  In this paper we present the European Low Frequency Survey (ELFS), a project
that will enable foregrounds-free measurements of primordial $B$-mode
polarization to a level 10$^{-3}$ 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 not just from its sheer faintness, but
from the fact that many other objects in the Universe also emit polarized
microwaves, which mask the faint CMB signal. The first stage of this project
will be carried out in synergy with the Simons Array (SA) collaboration,
installing a 5.5--11 GHz coherent receiver at the focus of one of the three
3.5\,m SA telescopes in Atacama, Chile ("ELFS on SA"). The receiver will be
equipped with a fully digital back-end based on the latest Xilinx RF
System-on-Chip devices that will provide frequency resolution of 1\,MHz across
the whole observing 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 on SA.
