antenna

253 Articles

Antenna Measurement In Theory And Practice

December 6, 2024 by 9 Comments

If you want to analyze an antenna, you can use simulation software or you can build an antenna and make measurements. [All Electroncs Channel] does both and show you how you can do it, too, in the video below.

The antenna in question is a loop antenna. He uses a professional VNA (Vector Network Analyzer) but you could get away with a hobby-grade VNA, too. The software for simulation is 4NEC2.

The VNA shows the electrical characteristics of the antenna, which is one of the things you can pull from the simulation software. You can also get a lot of other information. You’d need to use a field strength meter or something similar to get some of the other information in the real world.

The antenna simulation software is a powerful engine and 4NEC2 gives you an easy way to use it with a GUI. You can see all the graphs and plots easily, too. Unfortunately, it is Windows software, but we hear it will run under Wine.

The practical measurement is a little different from the simulation, often because the simulation is perfect and the real antenna has non-ideal elements. [Grégory] points out that changing simulation parameters is a great way to develop intuition about — in this case — antennas.

Want to dive into antennas? We can help with that. Or, you can start with a simple explanation.

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$40 Ham Antenna Works Six Bands

November 23, 2024 by 14 Comments

[My Ham Radio Journey] wanted to see if a “common person” (in his words) could build an effective vertical ham radio antenna. If you look at the video below, the answer is apparently yes.

He started with a 24-foot fishing rod and a roll of 22 gauge wire. The height of the antenna wire is just over 20 feet long and he has several ground radials, as you might expect for a vertical antenna.

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Schooling ChatGPT On Antenna Theory Misconceptions

November 17, 2024 by 39 Comments

We’re not very far into the AI revolution at this point, but we’re far enough to know not to trust AI implicitly. If you accept what ChatGPT or any of the other AI chatbots have to say at face value, you might just embarrass yourself. Or worse, you might make a mistake designing your next antenna.

We’ll explain. [Gregg Messenger (VE6WO)] asked a seemingly simple question about antenna theory: Does an impedance mismatch between the antenna and a coaxial feedline result in common-mode current on the coax shield? It’s an important practical matter, as any ham who has had the painful experience of “RF in the shack” can tell you. They also will likely tell you that common-mode current on the shield is caused by an unbalanced antenna system, not an impedance mismatch. But when [Gregg] asked Google Gemini and ChatGPT that question, the answer came back that impedance mismatch can cause current flow on the shield. So who’s right?

In the first video below, [Gregg] built a simulated ham shack using a 100-MHz signal generator and a length of coaxial feedline. Using a toroidal ferrite core with a couple of turns of magnet wire and a capacitor as a current probe for his oscilloscope, he was unable to find a trace of the signal on the shield even if the feedline was unterminated, which produces the impedance mismatch that the chatbots thought would spell doom. To bring the point home, [Gregg] created another test setup in the second video, this time using a pair of telescoping whip antennas to stand in for a dipole antenna. With the coax connected directly to the dipole, which creates an unbalanced system, he measured a current on the feedline, which got worse when he further unbalanced the system by removing one of the legs. Adding a balun between the feedline and the antenna, which shifts the phase on each leg of the antenna 180° apart, cured the problem.

We found these demonstrations quite useful. It’s always good to see someone taking a chatbot to task over myths and common misperceptions. We look into baluns now and again. Or even ununs.

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Random Wire Antenna Uses No Wire

November 5, 2024 by 40 Comments

Ideally, if you are going to transmit, you want a properly-tuned resonant antenna. But, sometimes, it isn’t practical. [Ham Radio Rookie] knew about random wire antennas but didn’t want a wire antenna. So, he took carbon fiber extension poles and Faraday tape and made a “random stick” antenna. You can check it out in the video below.

We aren’t sure what normal people are doing with 7-meter-long telescoping poles, but — as you might expect — the carbon fiber is not particularly conductive. That’s where the tape comes in. Each section gets some tape, and when you stretch it out, the tape lines up.

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Few Things Are Cheaper Than This Antenna

October 31, 2024 by 44 Comments

As far as hobbies go, ham radio tends to be on the more expensive side. A dual-band mobile radio can easily run $600, and a high-end HF base station with the capability of more than 100 watts will easily be in the thousands of dollars. But, like most things, there’s an aspect to the hobby that can be incredibly inexpensive and accessible to newcomers. Crystal radios, for example, can be built largely from stuff most of us would have in our parts drawers, CW QRP radios don’t need much more than that, and sometimes even the highest-performing antennas are little more than two lengths of wire.

For this specific antenna, [W3CT] is putting together an inverted-V which is a type of dipole antenna. Rather than each of the dipole’s legs being straight, the center is suspended at some point relatively high above ground with the two ends closer to the earth. Dipoles, including inverted-Vs, are resonant antennas, meaning that they don’t need any tuning between them and the radio so the only thing needed to match the antenna to the feed line is a coax-to-banana adapter. From there it’s as simple as attaching the two measured lengths of wire for the target band and hoisting the center of the antenna up somehow. In [W3CT]’s case he’s using a mast which would break the $8 budget, but a tree or building will do just as well.

The video on the construction of this antenna goes into great detail, so if you haven’t built a dipole yet or you’re just getting started on your ham radio journey, it’s a great place to get started. From there we’d recommend checking out an off-center-fed dipole which lets a dipole operate efficiently on multiple bands instead of just one, and for more general ham radio advice without breaking the bank we’d always recommend the $50 Ham series.

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Supercon 2023: Receiving Microwave Signals From Deep-Space Probes

October 10, 2024 by 5 Comments

Here’s the thing about radio signals. There is wild and interesting stuff just getting beamed around all over the place. Phrased another way, there are beautiful signals everywhere for those with ears to listen. We go about our lives oblivious to most of them, but some dedicate their time to teasing out and capturing these transmissions.

David Prutchi is one such person. He’s a ham radio enthusiast that dabbles in receiving microwave signals sent from probes in deep space. What’s even better is that he came down to Supercon 2023 to tell us all about how it’s done!

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Broadcast TV Simulator Keeps The Nostalgia Flowing

September 26, 2024 by 40 Comments

Watch out, Gen X-ers — there’s a nostalgia overload heading your way, courtesy of this over-the-air TV simulator. And it has us feeling a little Saturday morning cartoon-ish, or maybe even a bit Afterschool Special.

[Shane C Mason]’s “FieldStation42” build centers around a period-correct color TV, and rightly so — a modern TV would be jarring here, and replacing the CRT in this irreplaceable TV would be unthinkable. Programming comes via painstakingly collected sitcoms, dramas, news broadcasts, and specials, all digitized and stored on disk and organized by the original networks the programs came from. Python running on a Raspberry Pi does the heavy lifting here, developing a schedule of programs for the week that makes sense for the time of day — morning news and talk, afternoon soaps, the usual family hour and prime time offerings, and finally [Carson] rounding out the day, because that’s all we had for late night.

As for switching between stations, rather than risk damaging the old TV, [Shane] really upped his nostalgia game and found an old antenna rotator control box. These were used to steer the directional antenna toward different transmitters back in the day, especially in fringe areas like the one he grew up in. He added a set of contacts to the knob and a Pi Pico, which talks to the main Pi and controls which “channel” is being viewed. He also added an effect of fading and noise in the video and audio between channels, simulating the antenna moving. The video below shows it in action.

For those who missed the Golden Age of TV, relax; as [Shane] correctly surmises after going through this whole project, Golden Ages only exist in your mind. Things were certainly different with 70s mass media, a fact which this build captures neatly, but that doesn’t mean they were better. Other than Saturday mornings, of course — those were objectively better in every way.

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