Bent Electric Field Explains Antenna Radiation

We all use antennas for radios, cell phones, and WiFi. Understanding how they work, though, can take a lifetime of study. If you are rusty on the basic physics of why an antenna radiates, have a look at the very nice animations from [Learn Engineering] below.

The video starts with a little history. Then it talks about charges and the field around them. If the charge moves at a constant speed, it also has a constant electric field around it. However, if the charge accelerates or decelerates, the field has to change. But the field doesn’t change everywhere simultaneously.

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NanoVNA Is A $50 Vector Network Analyzer

There was a time when oscilloscopes were big and expensive. Now you can get scopes of various sizes and capabilities on nearly any budget. Vector network analyzers — VNAs — haven’t had quite the same proliferation, but NanoVNA may change that. [IMSAI Guy] bought one for about $50 and made a series of videos about it. Spoiler alert: he likes it. You can see one of the several videos he’s posted, below.

NanoVNA is tiny but sweeps from 50 kHz to 900 MHz and has a touch screen. The device uses a rechargeable battery if you need to haul it up to an antenna tower, for example. Just as a quick test, you can see early in the video the analysis of a rubber duck antenna. The device shows return loss as a plot and you can use a cursor to precisely measure the values. It also shows a Smith chart of the reactance.

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L Band Satellite Antennas Revealed

[SignalsEverywhere] has a lot of satellite antennas and he’s willing to show them off — inside and out — in his latest video that you can see below. Using software-defined radio techniques, you can use these antennas to pull off weather satellite images and other space signals.

A lot of these antennas are actually made for some commercial purpose like keeping ships connected to Inmarsat. In fact, the shipborne antenna has a nice motorized system for pointing the antenna that [SignalsEverywhere] is hoping to modify for his own purposes.

With what appears to be standard NEMA 17 steppers onboard, it should be relatively easy to supplant the original controller with an Arduino and CNC shield. Though considering the resale value these particular units seem to have on eBay, we might be inclined to just roll our own positioner.

The QHF QFH antenna is another interesting teardown. The antenna makes a helix shape and looks like it would be interesting to build from scratch. There isn’t a lot of details about the antenna designs, but it is interesting to see the variety and range of antennas and how they appear internally.

L band is from 1 GHz to 2 GHz, so signals and antennas get very strange at these frequencies. The wavelength of a 2GHz signal is only 15cm, so small antennas can work quite well and are often as much mechanical designs as electrical. The L band contains everything from GPS to phone calls to ADS-B.

We’ve seen radiosonde antennas reborn before. Dish antenna repurposing is also popular.

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Antenna Tuning For GHz Frequencies

Antenna tuning at HF frequencies is something that radio amateurs learn as part of their licence exam, and then hone over their time operating. A few basic instruments and an LC network antenna tuner in a box are all that is required, and everything from a bit of wet string to ten thousand dollars worth of commercial antenna can be loaded up and used to work the world. When a move is made into the gigahertz range though it becomes a little more difficult. The same principles apply, but the variables of antenna design are much harder to get right and a par of wire snippers and an antenna tuner is no longer enough. With a plethora of GHz-range electronic devices surrounding us there has been more than one engineer sucked into a well of doom by imagining that their antenna design would be an easy task.

An article from Baseapp then makes for very interesting reading. Titled “Antenna tuning for beginners“, it approaches the subject from the perspective of miniature GHz antennas for IoT devices and the like. We’re taken through the basics and have a look at different types of antennas and connectors, before being introduced to a Vector Network Analyser, or VNA. Here is where some of the Black Art of high frequency RF design is laid bare, with everything explained through a series of use cases.

Though many of you will at some time or other work with these frequencies it’s very likely that few of you will do this kind of design exercise. It’s hard work, and there are so many ready-made RF modules upon which an engineer has already done the difficult part for you. But it does no harm to know something about it, so it’s very much worth taking a look at this piece.

It’s an area we’ve ventured into before, at a Superconference a few years ago [Michael Ossmann] gave us a fundamental introduction to RF design.

The Physics Behind Antennas

If you have done any sort of radio work you probably have a fair idea about what antennas do. It is pretty easy to have a cursory understanding of them, too. You probably know there’s something magic about antennas that are a quarter wave long or a half wave long and other multiples. But do you know why that matters? Do you understand the physics of why wire in a special configuration will cause signals to propagate through space? [Learn Engineering] does, and their new video is one of the best graphical explanations of what’s really going on in an antenna that we’ve seen. You can watch the video below.

If you tackle antennas using math, it is a long discussion. However, this video is about 8 minutes long and uses some great graphics to show how moving charges can produce a propagating electromagnetic field.

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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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The $50 Ham: Dummy Loads, Part 2

In the last installment of “The $50 Ham” I built a common tool used by amateur radio operators who are doing any kind of tuning or testing of transmitters: a dummy load. That build resulted in “L’il Dummy”, a small dummy load intended for testing typical VHF-UHF handy talkie (HT) transceivers, screwing directly into the antenna jack on the radio.

As mentioned in the comments by some readers, L’il Dummy has little real utility. There’s actually not much call for a dummy load that screws right into an HT, and it was pointed out that a proper dummy load is commercially available on the cheap. I think the latter observation is missing the point of homebrewing specifically and the Hackaday ethos in general, but I will concede the former point. That’s why at the same time I was building L’il Dummy, I was building the bigger, somewhat more capable version described here: Big Dummy.

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