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Author Topic: Building an RF Noise Generator For Testing Filters  (Read 2058 times)

Offline ChrisSmolinski

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Building an RF Noise Generator For Testing Filters
« on: August 30, 2016, 2154 UTC »
Itís often handy to have an RF noise generator when testing various circuits, especially filters. I was working on a low pass filter for long wave, and wanted a way to measure the performance of the filter.

This is the noise generator I came up with. Itís a fairly simple circuit: http://www.radiohobbyist.org/blog/?p=1884
Chris Smolinski
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Offline Zazzle

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Re: Building an RF Noise Generator For Testing Filters
« Reply #1 on: September 08, 2016, 1533 UTC »
Hey Chris,

Oh, I didn't knew that Z-Diodes produce that much noise as well.

I've build such, too but used a BC547. Basically with C left open, B connected to the Amp stage and E being fed with a tiny current. Actually, it's the voltage level that get's the thing going. The key is to bias the Diode section (whether it may be an actual diode or transistor) in reverse direction until it hits the breakdown limit. What produces the noise is actually thd "current jumping over the barrier". Since this happens not on a constant level but in small peaks it'll produce that broadband white noise.

Funny fact: couple the outputs of two noise generators and hook them up to your home PA. The signal you'll get sounds like you're at the beach of the sea, with waves rushing in again and again. :)

Kind gereetings,
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