Sometimes it is necessary to produce a wide-band noise.
I use for it a noise generator , which was meant actually for an noise bridge.
The construction on a universal circuit board with stripy circuit paths facilitates the construction. The interruptions in the conductive strips I realized with a drill with 4 mm diameter. I turned these with the hand, until the conductive strips in the appropriate place was interrupted.
I replaced the original transistors by RF transistors from the junk box. A strong noise can be achieved by this small device over the whole short wave frequency-area.
 Alois Krischke, DJ0TR: Rothammels Antennenbuch. 13. Edition, Baunatal 2013, Ch. 188.8.131.52 Antennenrauschbrücke, p. 1031