Hi,
1) You can PM me in your native German language, if you want - I am a native German speaker, too.
2) The (unofficial) forum, where my software is discussed almost on a daily basis is here:
https://www.satellites.co.uk/forums/threads/using-the-138mhz-4-4ghz-usb-sma-source-signal-generator-simple-spectrum-analyzer-for-tv-catv-sat.169694/3) My roots come from TV/CATV/SAT applications, which is why my software has some peculiar functions that appeal to i.e. SAT DXers.
4) The difference between the SMA Low cost model and the NWT400 model is that the first one has just one ADF4350/ADF4351 (138MHz-4.4GHz/35MHz-4.4GHz), while the NWT4000 has two such IC's. This effectively allows the NWT4000 device to SIMULTANEOUSLY emit and receive a signal, which is what you want for SWR measurements - it's basically a tracking generator, where both IC's are sync'ed so that one emits at a given frequency at the output port, while the other reads the power of said frequency in the input port. The device then sweeps this across the selected frequency range. Other than that, expect exactly the same curves on both devices, as they use the same synthesizer for frequency conversion, the same logarithmic converter and the same microcontroller.
5) I do not own a NWT4000 and hence I did not implement any special functionality in my software to benefit from having two ADF4350/ADF4351. I will NOT implement such a tracking generator, as doing so requires me to have a NWT4000, to figure out how the commands work. I *may* implement this functionality if/when donations reach a value that allows me to purchase such device.
6) You can use two SMA devices running my software in two separate sessions. This will still not allow use as a tracking generator, because there is no sync between both devices. I made tests, even with relatively long pauses in the sweep, but results are unusable.
7) You can do filter measurements using a noise source. This has been discussed before and I have written about this in my blog. You can buy relatively cheap noise sources designed by the same guy that designed the SMA/NWT clones: BG7TBL. They cost around 20 Euro and are low quality if compared with a "real" noise source, but excellent for the price they cost. I mention them in my manual, too.
Regards,
Vitor