I want to test filters and once again Santa stiffed me on all the fancy test gear I wanted.  It could be my fault as my chimney leads to the boiler.  Anyway, I have an rtl-sdr and an upconverter so all I needed was some clean noise.  Searching lead me to N5ESE's description of using a zener diode.  He references an earlier design by N0SS.  N0SS is now SK and his website is no longer but thanks to archive.org I found this https://web.archive.org/web/20050331110118/http://www.n0ss.net:80/noise_source.pdf
I breadboarded N0SS's circuit


and lo and behold it works great.  Below shows without and with the noise circuit.  The upconverter adds an offset of +125MHZ


if you are a Spielberg fan and live on a Native American burial ground you should probably skip this.

Doug
AC9RZ