OOPS! Why the AD9850 DDS Boards are So Inexpensive

N3ZI has a very plausible explanation for the low price (about 9 bucks!):

My guess is that this is a liquidation due to a design build error, since they are being sold for a price of about 1/2 the price of the DDS chip alone. The modules are assembled and tested. The design error I noticed is that the wrong output filter is used. These boards use the 9850 running at 125MHz. A 125MHz DDS should have a 50MHz LPF, but it seems that these modules have the 75MHz LPF the chip maker recommends for the AD9851 running at 180MHz. My guess is, someone just copied the wrong filter from the wrong data sheet, and it wasn't caught until they went into production.
But for amateur radio applications they work fine up to about 40MHz. You can push them to 50MHz by adding a correcting filter, which is included in my controller PCB, but the output level is low in the 40-50MHz range.

N3ZI continues to offer some really interesting microcontroller products.  He has a controller board that allows you to simultaneously control TWO AD9850 boards.  This might be exactly what we need when we have a separate receiver and transmitter with different intermediate frequencies: Set up one board with the VFO freq for the receiver and the other for the transmitter with the resulting operating freq displayed on the LCD.  Viola! No more "Spot" or "net" and zero-beat by ear! (But I may be one of the last people on the planet still doing this!)   

N3ZI's site:  http://www.pongrance.com/

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

R-390A and Homebrew TX put in Transceive Mode (VIDEO)

N8ZRY has a very nice video on his recent adventures with the legendary R-390A receiver (want one!) and his homebrew 20 meter SSB transmitter.  He manages to essentially put the receiver and transmitter into "transceiver" mode.  Very nice.  I wonder if he had previously used the old standard "spot" or "net" "zero beat by ear" method?  This video has me thinking about ways to bring my many separate receivers and transmitters closer together. The problem is that they all use different IF frequencies (the crystal filters are at different frequencies).  But using my Arduino-based DDS VFO, I guess it wouldn't be too difficult to program the thing to generate one VFO freq for transmit, and a different VFO freq on receive, in effect putting the transmitter and receiver on the same frequency. 

Both the R-390A and the homebrew transmitter look great.   Thanks Greg!


Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

Dutch Knack During WWII

 

 

There is a very nice article on the MAKE blog this morning: 
http://blog.makezine.com/2013/06/06/an-early-maker-story-from-holland/
 
Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

Quote of the Day: On Tinkering

Finally, some justification for my "build first, design later" method:

"Contraptions, machines, wildly mismatched objects working in harmony -- this is the stuff of tinkering.  Tinkering is, at its most basic, a process that marries play and inquiry."

from www.exploratorium.edu/tinkering   Quoted in Massimo Banzi's book "Getting Started with Arduino."

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

Alan Yates, VK2ZAY, is back in the knack!

I was getting kind of worried.  I hadn't seen any new articles on Alan's excellent web site.  But on my last visit I learned that he has moved to Seattle and is going to Maker Faires:  http://www.vk2zay.net/article/268

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

Save 20% on Knack Books

Codeword: GLOW.   Very appropriate for Grayson's Thermatron book: 



http://www.lulu.com/shop/grayson-evans/hollow-state-design/paperback/product-20987562.html


And also for mine (tubes, QRP fireflies and all that):



http://www.lulu.com/spotlight/soldersmoke

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

1-29 MHz In One Small Box

 

This weekend I put the Arduino/AD9850 Direct Digital Synthesis device into a box this weekend.  It is sort of evolving into a general purpose HF signal generator and/or VFO.  It is really kind of neat that this little collection of boards can generate RF across that range, with accurate digital readout.  Thanks again to Richard Visokey, AD7C, for the circuit and the code.  As you can see, my cabinet making skills will never land me a job on the Discovery Channel,  but I'm kind of pleased with the box.  I picked up the wood panels from a hobby/craft shop. 



 

 

I left a lot of space in the box.  I envision an amplifier taking the output from its current .4 milliwatts up to around 10 milliwatts, followed by step attenuators (pads).

 

Here is the other end.  Of course, I could have just taken the ATMega chip out and avoided putting the whole Arduino board inside the box, but I'll leave that exciting digital adventure for a future project.


Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20