[HCDX] Re: Groundwave propagation on SW

["Julian Hardstone" <j.omega@xxxxxxxxxxxxxxxxx>]

Bogdan wrote:
>
> I have a question for those of you specialists on the propagation of radio
waves. How far from the tx-site, a SW signal can reach without being
reflected by the ionosphere thousands of kilometers away or so ? <<

I don't know the precise answers to this, which will, in any case, depend on
Tx power and frequency. But in thinking about this, it's worth making the
distinction between groundwave and skywave. SW broadcast transmissions
intended for ionospheric propagation are almost always horizontally
polarised, and are transmitted, from horizontal dipole arrays, without
launching any vertically polarised *groundwaves* along the fuzzy boundary
between ground and air.

The HP wave will become tilted when it hits the ground, giving a localised
VP wave, which can then be received on a vertical antenna. But the major
propagation mode for HF signals which are not received via the ionosphere,
is space-wave, same as at VHF and above, where the main loss of signal is
due to cancellation between the direct signal and the reflections from the
ground.

True ground wave propagation is what occurs at MF and below, where
vertically polarised signals are launched along the ground surface, and the
propagation losses can be accurately predicted, knowing the frequency and
the ground resisitivity.

Just something to think about.  8)


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