Antenna Basics by Whiteboard

Like a lot of people, [Bruce] likes radio controlled (RC) vehicles. In fact, many people get started in electronics motivated by their interest in RC. Maybe that’s why [Bruce] did a video about antenna basics where he spends a little more than a half hour discussing antennas. You can see the video below.

[Bruce] avoids any complex math and focuses more on intuition about antennas, which we like. Why does it matter that antennas are cut to a certain length? [Bruce] explains it using a swing and a grandfather clock as an analogy. Why do some antennas have gain? Why is polarization important? [Bruce] covers all of this and more. There’s even a simple experiment you can do with a meter and a magnet that he demonstrates.

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The components are INSIDE the circuit board

Through-hole assembly means bending leads on components and putting the leads through holes in the circuit board, then soldering them in place, and trimming the wires. That took up too much space and assembly time and labor, so the next step was surface mount, in which components are placed on top of the circuit board and then solder paste melts and solders the parts together. This made assembly much faster and cheaper and smaller.

Now we have embedded components, where in order to save even more, the components are embedded inside the circuit board itself. While this is not yet a technology that is available (or probably even desirable) for the Hackaday community, reading about it made my “holy cow!” hairs tingle, so here’s more on a new technology that has recently reached an availability level that more and more companies are finding acceptable, and a bit on some usable design techniques for saving space and components.

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The Poynting Vector Antenna

Radio amateurs are inventive people, and though not all of them choose to follow it there is a healthy culture of buildng radio equipment among them. In particular the field of antennas is where you’ll find a lot of their work, because the barrier to entry can be as low as the cost of a reel of wire.

Over the years a number of innovative antenna designs have come from radio amateurs’ experimentation, and it’s one of the more recent we’d like to share with you today following a [Southgate ARC] story about a book describing its theory (Here’s an Amazon link to the book itself). The Poynting Vector antenna has been one of those novel designs on the fringes for a while now, it has been variously described as the “Super-T”, or the “flute”. Its party piece is tiny dimensions, a fraction of the size of a conventional dipole, and it achieves that by the interaction between a magnetic field across the plates of a capacitor in a tuned circuit and the electric field between a very short pair of dipole radiators. The trade-off is that it has an extremely high Q and thus a narrow bandwidth, and since its feeder can become part of its resonant circuit it is notoriously difficult to match to a transmitter. [Alan MacDonald, VE3TET] and [Paul Birke, VE3PVB] have a detailed page on the development of their Poynting antenna which takes the reader through the details of its theory and the development of their practical version.

In the roof space above the room in which this is being written there hangs a traditional dipole for the 20m amateur band. Though it is a very effective antenna given that it is made from a couple of pieces of wire and a ferrite core it takes most of the length of the space, and as we’re sure Hackaday readers with callsigns will agree a relatively tiny alternative is always very welcome.

If antennas are a mystery to you then we’d suggest you read an introduction to antenna basics to get you started.

Visualization of a Phased Array Antenna System

Phased array antenna systems are at the cusp of ubiquity. We now see Multiple-Input Multiple-Output (MIMO) antenna systems on WiFi routers. Soon phased array weather radar systems will help to predict the weather and keep air travel safe, and phased array base stations will be the backbone of 5G which is the next generation of wireless data communication.  But what is a phased array antenna system?  How do they work?  With the help of 1024 LEDs we’ll show you.

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Automatic Antenna Tuner

Automatic Antenna Tuner

To get the best power transfer into an antenna, tuning is required. This process uses a load to match the transmission line to the antenna, which controls the standing wave ratio (SWR).

[k3ng] built his own automatic antenna tuner. First, it measures the SWR of the line by using a tandem match coupler. This device allows the forward and reflected signals on the line to be extracted. They are buffered and fed into an Arduino for sampling. Using this data, the device can calculate the SWR. The RF signal is also divided and sampled to measure frequency.

To automate tuning, an Arduino switches a bank of capacitors and inductors in and out of the circuit. By varying the load, it can find the ideal matching for the given antenna and frequency. Once it does, the settings are stored in EEPROM so that they can be recalled later.

After the break, check out a video of the tuner clicking its relays and matching a load.

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Making a 9GHz doppler radar

[Kalle] is currently building an FMCW radar, but as he doesn’t have all the parts finished he decided to build a 9GHZ doppler radar in the mean time. The H-plane horn antennas were made from brass sheet and soldered together. [Kalle] checked the matching between the emitter and the antenna by inserting a directional coupler between the two and measuring the intensity of the reflected signal (approximated return loss). At 9Ghz, the Doppler shift for a 1 meter per second speed is about 30Hz so he connected the radar’s output signal to his soundcard.

A quick explanation of the Doppler effect that a radar uses: if you send an RF signal at a given frequency to a moving target, the reflected signal’s frequency will be shifted. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from an observer. The received frequency is higher (compared to the emitted frequency) during the approach, it is identical at the instant of passing by, and it is lower during the recession. Hackaday featured plenty of projects using this effect: a small doppler motion sensor, gesture control using doppler shift, hacking an old radar gun

Ask Hackaday: Building nano scale antennas

As an RF engineering student, [Camerin] is usually tasked with pointless yet educational endeavors by his advisor and professors. Most of the time (we hope) he sees the task through and ends up pulling something out of his hat, but a few days ago a professor dropped a bombshell on him. After reading this article on nano scale antenna fabrication, a professor asked [Camerin] if it was possible to build a 3D inkjet printer with a ludicrous amount of accuracy and precision.

The full article, Conformal Printing of Electrically Small Antennas on Three-Dimensional Surfaces, was recently published in Advanced Materials and is available via Google Scholar. The jist of the article is that three-dimensional antennas printed on a sphere approach the physical limits of how good an antenna can be. To test out these small, spherical antennas, the authors of the paper built an extremely high-precision 3D inkjet printer that draws antenna traces on a glass sphere with conductive ink.

The positional accuracy of this printer is 50 nanometers, or about half the size of an HIV virus. The conductive silver ink is delivered by a nozzle with a diameter of 100 to 30 µm and prints onto a glass sphere about 6 mm in diameter. This is a level of precision that companies and research institutions pay top dollar for, so we’re left wondering how the authors built this thing.

We’re turning this question over to the astute readers of Hackaday: how exactly would you build a 3D inkjet printer with this much accuracy and precision? Would it even need to be that precise? Post your answer in the comments.