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The performance of a handheld Vector Network Analyzer (VNA), the nanoVNA, a low-cost, open-source instrument, was evaluated. The instrument measures the complex permittivity of dielectric media from 1-port reflection parameters in the 1 – 900 MHz bandwidth. We manufactured an open-ended coaxial probe using a SMA-N coaxial adapter to perform dielectric measurements. The accuracy of the nanoVNA was comparable to that of a commercial VNA between 1 and 500 MHz according to tests in reference organic liquids, while a lack of stability was found beyond 700 MHz. The self-manufactured open-ended coaxial probe was subjected to a Finite Element Method (FEM) analysis and its electromagnetic (EM) field penetration depth was determined to be 1.5 mm at 100 MHz, being reduced to 1.3 at 900 MHz and thus demonstrating a frequency-dependent support volume. The broadband complex permittivity of three mineral soils of varied textures was obtained for a range of bulk densities and water contents from dry to water-saturated conditions. The dielectric response of the soils approximated the well-known Topp et al. (1980) equation at high frequencies. At lower frequency however, higher permittivities were exhibited due to dielectric dispersion, which emphasizes the importance of EM-based soil moisture sensor operating frequency when considering sensor calibration or comparing the response of different sensors. This research was funded by Agencia Estatal de Investigación (AEI), project numbers: AGL2016-77282-C3-3-R and PID2019-106226-C22 AEI/https:///https://doi.org/10.13039/501100011033 | Ministerio de Educación y Formación Profesional, grant numbers: FPU17/05155 and FPU19/00020. Funding for David A. Robinson was provided by a Natural Environment Research Council (NERC) award number NE/R016429/1 as part of the UK–ScaPE Programme Delivering National Capability. We also acknowledge funding from the Polish National Agency for Academic Exchange, grant number: PPI/APM/2018/1/00048/U/001. The authors wish to thank Agencia Estatal de Investigación (AEI), Ministerio de Educación y Formación Profesional, Natural Environment Research Council (NERC) and Polish National Agency for Academic Exchange (NAWA) for the funding provided. The authors also wish to thank Juan Antonio Albaladejo for his help in machining the experimental OE coaxial probe.