The Wideband Digital Low-Frequency Radio Receiver WDLFRR is mainly intended for scientific applications. The portable battery-powered instrument has the capability to record electric field strengths in the frequency range from ~4 Hz to ~400 kHz with a sampling frequency of 1 MHz, an amplitude resolution of ~35 µV and a timing accuracy of ~12 ns whilst performing continuous digital waveform recordings for several days. The instrument strictly follows a modular design such that it can be extended to higher frequencies and timing accuracy when the corresponding digital technology becomes available. The low-cost radio receiver can be developed into an interferometric network by synchronizing individual radio receivers to map the low-frequency radio sky. The first measurements of atmospheric electric fields are carried out at Exmoor National Park in Southwest England to illustrate the capabilities of the novel instrument.