Tuesday, May 17, 2016

AD9850 DDS VFO

You know when you have a project where you thought "I'll just throw some things together and see how it goes" and it works amazingly well on the first try?

I guess there is a first time for everything...

In any case, I got an AD9850 in the mail the other day, and I wanted to have a go at playing with it.  I found a bunch of write-ups of people doing this, but this one looked really well thought out.

I started out trying parts of his program, just to make sure I (a) understood it and (b) wired things right.  I started with the lcd and got hello world working.  Then I took his code and commented out most things to get the rotary encoder part working.  Then I wired up the whole thing and loaded up his code.  The only issue I had was that the for me, the include for the rotary code needed it spelled "Rotary.h" instead of lower case r.



After playing around with the step settings, etc, as he suggests in his writeup - I immediately got treated with a beautiful sine wave!

Encouraged, I started pulling the VFO components from my DC receiver I put together the other day.  I put the output of the DDS into pin 6 of the NE602 via a 10pF cap.  You can see the messy result here:


I excitedly turned on everything and attached a long wire to the antenna...  and I immediately heard code!!  The receiver is definitely crunchy (not enclosed, no filters, questionable antenna, etc), but it is super easy to tune with the digital VFO.  So excited!!

I'll probably play with this it in this form for a few days, but already trying to decide what to do next.  Thoughts include a bpf for the front end, some sort of narrow cw filter, and a simple agc circuit.  Oh, and maybe getting it off of a breadboard and into some sort of actual enclosure.

I want to thank Jan Ciger for sharing his awesome project!

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