N3ZI DDS-2 VFO

By Ford-NØFP

I’ve been looking for a decent but simple signal source for some time.  After searching the web and losing interest a few times, I found N3ZI’s DDS-2 to be just the ticket for what I was hoping to find.  http://www.pongrance.com

I selected the optical encoder instead of the standard mechanical version Doug offers.  Assembly went well.  The TSSOP AD9834 proved to be a challenge since this was the first one I’ve tried to solder down.  8 pin versions yes.  20 pin?  Not-so-much.  The solder wick was the ticket to Paradise.  With solder wick the process took about 3 minutes.

Choosing a Hammond 7″x4″x2″ die cast box, layout was simple enough.  Although my initial goal is to have a bench signal source that operates like a VFO, the final project may well be some sort of QRP or SDR radio.  It turned out pretty nice if I might say so myself…

N0FP 1-30MHz VFV based on N3ZI DDS-2

I have the luxury of a vertical mill with DRO available.  Not your typical hamshack tool.  It proved invaluable to getting the lines straight, the holes punched accurately, and the troublesome LCD slot formed.  This is where most home-brew projects fall on their face.  Push buttons are simply not elegant.  And neither are the raw edges of a machined slot.  I set out to do better.

Using a 1/4″ end mill left rounded corners in the slot.  I debated having the LCD nest inside the slot, but that left the exposed frame of the LCD–equally ugly.  A finished commercial product would use some sort of plastic trim.  I decided to try something new.

LCD Trim using #12 black copper wire insulation

 Using an Xacto-knife with a new blade, I locked a short piece of #12 solid copper wire into the smooth jaw chuck of the mill.  Using the edge of the chuck as a guide for the knife was magic.  A slit along the length of the wire produce exactly the profile I needed to wrap the raw edges of the LCD slot.  It worked pretty good.  A very small diameter plastic tubing would be preferred.  But this was available, virtually free, and doesn’t look too bad.

An inside view of the final assembly shows that I have loads of room to be adding my next project, whatever that might be.

Inside View of final project

 Mounting the N3ZI DDS-2 to one side left me short on room.  The down push button was pretty close to the side.  So I shaved down some 1/4″ stand-offs to exactly 0.100″, which worked perfect.

Mounting the DDS-2 using 0.1" stand offs

I searched high-and-low on the internet, Digi-key, Mouser, Jameco, eBay, and could find no real nice looking push buttons.  If somebody discovers how to make a minibox mounted push button look good, let me know.

No project is ‘finished’ until the buttons are all labeled.  I use a clear tape label maker from Casio.  It was a great investment that has served me well.  The 8 batteries cost more than the label maker.  But the supplies are cheap and it does a fair job.  I decided to leave it natural finish.  Painting is such a hassle.  And the paint chips and scratches leaving a ‘worn’ look after heavy use.

Panel Labels using clear tape labels from a Casio labelmaker

 So there you have it.  I’m going to analyze the output in another post.  It seems surprisingly clean.  The 34MHz LP filter limits the normally 40MHz range, but it eliminates the mirror spurs up to about 20MHz I’m told.  It’s a function of the DDS methods.  Something I need to understand a bit better than I do right now.

10 Responses to “N3ZI DDS-2 VFO”

  1. Ford says:

    I just added audio derived AGC to the receiver and it made a HUGE improvement.

  2. Gary says:

    I use a small Delta jig (scroll) saw to cut square holes in Hammond cases.

    Make sure to put masking tape on top (protects from scratches from hold-down foot and install the blade to cut on down stroke. Don’t use the blades that cut on both up and down stroke – to much chatter and not a straight cut. Mark lines on masking tape. Cut very slow. A bit of finishing with a fine file is all that is needed.

    On my web site is a N3ZI frequency meter I recently built (under my vintage gear) and with a Hammond enclosure. Have built the vfo and integrating it into a Hammond enclosure the same way.

  3. admin says:

    Paul,
    A membrane switch is an interesting approach. I can’t quite visualize it though. At the link you provided, there is a data sheet. I note a 4 button switch. It looks like you cut a channel into the box and apply the membrane as an adhesive to the back of the panel. Is that correct? They are not particularly cheap. Have you used one of these or similar in a project that you could provide a link to?

    73

    Ford-N0FP

    • No I was just opondering the possiblities. I have a Ramsey Digital Signal generator which has membrance switches.

      You may look a appliances that have membrane switches, microwaves for example. The Digikey switch is a bit pricy. Mouser search engine looking for “membrane switch” shows some individual switch elements. With some sort of plastic cover they might work. My new coffee pot and our new glass top stove have membrane switches.

      I have a Norcal FCC1 DDS , it has stem switches that protrude through the panel. Thats where the idea of mounting the push button switches on a sub panel came from.

  4. digikey has a four function membrane switch see

    http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=360-2294-ND

    also search mouser and digikey for membrane switches.

    Paul k5wms

  5. admin says:

    Thanks for all the great ideas. I’m going to ponder the sub-plate approach for the next incarnation of whatever. I would like this to become a transceiver of some sort. I have an RX/TX 1.2W SDR radio that would fit into this enclosure. Using this as the basis for a fixed IF SDR might be a fun project. A good old fashioned superhet might be fun too.

    Ford-N0FP

  6. Jim says:

    Nice job, looks great. A possibility for the push button switches is to mount them on a sub plate and just drill a clearance holes in the front panel for the buttons

    Jim.

  7. Mike AA8W says:

    Looks good Ford. Those square holes are a pain!

  8. Paul Daulton k5wms says:

    About the push buttons, I would mount them on a plate behind the panel with just the tip of the buttons pushing through.

  9. Paul Daulton k5wms says:

    Thanks for posting the details of the LCD mounting. That looks really good. I will adapt that to a couple of my projecs.

    I have N3zi 20 merter beacon xtal controlled rec as my next project, then will adapt it to 30m qrss and wspr frequency.

    Nice job.
    Paul

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