If you are a hacker, you might consider ham radio operators as innovative. Most people, however, just see them as cheap. So it is no surprise that hams like [jmharvey] will build an antenna analyzer from a DDS module and an Arduino instead of dropping a few hundred dollars on a commercial unit. As he points out, you probably only need an analyzer for a day or two while you set up an antenna. Unless you are a big time antenna builder, the unit will then sit idle on the shelf (or will wind up on loan to hams even cheaper than you are).
The design is rooted in another proven design, but changed to take advantage of parts he happened to have on hand. Although the build is on a universal circuit board, [jmharvey] used Eagle to lay out the circuit as though it were a PCB. Since placement can be important with an RF circuit, this isn’t a bad idea. It’s always easier to move stuff around on the screen than on the perf board.
Since this is a no frills, unit, you are expected to grab the output from the Arduino and manually put it in a spreadsheet to plot the results. There is another version of the Arduino code that drives an OLED screen, although you still need a PC to kick the process off. One interesting feature of the Arduino code is how it deals with the nonlinear nature of the diodes used in the circuit. After plotting the values with known loads, [jmharvey] broke the diode operation into three regions and used different equations for each region. Even so, he warns that readings higher than 1:1 VSWR are only accurate to 10% or 20% – still good enough for ham shack use.
If you want an antenna analyzer for $40 (or less, if you have a good stock of parts) this looks like a worthwhile project. If, however, you want to repurpose it to Rickroll your neighbor’s AM radio, you might want to go with the commercial unit.
Click past the break to see the analyzer in action.
Continue reading “$40 Antenna Analyzer with Arduino and AD9850”
A while back, [m0xpd] picked up an unbearably cheap AD9850 DDS module from ebay. He turned this in to a Raspberry Pi-powered radio beacon, but like so many builds that grace our pages, the trolls didn’t like using such an overpowered computer for such a simple device. To keep those trolls quiet, [m0xpd] is back again, this time using the AD9850 DDS module as a radio beacon with an Arduino.
The previous incarnation of this build used a Raspberry Pi, and as a consequence needed a level converter. This was thrown out as [m0xpd]’s own Arduino clone, the WOTDUINO – pronounced, ‘what do I know’ – is able to handle the 5 Volt IO of the AD9850.
In addition to fabbing a shield for the DDS module, [m0xpd] also constructed a transmitter shield to amplify the signal and allow the ‘duino to key out a few simple messages. It’s a quite capable device – one of [m0xpd]’s messages traveled from merry olde England to Arizona, his best ever westward distance.
[m0xpd] got his hands on an inexpensive AD9850 DDS Module from eBay but needed a way to control it. He took inspiration from the projects that used a PIC microcontroller, but decided to add his own twist by using a Raspberry Pi to build a multi-mode beacon transmitter.
At the center of this breadboarded circuit lies the green AD9850 module. To its left is a level converter he built to get the 3.3V levels from the RPi board to work with the rest of the 5V hardware. The signal then feeds into a QRP amplifier and a low pass filter.
He didn’t start from square one when it came time to write the code for the RPi. Instead he grabbed an Arduino sketch for the very same DDS and ported it over to Python. The first test signal was his call sign sent in Morse code at QRSS speeds. But he also managed to get Hellschreiber messages working, making it a multiple-mode device.
[via Solder Smoke]