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How to add noise to a sine wave to test filter
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Dmeads:
Hi all trying to test some filters and I am wondering if there is a way to add a little noise to a sine wave? I have basic lab equipment but maybe I can just use a really long wire from function generator to filter? I heard long jumper wires can add some noise.
moffy:
Use a summing inverting opamp with two resistors as inputs, one for your sine wave and one for the noise. For the noise source you could use a zener with lots of AC amplification, or a digital pseudo random generator with a filter to limit the bandwidth of the noise.
OM222O:
if you're not drawing significant current and just want to test a filter circuit, use a signal generator with 2 channels: 1 to produce the sine wave, 1 to produce the noise, then connect them in series. if you only have access to a single channel signal generator, try some of the noise generator circuits which use the 74 series logic to make white / red etc. noise, the reduce the amplitude (maybe with a potential divider followed by a buffer amp) and again, connect the outputs in series.
NiHaoMike:
If you're working within the audio range, use an app like Audacity to make a noisy sine wave.
Seekonk:
I picked up a couple pink noise generators used to make masking noise in office PA systems.  It only used two common CMOS chips to do it.  We had a noise injector made from two big big motor contactors in a relay race boxed in a giant piece of foam. Great test for line noise.
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