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 Audio signal/function generator, audio analyzer 
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Joined: Sun Aug 26, 2012 2:08 pm
Posts: 1048
Location: Lacey, WA USA
I'm looking at using an AD9833 DDS sine/square/triangle wave generator. At 25MHz clock, it goes up to 12.5MHz output, although the output likely isn't that great at 1/2 the clock. But that has only 0.1Hz frequency resolution, and the XO on the board isn't that great.

So I'm thinking of replacing it with a TCXP 1MHz 0.5ppm oscillator. That should still have clean sine waves at 200kHz and have a resolution of 0.004Hz.

The AD9833 has 28 bit resolution on frequency and a 10 bit DAC. It can be used as a sweep frequency generator. It has outputs for sine, triangle, and square wave. You can get it on a breakout board with SMA connector for $12 to $15 USD.

Page 12 of the datasheet shows an example of a 60kHz output with the first harmonic about 62dB down from the fundamental.
AD9833 Datasheet

App Note AN-1044 about making a sweep generator out of a similar Analog Devices DDS:
http://www.analog.com/media/en/technical-documentation/application-notes/AN-1044.pdf

AD9833 Waveform Generator

Conversation about AD9833 to a Nano Arduino on this forum

As per the conversation at the above link, you can decrease the clock crystal or supply an external clock signal at a lower frequency to get better frequency resolution for audio.

Amazon AD9833 from IC Station

IC Station AD9833 direct from IC Station

A swept frequency output can be used to measure amplifier and filter response. Or a white noise source and you can get sound cards that capture at 192ksps @ 24 bit, and software that can use that for a pretty good audio spectrum analyzer. Some include the ability to use one channel as an output to provide a swept sine wave, and the other as an input at the same time. Both your sound card and the software must support this.

This one looks impressive.

Quote
Cobracom - Waveguide
Cobracom Oscilloscope PC based

Oscilloscope, Realtime spectrum analyzer, Impedance meter, RLC bridge and signal generator for Windows. Is a Windows application that converts your PC into a powerful dual-trace signal analyzer (oscilloscope, FFT etc...) . Uses your PC sound card as an Analog-to-Digital a Converter to digitize any input waveform and as Digital-to-analog Converter for the signal generator. True 24 bit adc/dac 48K/96k/192k sampes/sec.
Cobracom Oscilloscope, PC based

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Steve Greenfield AE7HD


Tue Mar 28, 2017 12:04 pm
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Joined: Sun Aug 26, 2012 2:08 pm
Posts: 1048
Location: Lacey, WA USA
To reduce harmonic distortion of the sine wave, perhaps a tuneable lowpass filter that stays just above the output frequency.

I'll have to see how even the output of the AD9833 stays as frequency changes. The AD9850 and AD9851 have a problem with the output dropping as frequency rises, so people have designed gain control in to keep the signal level stable.

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Steve Greenfield AE7HD


Thu Mar 30, 2017 9:06 am
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