Power: Given the remoteness of Diablotin’s nesting sites (30 miles from the coast, ~2,000m above sea level, in the Sierra de Bahoruco National Park, Dominican Republic), I needed to rely on gear that easily be transported and adapted in the field (with limited access to electricity), withstand fog, rain and humidity, was allowed on international flights (cheaper than shipping to the Dominican Republic), could and was as cheap as possible. To power the base-stations, I chose Li-ion powerbanks as they are allowed on regular flights and (unlike car batteries) are easy to transport and affordable. Most regular powerbanks, though, have a safety feature that stops sending power when the device they recharge does not draw enough current: this is to avoid over-charging a fully-charged device. Since the Mataki-CLASSIC base-station draws very little current, typical powerbanks stopped after a few minutes. For this reason, I used Voltaic Systems’ V44 battery packs as their “Always On” feature is designed for low-power IoT.
Circuit: Since the battery’s 12,000mAh weren’t sufficient to keep the base-station safely running for the tracking period I needed (~ 1 month, at 480mAh per day), I paired it with a 5.5W solar-panels. The circuit was minimal (attachment 1): the solar-panel recharged the V44 battery, which delivered 5V-2A in “Always-ON” mode. The 5V-3.7V step-down regulator connected the battery to the base-station, in parallel with the 1,000µF capacitor.
Antenna: Given the dispersion of the nests of tagged petrels, I chose an omnidirectional antenna. A directional, Yaggi-antenna could have been helpful for downloads from a distant vantage point, had the nests been clumped together. Each antenna had a maximum range of ~300m in open terrain but irregular relief and dense vegetation decreased that distance to ~100m. Note that in our region, the authorized UHF channel for private communications is 916mHz – this frequency might be different in other regions.
Enclosure: I enclosed the base-stations in a very simple version of this waterproof solar battery case, using a 1040 Pelican case: I trusted Pelican cases to have a good quality/price ratio. The battery barely fitted inside the case (I had to shorten the male 5.5x2.1mm input plug). While I still drilled a hole in the case, I didn’t use the M60 nut. Instead, I covered the hole and the cables (for the antenna and solar-panel) with Sugru and waterproofed them with 2-part epoxy: this allowed me to adapt the base-station more easily to the local conditions. For good measure, I also added a handful of desiccant packs into the case. Finally, I deployed the base-stations in open canopy, as close to the nests of the Black-capped petrels we tagged as possible. I tried to position the solar-panel to face the midday sun, a time when the morning fog had already burnt off but the afternoon clouds not yet rolled in (attachment 2: Deployed base-stations).