In this Instructable I'll show you how I built a low-cost antenna analyser which can measure an antenna and display its VSWR over any or all of the HF frequency bands. It will find the minimum VSWR and corresponding frequency for each band but also will display a realtime VSWR for a user-selected frequency to facilitate antenna adjustment. It also has a USB port on the back for outputting frequency and VSWR data, to allow graph-plotting on a PC. The USB port can also be used to reflash the firmware if needed.
I recently got into amateur radio (because I liked the idea of peer-to-peer communication over huge distances without infrastructure) and rapidly made the following observations:
1. All of the worldwide communications that interested me take place on the HF bands (3-30 MHz)
2. HF transceivers are very expensive and will break if you don't drive them into a reasonably well-matched antenna
3. You are generally expected to rig up your own HF antenna from bits of wire strung across the garden (unless you want to spend even more money than you spent in 2).
4. Your antenna might be a bad match but you won't know till you try it.
Now a purist would probably say that one should first test the antenna on very low power at the frequency of interest and check the VSWR on the rig's meter to assess the quality of the match. I don't really have the time to muck about with that sort of thing for every frequency I might want to use. What I really wanted was an antenna analyser. These devices can test the quality of the antenna match at any frequency over the HF bands. Unfortunately they are also very expensive, so I set about considering whether I could make my own. I stumbled upon the excellent work carried out by K6BEZ (see http://www.hamstack.com/project_antenna_analyzer.html), who investigated the use of an Arduino to control a cheap direct digital synthesiser module (DDS). He soon abandoned the Arduino on cost grounds, preferring to use a PIC. Well, in 2017 you can buy an Arduino Nano for about £3.50, so I thought it was time to revisit his work, pick up where he left off and see what I could come up with.
Update - as several people have asked about schematics, the fundamental Arduino / DDS / VSWR bridge circuit is largely unaltered from K6BEZ's original work. Please check out the above URL for his original schematic on which I based this project. I've added an encoder, an OLED screen and fully developed firmware to make for an effortless user experience.
You will need the following items. Most of them can be obtained cheaply from Ebay. The most expensive single item was the box, at close on £10! It might be possible to substitute some items (I used 47 Rs instead of 50 Rs, for example). The diodes were rather unusual (I had to buy 5 off from Italy) and would be worth substituting for more readily available items if you know what you are doing.
You'll also need a soldering iron and electronics tools. A 3D printer and a pillar drill are helpful for the enclosure, although if you wanted you could probably assemble the whole thing on the stripboard and not bother with a box.
Naturally you undertake this work and exploit the results generated at your own risk.