A wireline logging system for measuring formation resistivity includes a longitudinal housing having three transmitters and three receivers arranged at measured distances on the housing, with about four feet between the outermost ends of the array. The transmitters are operated at three different frequencies, with each receiver receiving all three frequencies. The output of each receiver is the three received frequencies, which is amplified and fed to a mixer. A local oscillator frequency is also fed to each mixer. The output from each mixer of the three received frequencies mixed with a local frequency is passed through a filter to output one of the three received signals at a lower frequency. The frequency mix is arranged so that the output of each of the filters is at a common frequency. The filtered outputs from pairs of the filters are then passed to phase comparators and/or amplitude ratio determining devices to provide signals indicative of formation resistivity which are then passed to the surface on the wireline.