You don’t have to be an amateur radio operator to meddle with radio frequencies. Many applications today operate on frequencies once thought of as purely radio. For example, switch mode power supplies (SMPS), ultra-sound measuring and alarms, and of some interest to us, component testing and analysis of inductive and capacitive circuits.
The board described here is not a complete instrument, in that it requires a computer, or an Arduino and LCD or such, as the HMI (human machine interface).
We have used various antenna analysers, and instruments that can measure RF SWR and Impedance. The instruments are often old, and all analogue; require manually setting the band and frequency, but at least one displays the frequency digitally.
Of course, the RigExpert series of antenna analysers do a whole lot more with frequency versus SWR, impedance plots and even Smith charts, on their small but clear colour LCD display. Essentially, the AA-30 Zero is the board that creates the magic inside, so BYO display!
The PCB is an Arduino shield format with a SMA coaxial connection on one end, onto which you plug an antenna, external circuit, component, or probe.
To begin with, the Zero generates a frequency from 60kHz to 30MHz, which can be set to a fixed frequency, or set to scan the whole band if you so desire. By itself, it is a great value frequency generator.
The signal generated by the Zero passes through a measuring circuit to the socket, so software can actually measure the impedance of whatever is attached, at the frequency set, or across a band. You can make yourself a HF CB antenna, shortwave antenna, or AM radio antenna, or design filters or other antennas, and test them to make sure they measure up.
The 70mm x 53mm shield fits the Arduino as a UART to USB bridge; or the Arduino can run the show and pass the measurements to an LCD display. Alternatively, the Zero works off a USB breakout adapter, to operate directly from a Windows box, using free software that is available online.
The RigExpert team built a range of antenna analyser products in the Ukraine, with models of handheld instruments from a few kHz through to 1.4GHz, and a special single band instrument (IT24) for 2.4GHz including WiFi. Have you ever wondered whether your WiFi network antenna was working? Maybe you have wanted to build a “super” WiFi antenna, and test it?
Our sample arrived in rural Queensland from the store in Albany Creek, Brisbane in a couple of days. It was well protected in a box with bubble wrap, and pretty much ready to go out of the box. You decide whether you want a full set of Arduino pins, or just a few connections, but the strips of pins are supplied for you. A quick solder job, download and install the “AntScope V2” software, (Windows only!) and you are away. An alternative is to drive the PCB using your own code, using simple commands and the Arduino serial link.
The PCB is simple and suits integration into your own hardware, including an automatic antenna tuner, or large screen display. It is well made with sectionalised blocks clearly marked on the overlay. The soldering is easily completed, even if you're just a beginner! The design packs a lot of functionality into a single shield, and has a range of uses exceeding the intended design.
The commands are also simple (e.g., “ver” returns the version of your PCB and firmware version; “fq27125000” will put you on channel 11 of CB radio; “sw1000000” will scan from 26.625MHz to 27.625MHz; and “frx10” will return values of resistance and reactance for every 100kHz). Of course, every command requires a carriage return, to cause the serial link to pass the command.
There’s just one feature we would like to see, and that would be the addition of an onboard USB socket and USB-UART chip, to make the PCB a standalone device; albeit for operation from a parent computer. It takes a firm place, piggy-backed on a Mega2560 with a colour LCD touch screen.
There’s not much out there in the market to compare it to, as nobody makes quite the same power available in such a small package. Comparing it to a $600 antenna analyser doesn’t quite seem fair, but it would hold its head up nonetheless. At the other end is a $6.95 DDS (Direct Digital Synthesis) plug-in that has no impedance measuring at all.
There are other kits available, but nothing as complete or as reliable, since the ICs are all very small and require SMD soldering skills, which can often be a challenge.
With great features in a tidy unit, it compares well with other technology available. It's easy to use, and will be at home with all of the test equipment in your kit.
The Zero is an instrument very suitable to amateur radio, and other hobbies, and very flexible in that you can program it suit to your specific tasks.
The RigExpert AA-30 is available in Australia from RF-Solutions for $125, and available for delivery by normal mail.
Grab it online from RFSolutions:
- RigExpert AA-30 $125