ZachTek WSPR transmitter

These are handmade in Sweden, although there is a Chinese rip-off that is available for much less. I think if files are available on the internet there is always a danger of this happening. 

I am not sure what protection registering the design gives, but I guess it must offer some help.

As I understand things, the Chinese rip-off does NOT contain switchable low pass filters, so the harmonic output is unlikely to be very good.

See https://www.zachtek.com/product-page/wspr-desktop-transmitter