Topband: Polarization on 160m

[Robert Parkes]

Polarization on 160m

Interesting discussion and one I suspect we wish could fully comprehend !

When the wave front meets the ionosphere and the wave splits the 
critical frequency is different for the two waves, commonly known as foc and fxc. 
This difference (from memory) is half the gyrofrequency and can often be seen on 
Ionosonde plots with two sets of reflections. The gyro frequency 
depends on the strength of the magnetic field at that point of the 
ionosphere so can vary from 700kHz to 1.4MHz where the radiated wave interacts with the Ionosphere Layer be it, E layer or F layer.

Being radio amateurs and pushing the envelope we are trying to make 
that illusive QSO so we need to excite a propagation path which is 
normally at the limit in order to chase the DX.
Assuming conditions are favourable, and if the angle of arrival and 
critical frequency is such that it favours both wave fronts then for a 
single and multi-hop transmission both the O-wave and the X-wave will 
be propagated.

The higher frequency of the two wave fronts, the X-wave may propagate 
which could result in a QSO whilst those around us may not have quite 
the same favourable conditions and only the O-wave is propagated  on a differeing path while the X-Wavecould fall by the wayside and not be propagated. 
One result of all this variability could result in what has been called spotlight or torchlight propagation.  I recall Eric K3NA giving a talk along these lines when referring to 3B7C 160m operations and how that spotlight moved across North America during the course of his opening to the US.
There is a possibility that Circular Polarisation would assist with both the O and X wave modes of propagation and it could be argued that a "compromise" Inv-L antenna provides this with its Vertical and Horizontal elements making up the antenna and resulting mixed polarisation.After all a number of amateurs have had good success with an Inv-L.  

73sBob ParkesG3REP(ex - S21YP, 4S7RPG, A45XF, VS5RP, P29PR)