Highly Portable, Low-Cost SDR Instrument for RF Propagation Studies

Software-defined radio (SDR) instruments can be used to replace bulky and expensive spectrum analyzers for RF field measurements. Using the commercial off-the-shelf (COTS) equipment, a low-cost, portable SDR instrument for measuring RF propagation has been created and tested. In the U.K., parts of the very high-frequency (VHF) spectrum have been repurposed for the use of Internet-of-Things devices; the instrument developed here is designed to meet the use case of performing an urban propagation study in VHF and UHF short range devices bands in a fast and low-cost manner. Design of the hardware and software is discussed, as well as the calibration of the instrument. The results of a test propagation study are given for the completed instrument. It is shown that the SDR instrument is capable of performing the study to a high degree of agreement with a commercial spectrum analyzer, thus validating the approach. The readings of the received power taken by the instrument are shown to agree with the readings taken at the same locations with a commercial spectrum analyzer to within an average of 1.4 dB at 71 MHz and 1.1 dB at 869.525 MHz. From the measurements taken, log-distance models were able to be produced with a path-loss exponent of 2.44 and a log-normal shadowing standard deviation of 8.5 dB at 71 MHz, and a path-loss exponent of 4.06 and a log-normal shadowing standard deviation of 8.8 dB at 869.525 MHz.