What Makes A Good Antenna?

It sometimes seems as though antennas and RF design are portrayed as something of a Black Art, the exclusive preserve of an initiated group of RF mystics and beyond the reach of mere mortals. In fact though they have their difficult moments it’s possible to gain an understanding of the topic, and making that start is the subject of a video from [Andreas Spiess]. Entitled “How To Build A Good Antenna”, it uses the design and set-up of a simple quarter-wave groundplane antenna as a handle to introduce the viewer to the key topics.

What makes this video a good one is its focus on the practical rather than the theoretical. We get advice on connectors and antenna materials, and we’re introduced to the maths through online calculators rather than extensive formulae. Of course the full calculations are there to be learned by those with an interest, but for many constructors they can be somewhat daunting. We’re shown a NanoVNA as a useful tool in the antenna builder’s arsenal, one which gives a revolutionary window on performance compared to the trial-and-error of previous times. Even the ground plane gets the treatment, with its effect on impedance and gain explored and the emergence of its angle as a crucial factor in performance. We think this approach does an effective job of breaking the mystique surrounding antennas, and we hope it will encourage viewers to experiment further.

If your appetite has been whetted, how about taking a look at a Nano VNA in action?

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Tracking Satellites: The Nitty Gritty Details

If you want to listen to satellites, you have to be able to track them as they pass over the sky. When I first started tracking amateur satellites, computing the satellite’s location in the sky was a part of the challenge. Nowadays, that’s trivial. What’s left over are all the extremely important real-world details.  Let’s take a look at a typical ham satellite tracking setup and see how it all ties together.

Rotators for Steering

The popularity of robotics, 3D printing, and CNC machines has resulted in a deluge of affordable electric motors and drivers. It’s hard to imagine that an electric motor for rotating an antenna would be anything special, but in fact, antenna rotators are non-trivial engineering designs. Most of the challenges are mechanical, not electrical — the antennas that they drive can be huge, have significant wind loading and rotational inertial, and just downright weigh a lot. A rotator design has to consider bearings, weather exposure, all kinds of loads, not just rotational. And usually a brake is required to keep the antenna pointed in windy conditions.

There’s been a 70-some year history of these mechanisms from back in the 1950s when Cornell Dubilier Electronics, the company you know as a capcacitor manufacturer, began making these rotators for television antennas in the 1950s. I was a little surprised to see that the rotator systems you can buy today are not very different from the ones we used in the 1980s, other than improved electronic controls. Continue reading “Tracking Satellites: The Nitty Gritty Details”

Ham Antennas From MIT

Dealing with an antenna is one of those topics we never feel like we know enough about. MIT had a live stream of [Dr. Kiersten Kerby-Patel] discussing antennas in a talk, sponsored by the ham radio club on campus. You can see the recording below.

The main assertion of the presentation is that everything is a dipole unless it is a loop. Although the professor probably deals with antennas at an extremely high theoretical level, she did a great job of keeping it aimed at ham radio operators.

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A 60 GHz Phased Array

Our friend [Hunter Scott] gave a talk at a past Supercon about phased array antennas. He mentioned he was looking for collaborators to create an antenna with the SiBeam SB9210 chip. This is a specialized chip for WirelessHD, a more or less failed video streaming protocol, and it’s essentially an entire 60 GHz phased array on a chip with both transmit and receive capabilities. For $15, it seems like quite the bargain, and [Hunter] still wants to put the device to work.

The downside is that Lattice bought SiBeam and killed this chip — not surprising considering WirelessHD never really took off. However, [Hunter] says the chip was in some old smart TVs and laptops. If you can find replacement boards for those devices on the surplus market, you can get the chip and the supporting circuitry for a song.

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The Power Of Directional Antennas

AM broadcasting had a big problem, but usually only at night. During the day the AM signals had limited range, but at night they could travel across the country. With simple wire antennas, any two stations on the same frequency would interfere with each other. Because of this, the FCC required most radio stations to shut down or reduce power at night leaving just a handful of “clear channel” stations for nighttime programming. However, creating directional antennas allowed more stations to share channels and that’s the subject of a recent post by [John Schneider].

When it comes to antennas, ham radio operators often think bigger is better. After all, hams typically want to work stations far away, not some specific location. That’s not true in the commercial world, though. The big breakthrough that led to for example cell phones was the realization that making smaller antennas with lower power at higher frequencies would allow for reuse of channels. In those areas the focus is on making cells smaller and smaller to accommodate more people. You can think of AM broadcasting as using the same idea, except with relatively large cells.

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Justin McAllister’s Simple, Post-Apocalypse-Friendly Antennas

Watch Justin McAllister’s presentation on simple antennas suitable for a zombie apocalypse and two things will happen: you’ll be reminded that everything antennas do is amazing, and their reputation for being a black magic art will fade dramatically. Justin really knows his stuff; there is no dangle-a-wire-and-hope-for-the-best in his examples. He demonstrates that it’s possible to communicate over remarkable distances with nothing more than an off-the-shelf radio, battery pack, and an antenna of simple design.

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Ground Penetrating Radar For The Masses

Radar is a useful tool with familiar uses such as detecting aircraft and observing weather. It also has some less known applications, such as a technology known as ground-penetrating radar (GPR). Despite the difficulty of sending and receiving radio waves through solid objects, with the right equipment it’s possible to build a radar that works underground as well.

GPR is used often for detecting underground utilities, but also has applications in other fields such as archaeology and geology. For those people in these fields, a less expensive GPR was the priority of a group presenting at a 2017 National Institute of Telecommunications of Poland conference (pdf warning). The presentation goes into specific detail on how to build a GPR for around €600, much less than commercial offerings.

The presentation begins by highlighting the basics of GPR, then details the hardware bill of materials for the transmitting circuit, receiving circuit, and the DC power supplies. It also details the theory behind the software needed to get the circuit running properly, and has code as well. The processing is done on a 32-bit Mbed platform, and the rest of the GPR is built with easy-to-source components as well.

It’s always good to see useful hardware projects that bring costs of traditionally expensive equipment down to the grasp of average people. Even traditional radar systems are now available for hundreds of dollars, and we’ve even seen attempts at other GPR systems before as well.

Thanks to [Stefan] for the tip!