A global geographical survey of received signal strength in the VHF band

Sumbandila (SO-67) is an 81 kg LEO satellite launched on 17 September 2009. Its primary payload is a multi-spectral imager with a ground sampling distance of 6.25 m at an orbit altitude of 500 km. Its two command transceivers operate in the commercial and amateur radio VHF and UHF bands and one of them provides a VHF to UHF repeater service to radio amateurs. This paper presents initial results of a global three week monitoring period of two VHF frequency ranges. The data is obtained by executing on-board flight control procedures to select the frequencies to measure. The existing on-board telemetry gathering system is employed to record the data, most notably the received signal strength for the selected frequency. The data is downloaded using an adaptation of the imagery data download path. We determine regions of high signal levels by distributing individual measurements over cells in the satellite footprint before averaging over the cells. The data is then plotted on a geographical signal strength heatmap. We compare our results with that of a similar study of the late 1990s and point out changes since then. The data provides useful information for selecting future ground station locations for minimum interference. It further gives an indication of frequencies to use for command and telemetry communication at existing ground stations. We propose that including a receiver capable of measuring frequency interference across a desired frequency range is very useful to future missions for selecting communication frequencies from this range for ground station locations.