  In this paper we present the European Low Frequency Survey (ELFS), a project
that will enable foregrounds-free measurements of the primordial $B$-mode
polarization and a detection of the tensor-to-scalar ratio, $r$, to a level
$\sigma(r) = 0.001$ by measuring the Galactic and extra-galactic emissions in
the 5--120\,GHz frequency window. Indeed, the main difficulty in measuring the
B-mode polarization comes from the fact that many other processes in the
Universe also emit polarized microwaves, which obscure the faint Cosmic
Microwave Background (CMB) signal. The first stage of this project is being
carried out in synergy with the Simons Array (SA) collaboration, installing a
5.5--11\,GHz (X-band) coherent receiver at the focus of one of the three 3.5\,m
SA telescopes in Atacama, Chile, followed by the installation of the
QUIJOTE-MFI2 in the 10--20 GHz range. We designate this initial iteration of
the ELFS program as ELFS-SA. The receivers are equipped with a fully digital
back-end that will provide a frequency resolution of 1\,MHz across the band,
allowing us to clean the scientific signal from unwanted radio frequency
interference, particularly from low-Earth orbit satellite mega constellations.
This paper reviews the scientific motivation for ELFS and its instrumental
characteristics, and provides an update on the development of ELFS-SA.
