This paper describes the setup of a sampling-based ratio bridge for calibrating voltage transformers. The advantage of this ratio method is that voltage transformers with different transformer ratios can be easily compared. Initial measurements of the components of the bridge indicate low systematic errors, negligible voltage dependency and low phase errors around 50 / 60 Hz. This indicates an attainable uncertainty of below 2 ppm for the ratio error and \pmb0.5 μ rad for the...