The idea of the VNARefit project comes from the https://www.electrolab.fr/ stock :) There are available old VNA test set everywhere in various shape and state. The common point to all these setup is to be bulky and noisy, plus they often cost a lot when you have to repair them. But in fact only 1 or 2 part of the setup are interesting !
Usual old VNA Stackup
On this picture you can see one classic configuration of the HP8510C VNA. The bottom rack is a YIG based generator controlled by the VNA to generate the test signal. This part is still usable today and those are often pretty good in term of phase noise (thanks to the YIG), be careful some of them are not synthetized so they have a non negligible long term drift. All in all those are good generator and should be saved !
The two rack on top are the main problem. They are basically a display and memory (computer) for the upper part, and an analog/digital signal processor just below. Those part are basically exchangeable with a computer… The goal of this project is to replace these part (and to replace the diode mixer often found behind the old testset).
The last part is the most interesting in our project, it's the coupler, in fact inside the box there are often 2 (or more) coupler or VSWR Bridge and some RF relays.