Abstract: A beacon transmission signal comprises at least one carrier (C+SB) including sidebands (SB) and one sideband only signal (SBO), said carrier and said signal being in any mutual phase relationship. The method of the invention includes the steps of demodulating the sum of the carrier (C+SB) and of the signal (SBO), on one hand by multiplying it by a frequency (F), and on the other hand by multiplying it by the same frequency in phase quadrature, extracting from the products continuous components representative of the carrier portion (C) of said carrier (C+SB) and the low frequency components of the beacon transmission signal representative of the sideband portions (SB) of the carrier (C+SB) and of the signal (SBO), calculating the module and phase of portion (C) of the carrier (C+SB) and deriving from the low frequency components the amplitudes of the sidebands (SB) and the amplitude and phase of the signal (SBO).