Simple broadband noise source

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 4:1 transformer is 8 bifilar turns on a Siemens/EPCOS B64290P37X33 ferrite toroid. An FT37-43 could be used.


My prototype, using very ugly construction.


A PCB I've designed for it. It's single-sided, with hatched copper pour for the ground connections, intended for making at home. I put in the wire link to avoid running a track between the transistor pads.

PCB designed with Pulsonix.

73, Leon
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