  SPARC_LAB is a high-brightness electron photoinjector dedicated to FEL
radiation production and research on novel acceleration techniques. It has been
in operation at LNF since 2005. It is composed of a newly designed brazeless
1.6-cell S-band RF gun, two 3 meter long travelling wave S-band accelerating
structures, and a 1.4 meter C-band structure that acts as an energy booster.
Recently, a plasma interaction chamber was installed to study and optimize
beam-driven plasma acceleration schemes. During fall 2023, a major upgrade of
the entire low-level RF (LLRF) system will take place to consolidate and
improve performance in terms of amplitude, phase resolution, and stability. The
original analog S-band and the digital C-band LLRF systems will be replaced by
commercial, temperature-stabilized, FPGA-controlled digital LLRF systems
manufactured by Instrumentation Technologies. Additionally, the reference
generation and distribution will be updated. In parallel with this activity,
there is a growing interest in X-band LLRF at LNF due to the
EuPRAXIA@SPARC\_LAB project. This project aims to build an FEL user facility
driven by an X-band linac at LNF in the coming years. To test X-band RF
structures and waveguide components, a high-power X-band test stand named TEX
has been installed and recently commissioned. A detailed view of the TEX LLRF
system, based on a commercial S-band system with a dedicated up/down-converter
stage, will be discussed, along with the limitations of such an approach.
