A broadband noise source is useful for testing purposes. This circuit gave a reasonably flat output up to 30 MHz when checked with a general coverage receiver. The output impedance is about 50 ohms. It's basically a zener diode used as a noise source with a broadband RF amplifier. I think the higher power zeners give more noise, which is why I used a 1W device. The zener voltage isn't critical, of course; use whatever you have around 6V. The 4:l transformer is 8 bifilar turns on a SiemensEPCOS B64290P37X33 ferrite toroid. An FT37-43 could be used.