation is created by the antenna, when the field is converted to a voltage across a gap in a conductor. An electromagnetic wave travels with the speed of light.
Travels means direction of movement.
Let us call the direction along which the wave travels the Z direction. Space has 3 dimensions, so there are two orthogonal dimensions X and Y left for the electric field that constitutes the wave to oscillate in. To describe the wave you need two independent variables in order to describe the random oscillation of the electric field vector in the XY plane. The voltage across a single feed point, being just a single variable, can therefore only describe certain aspects of the wave. To fully describe the wave, you need two simultaneous voltages, one for each dimension.