Remote sensing of the primary component of cosmic 11-year and diurnal variations over a wide rigidity range is carried out by nonlinear inversion of the Fedholm integral equation relating secondary variations to the primary spectra. Data from three and four stations are simultaneously analyzed, using recently developed coupling functions based on Feynman scaling hypothesis. The range of rigidity over which the retrieval of the primary spectra is possible is investigated. Information content of measured intensities is studied by eigenanalysis of the covariance matrix of kernels of the integral equation. It is concluded that a redundancy of existing stations in the low range and a lack of stations in the high rigidity range already exist. Implications, suggestions, errors, and possible extensions are discussed.