Posted: 4/16/2014 5:10:29 PM EDT
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I had been playing with the Arduino micro-controller a bit and ran across some projects using that plus some low cost DDS boards to build a DIY antenna analyzer that looked interesting. Since I'm on light duty for a few months following lumbar surgery, it looked like a good low-impact activity. I don't have any illusions that the final product will be anywhere near the equivilant of a real commercial product or even a decent kit, but it should be fun and educational.
This is still a work in progress, at this point. Pretty much just the UI framework is running, but I should be able to start trying out the fun stuff fairly soon now. I am going to use the one platform for a SWR/PWR meter build, a frequency generator, and hopefully an HF band antenna analyzer. I picked up a couple of the sub $10 AD9850 DDS breakout boards, some ATMega328P chips with Arduino compatible optiboot bootloaders already onboard. and supporting items to clone my Arduino so it would not be at risk. I picked up an SWR bridge kit, but may end up using a resistor network for the analyzer build... 
DDS boards The first thing was breadboarding the DIY version of an Arduino Uno and testing DDS boards to see if I could talk to them. It turned out to be pretty easy just using example code readily available online. The old Phillips scope cooperated long enough to see the generated output (after a while the internal trigger gets flakey). 
DDS output controlled by Arduino (bad cell phone pic) I moved breadboard circuits over to some project board and started looking for a cheap enclosure to build on. I ended up with a dollar store sandwich box, that got lined with aluminum tape. I mounted a 20 char x 4 line LCD, a rotary encoder and a couple of momentary buttons for controls on the lid, securing things with hot glue. 
The bottom got a power jack, on/off switch and a couple of BNC connectors. 
It also got a small piece of project board with a 3.3v & 5v power supply that can run from a 8v - 15v source, and a wide band HF SWR bridge built from a kitsandparts.com kit. The next thing was to work on some appropriate control code for the user interface issues. This was the first original work I've done with the Arduino IDE, but I used to do a bit of coding before I retired, and picking up a new language/environment isn't a big deal. I wanted something that would potentially support multiple project approaches, so I built code for displaying and traversing a simple menu environment. I used a couple of pinchange interrupts to catch button presses, but stayed with a simple looped watch on the encoder for movements within the menu. 
The DIY Arduino Uno clone is pretty small. I currently use an $8 FTDI breakout board for programming & serial out that plugs into a header on the project board. I built a DIP style adapter for the DDS board and it is on another small piece of project board. Everything is being done modular so I can swap out what doesn't work out. 
FWIW, the red/black color coordination was coincidental junk box finds. The rotary encoder knob is a chopped off wire-nut. I'll update as things get more interesting Nick |
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Just a quick update...
I'm still playing with this, but have had a problem getting the expected fwd vs ref values when testing with open vs 50 ohm termination, etc. or sweeping on an antenna. I tried two different wheatstone bridge approaches plus a kitsandparts "universal swr" grp kit but never saw the degree of differentiation you would expect -- even when processing the values through an AD8307 prior to the Arduino. I recently picked up a low power (< 4 watt max) dual directional coupler good for 0.2- 250 Mhz and will give that a try next before resorting to adding an amp to the AD9850 output. I can generally hack my way through digital/TTL electronics but sometimes feel like a babe in the woods with RF circuits. On the plus side I was successful with wiring up SD card read/write capability so the working version will be able to record data points from a sweep for later charting without having to be tethered to a pc/laptop while running... Nick |