Sometimes I get asked about the origins of the SMA Simple Spectrum Analyser, the NWT-4000, etc.
This is what I found out so far:
The NWT devices where originally developed in Germany by amateur radio addicts. At one point this was featured in the magazine http://www.funkamateur.de.
The software (WinNWT and LinNWT) was written DL4JAL for this magazine and is documented on his web-seite: http://www.dl4jal.eu.
The initial devices were the FA-NWT, up to the NWT500, NWT7 and HFM9. They can offer a lot of extra functionality, like software controlled attenuator, etc.
The Chinese radio amateur BG7TBL cloned the design and used the ADF4350 chip for an increased frequency range. Other models followed up. They are all compatible with the original design, because they rely on the WinNWT/LinNWT software. Sadly, the Chinese selling the cloned hardware include the WinNWT/LinNWT without any authorisation, causing the author DL4JAL a lot of problems with people asking for help.
He does not reply, because a) he has nothing to do with these cloned devices and b) most support questions come from the cheaper models featuring only one ADF4350/ADF4351: they cannot be used for SWR measurements and hence the WinNWT/LinNWT software is not of great use.
It is to be expected that more and more models will follow up, as new synthesizer chips become available, which offer such increased frequency ranges.