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I collected spread spectrum signals at 400 MHz at low elevation angles using Software Defined Radio complex sampling over the seasons. I noticed that over watery, icy surfaces, the RF samples are conjugated compared with regular open space RF samples, resulting in failed de-spreading. De-spreading works if the signal samples are conjugated. I like to think that this phenomenon can be because the 180 deg. reversal of H vector of the wave front in reflection causing |E x H|atan(-H/E) resulting in a 90 deg. change of phase. This answer just doesn't appear to be convincing. Search the Net, could not find any related report on reflected RF signal has signal sample conjugated. Any suggestions?

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  • $\begingroup$ Interesting question. I assume you've ruled out any misconfiguration of your receiver (i.e. if it has configurable spectral inversion, for example). $\endgroup$ – Jason R Apr 16 '15 at 17:03
  • $\begingroup$ I used the same de-spreading routine and the same setup for all other samples successfully. When this RF sample de-spreading failed, that is when I worked out that the failed RF sample has conjugation. All is again well after conjugation of the sample...Yes. I agree that the only possible answer is spectral reversal but just not comfortable blaming this on water and ice... $\endgroup$ – user4789322 Apr 16 '15 at 19:04

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