System Design and Implementation of a Large-Scale Tracking System Based on VHF
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In this thesis a tracking system aimed at tracking sheep on free range pastures is designed. The system is based on the license-free 169.4000 - 169.4750 MHz frequency band. It tries to overcome problems related to existing commercial systems with regards to cost, battery lifetime and coverage. The system utilizes dedicated base stations which ensures satisfactory coverage anywhere required, in addition to a main station which includes a NarrowBand (NB) Internet of Things (IoT) module that communicates with an online database. The NB IoT module requires a subscription from a telecommunications company, but the system does not otherwise require any subscriptions. Cost comparisons showed that the presented solution is cheaper than all of the other commercial systems, especially in the long term. System architecture design is performed with corresponding link and energy budget analysis. Two revisions of printed circuit boards (PCBs) for the tracker module are designed, produced and tested. The first revision utilizes a helical antenna sealed in rubber, while a custom dipole antenna intended to be integrated as a part of the sheep collar is designed and implemented for the second revision. They are evaluated in terms of performance and compliance with regards to applicable regulations. The helical antenna yielded far better performance than the dipole antenna. The longest distance measured is 7.46 km, with line-of-sight propagation, with a link margin of 35.8 dB for the first revision and 19.8 dB for the second revision. Field experiments indicates an achievable distance of more than 10 km for the first revision in varied terrain and with non-line-of-sight propagation, but only 7.1 km for the second revision. Software is developed for the tracker module and the base station with an immense focus on high energy efficiency. Energy measurements revealed that the tracking device is far more energy efficient than existing commercial systems. A single AA battery yields an estimated lifetime of more than 36 years.