You start with the capacitor shaft turned all the way to the high-capacitance end of motion, i.e., the low-frequency end. The LCD is showing the initial inputs used to calibrate the relationship between stepper motor position and tuned frequency. With all of the pre-fab components, this is just about all of the wiring that I will need for the entire project. The stepper motor will be powered by the 13.8-volt power supply for my transceiver, but at the moment is powered by a benchtop power supply. The AA30.ZERO is hooked up to a 6-foot STL, and the white-sheathed 4-wire cable runs power and signals to the stepper motor. A simple 16-key keypad for control and a 20×4 LCD completes the ensemble. The microstep driver for the stepper motor is on the left. The AA30.ZERO is in the top center, mounted on an Arduino UNO. But, this also makes it ideal for designing a stand-alone tuning system, which is what I’m doing. If you just want to use the Arduino as a bridge between the ZERO and your computer, there is software available to read and plot the analyzer data. It’s under 100 USD, and configured so it can be used as an Arduino shield. However, I discovered that RigExpert sells an antenna analyzer on a circuit board, the AA-30.ZERO. Plus, there were some things I wanted to do differently, as well as try to simplify the system.Ĭontrolling the capacitor using an Arduino and a stepper motor turns out not to be too difficult, but would still requiring actually tuning by hand based on my computer-controlled miniVNA Pro. I’ve known about that for a year or so, but without simply copying all of his work, there’s no way I was going to be able to reproduce that within a reasonable amount of time (and even that might be a challenge the hardware was intimidating enough that I’ve never even looked at the software!). Loftur Jonasson has posted a great design for such a thing. By it’s very nature, an STL has a very narrow tuning bandwidth (“high Q”), which is the big compromise you have to make to have a usable antenna that is much smaller than the wavelength you are using. I have been using “regular” DC motors for my loops, but that requires a separate antenna analyzer and a tedious manual process of fine-tuning the capacitor everytime I change frequencies. Not long after I started my video series on small-transmitting loops (STLs, or “magnetic loop”), I got distracted by the thought of using a stepper motor for precise control of the variable capacitor.
0 Comments
Leave a Reply. |