Author Topic: 30 MHZ ad9850 DDS Signal Generator in 12$  (Read 55669 times)

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Offline Ranger14

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Re: 30 MHZ ad9850 DDS Signal Generator in 12$
« Reply #125 on: February 08, 2016, 07:18:24 pm »
Do you guys think this is worth building and does it have good enough accuracy??
 

Offline retrolefty

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Re: 30 MHZ ad9850 DDS Signal Generator in 12$
« Reply #126 on: February 08, 2016, 09:11:14 pm »
Do you guys think this is worth building and does it have good enough accuracy??

 Well 'good enough' is not a useful unit of measurement.  :-DMM

However I built a similar device using the AD9850 used as the VFO LO for a ham 7MHz CW receiver. Worked great, heard no distortion, and very stable frequency control. I amplified the output using a MMIC chip to drive a double balanced diode mixer. So lots of capability for very little $, what's not to love?

 
 

Online Mechatrommer

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Re: 30 MHZ ad9850 DDS Signal Generator in 12$
« Reply #127 on: February 08, 2016, 09:23:53 pm »
The AD9850 good for me  ;).
NewFile6.jpg
congratulation for reading the signal in average mode...
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Offline AustinTxBob

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Re: 30 MHZ ad9850 DDS Signal Generator in 12$
« Reply #128 on: February 09, 2016, 05:04:44 pm »
The AD9850 good for me  ;).
NewFile6.jpg
congratulation for reading the signal in average mode...

Harsh?  Why not explain what is wrong and why that may not be the best setting?  Us newbies might benefit more from that.

I did get a much cleaner reading on mine by swapping out the ground lead to the spring.  There was another thread talking about this.  Thanks to whomever posted that! (I wish I saved the link.)
 

Online Mechatrommer

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Re: 30 MHZ ad9850 DDS Signal Generator in 12$
« Reply #129 on: February 09, 2016, 09:35:54 pm »
Harsh?  Why not explain what is wrong
no i'm trying to be gentle actually, since most newcomers will get hot when told the truth and they will come with their machine gun theory book. look, my AD9850...

picture 1) very nice!
picture 2) so so
picture 3) well?

bear in mind this is sampled 25 points per cycle (40MHz @ 1GSps)
picture 4) how a theoritical 25pts sine should looks like.

conclusion: "average" will closely resemble perfect sine. "single capture" (picture 3) is the truth. if we want talk sweet and sugar, we show "average", if we want to talk the truth grain and salt, show "single capture", "average" is nice, but not truth. and lastly... use 1X attenuation 50 ohm Z coax with 50 ohm termination at the scope end when testing, thats the de-facto standard way... google it its too long, fwiw..

picture 5) when superimposed theory and the truth... fwiw..
« Last Edit: February 09, 2016, 09:55:13 pm by Mechatrommer »
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Offline AustinTxBob

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Re: 30 MHZ ad9850 DDS Signal Generator in 12$
« Reply #130 on: February 10, 2016, 04:44:41 am »
and lastly... use 1X attenuation 50 ohm Z coax with 50 ohm termination at the scope end when testing, thats the de-facto standard way... google it its too long, fwiw..

Googling that now.  Thanks!  As you can see from the pics I posted, I took a single instead of the OP's average.  Also I was just probing directly on the board with no termination. 

I'm putting it into an antenna analyzer right now so we'll see what it looks like when it is seeing 50 ohms.
 


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