Author Topic: How to add noise to a sine wave to test filter  (Read 1340 times)

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Offline DmeadsTopic starter

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How to add noise to a sine wave to test filter
« on: October 06, 2019, 01:36:25 am »
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.
 

Offline moffy

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Re: How to add noise to a sine wave to test filter
« Reply #1 on: October 06, 2019, 02:49:38 am »
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.
 

Offline OM222O

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Re: How to add noise to a sine wave to test filter
« Reply #2 on: October 06, 2019, 01:28:34 pm »
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.
 

Online NiHaoMike

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Re: How to add noise to a sine wave to test filter
« Reply #3 on: October 06, 2019, 01:52:08 pm »
If you're working within the audio range, use an app like Audacity to make a noisy sine wave.
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Offline Seekonk

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Re: How to add noise to a sine wave to test filter
« Reply #4 on: October 06, 2019, 02:22:04 pm »
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.
 

Offline moffy

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Re: How to add noise to a sine wave to test filter
« Reply #5 on: October 06, 2019, 11:55:51 pm »
You don't even need the opamp to add the noise, just two resistors joined together, one for the sine the other for the noise.
 


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