Propagation comparisons at VHF and UHF frequencies

This paper presents and compares measured propagation data taken at four unlicensed-band frequencies including 151 MHz, 433 MHz, 902 MHz and 2400 MHz. A custom 10 mW signal source was used as the transmitter, and a spectrum analyzer as the receiver to provide accuracy to within 1 dB and sensitivity to better than -120 dBm. Both monopole and low-gain directional antennas were employed to represent expected use in an Energy Harvesting application. The measurement environment included both indoor and outdoor features. A range of up to 1.5 km at the lower frequencies was achieved. The path-loss exponent was found to be approximately three to five and relatively independent of the operating band. Results confirm that lower frequencies are preferred for low-power applications when omni-directional and low gain antennas are used.