PI4ZLB

When you buy a cheap ham radio handy-talkie, you usually get a little “rubber ducky” antenna with it. You can also buy many replacement ones that are at least longer. But how good are they? [Learnelectronics] wanted to know, too, so he broke out his NanoVNA and found out that they were all bad, although some were worse than others. You can see the results in the — sometimes fuzzy — video below.

Of course, bad is in the eye of the beholder and you probably suspected that most of them weren’t super great, but they do seem especially bad. So much so, that, at first, he suspected he was doing something wrong. The SWR was high all across the bands the antennas targeted.

It won’t come as a surprise to find that making an antenna work at 2 meters and 70 centimeters probably isn’t that easy. In addition, it is hard to imagine the little stubby antenna the size of your thumb could work well no matter what. Still, you’d think at least the longer antennas would be a little better.

Hams have had SWR meters for years, of course. But it sure is handy to be able to connect an antenna and see its performance over a wide band of frequencies. Some of the antennas weren’t bad on the UHF band. That makes sense because the antenna is physically larger but at VHF the size didn’t seem a big difference.

He even showed up a little real-world testing and, as you might predict, the test results did not lie. However, only the smallest antenna was totally unable to hit the local repeater.

Of course, you can always make your own antenna. It doesn’t have to take much.

A tuned circuit formed by a capacitor and an inductor is a familiar enough circuit, and it’s understood that it will resonate at a particular frequency. As that frequency increases, so the size of the capacitor and inductor decrease, and there comes a point at which they can become the characteristic capacitance and inductance of a transmission line. These tuned circuits can be placed in an enclosure, at which they can be designed for an extremely high Q factor, a measure of quality, and thus a very narrow resonant point. They are frequently used as filters for that reason, and [Fesz] is here with a video explaining some of their operation and configurations.

Some of the mathematics behind RF design can be enough to faze any engineer, but he manages to steer a path away from that rabbit hole and explain cavity filters in a way that’s very accessible. We learn how to look at tuned circuits as transmission lines, and the properties of the various different coupling methods. Above all it reveals that making tuned cavities is within reach.

They’re a little rare these days, but there was a time when almost every TV set contained a set of these cavities which were ready-made for experimentation.

Have you ever thought about getting into digital modes on the ham bands? As it turns out, you can get involved using the affordable and popular Quansheng UV-K6 — if you’re game to modify it, that is. It’s perfectly achievable using the custom Mobilinkd firmware, the brainchild of one [Rob Riggs].

In order to efficiently transmit digital modes, it’s necessary to make some hardware changes as well. Low frequencies must be allowed to pass in through the MIC input, and to pass out through the audio output. These are normally filtered out for efficient transmission of speech, but these filters mess up digital transmissions something fierce.  This is achieved by messing about with some capacitors and bodge wires. Then, one can flash the firmware using a programming cable.

With the mods achieved, the UV-K6 can be used for transmitting in various digital modes, like M17 4-FSK. The firmware has several benefits, not least of which is cutting turnaround time. This is the time the radio takes to switch between transmitting and receiving, and slashing it is a big boost for achieving efficient digital communication. While the stock firmware has an excruciating slow turnaround of 378 ms, the Mobilinkd firmware takes just 79 ms.

Further gains may be possible in future, too. Bypassing the audio amplifier could be particularly fruitful, as it’s largely in the way of the digital signal stream.

Quansheng’s radios are popular targets for modification, and are well documented at this point.

Everyone who deals with electronics knows that grounding is important. Your house has a copper rod in the ground. But [Kristen K6WX] has news: the idea of ground is kind of a myth. She explained at a talk at the recent ARRL National Convention, and if you didn’t make it, you can watch it in the video below.

The problem is analogous to finding something that is standing still. You really can only talk about something standing still relative to something else. Sure, you might be standing still outside a building, but seen from the moon, you and the building are spinning around at about one revolution per day. If you were sitting on the sun and not burning up, you’d see lots of motion of everything, and, of course, the sun itself is moving in the right frame of reference.

So what’s ground? Just a common reference between two things. [Kristen] gets into RF grounds, DC grounds, and phasors. If you’ve ever wanted to ground your antenna or deal with RF interference, you’ll find a lot of information in this 45-minute video.

The name ground is, perhaps, unfortunate. You do want earth grounding for lightning protection, but what most of us think of as ground is just a convention. Need a -9V battery? Just reverse your meter leads, and there you go.

Getting a good common reference can be maddening. We’ve looked at way too many ground loops before.

Stay in the amateur radio hobby long enough and you might end up with quite a collection of antennas. With privileges that almost extend from DC to daylight, one antenna will rarely do everything, and pretty soon your roof starts to get hard to see through the forest of antennas. It may be hell on curb appeal, but what’s a ham to do?

One answer could be making one antenna do the work of two, as [Guido] did with this diplexer for dual APRS setups. Automatic Packet Reporting System is a packet radio system used by hams to transmit telemetry and other low-bandwidth digital data. It’s most closely associated with the 2-meter ham band, but [Guido] has both 2-meter (144.8-MHz) and 70-cm LoRa (433.775-MHz) APRS IGates, or Internet gateway receivers. His goal was to use a single broadband discone antenna for both APRS receivers, and this would require sorting the proper signals from the antenna to the proper receiver with a diplexer.

Note that [Guido] refers to his design as a “duplexer,” which is a device to isolate and protect a receiver from a transmitter when they share the same antenna — very similar to a diplexer but different. His diplexer is basically a pair of filters in parallel — a high-pass filter tuned to just below the 70-cm band, and a low-pass filter tuned just above the top of the 2-m band. The filters were designed using a handy online tool and simulated in LTSpice, and then constructed in classic “ugly” style. The diplexer is all-passive and uses air-core inductors, all hand-wound and tweaked by adjusting the spacing of the turns.

[Guido]’s diplexer performs quite well — only a fraction of a dB of insertion loss, but 45 to 50 dB attenuation of unwanted frequencies — pretty impressive for a box full of caps and coils. We love these quick and dirty tactical builds, and it’s always a treat to see RF wizardry in action.

Something that all radio amateurs encounter sooner or later is the subject of impedance matching. If you’d like to make sure all that power is transferred from your transmitter into the antenna and not reflected back into your power amplifier, there’s a need for the impedance of the one to match that of the other. Most antennas aren’t quite the desired 50 ohms impedance, so part of the standard equipment becomes an antenna tuner — an impedance matching network. For high-power hams these are big boxes full of chunky variable capacitors and big air cored inductors, but that doesn’t exclude the low-power ham from the impedance matching party. [Barbaros Aşuroğlu WB2CBA] has designed the perfect device for them: the credit card ATU.

The circuit of an antenna tuner is simple enough, two capacitors and an inductor in a so-called Pi-network because of its superficial resemblance to the Greek letter Pi. The idea is to vary the capacitances and inductance to find the best match, and on this tiny model it’s done through a set of miniature rotary switches. There are a set of slide switches to vary the configuration or switch in a load, and there’s even a simple matching indicator circuit.

We like this project, in that it elegantly provides an extremely useful piece of equipment, all integrated into a tiny footprint. It’s certainly not the first ATU we’ve brought you.

Thanks [ftg] for the tip!

How may radios do you own? Forget the AM/FM, GMRS/FRS radios you listen to or communicate with. We’re talking about the multiple radios and antennae in your phone, your TV, your car, your garage door opener, every computing device you own- you get the idea. It’s doubtful that you can accurately count them even in your own home. But what principles of the electromagnetic spectrum allow radio to work, and how do antenna design, modulation, and mixing affect it? [Michał Zalewski] aka [lcamtuf] aims to inform you with his excellent article Radios, how do they work?

For those of you with a penchant for difficult maths, there’s some good old formulae published in the article that’ll help you understand the physics of radio. For the rest of us, there are a plethora of fantastic illustrations showing some of the less obvious principals, such as why a longer diploe is more directional than a shorter dipole.

The article opens with a thought experiment, explaining how two dipole antennae are like capacitors, but then also explains how they are different, and why a 1/4 wave dipole saves the day. Of course it doesn’t stop there. [lcamtuf]’s animations show the action of a sine wave on a 1/4 wave dipole, bringing a nearly imaginary concept right into the real world, helping us visualize one of the most basic concepts of radio.

Now that you’re got a basic understanding of how radios work, why not Listen to Jupiter with your own homebrew receiver?