I recently purchased an SV4401A from Aliexpress for $299. As a lab instrument, it is very nice, a giant step up from the F-V2. With up to 1001 data points, the sweep resolution is great. The N connectors are nice too, though a cal set of N types would have topped it off. It has mass and is ruggedly built, inside and out. The batteries are replaceable without soldering.
My unit has two serious issues, which I am trying to work through with the tech guy at Sysjojnt, who also developed the V2. The software nanovna-saver is picky about which Win10 pcs it'll run on. I get a failed to execute script msg. Strangely it runs on my cheap tablet and a desktop at work. Three others will not work. I am not a pc or Windows expert. Maybe there is a setting that will let it run? The other issue I have is that, when left off for a while unplugged, it will not boot. Instead, it cycles through a power on sequence indefinitely. The batteries are fully charged. So to take it outside I must bring a 5VDC power source with type C USB connector. Whether these problems are design flaws or just with my unit remains to be seen.
