QRP

29 Articles

You’ve Got The Portable Radio, Now What About The Antenna?

July 28, 2024 by 10 Comments

There’s an old saying in the amateur radio community that when it comes to antennas all you need is a piece of wet string. This may be a little fanciful, but it’s certainly true that an effective antenna can be made with surprisingly little in the way of conductor. It’s something [Evan Pratten VZ3ZZA] demonstrates amply with a description of the antenna he took camping in a Canadian provincial park.

Most of us would try some form of dipole on our adventures, but the antenna he’s using caught our eye as it’s described as an end-fed half-wave, but it has both a half-wave and quarter-wave element. Made from speaker cable or in this case thin mains cable for lamps, it’s obviously far from a perfect match and requires an ATU, but it generates an impressive array of FT4 contacts on a pretty meagre power level. We particularly like his in-plain-sight test run in the parking lot of a supermarket.

We frequently talk about the diversity of pursuits in amateur radio aside from that of the chequebook ham, and this project shows one of those. The world of QRP, operating at extreme low power, is not expensive to enter and can be extremely rewarding.

Tiny Transceiver Gets It Done With One Transistor

July 12, 2024 by 23 Comments

When we first spotted the article about a one-transistor amateur radio transceiver, we were sure it was a misprint. We’ve seen a lot of simple low-power receivers using a single transistor, and a fair number of one-transistor transmitters. But both in one package with only a single active component? Curiosity piqued.

It turns out that [Ciprian Popica (YO6DXE)]’s design is exactly what it says on the label, and it’s pretty cool to boot. The design is an improvement on a one-transistor transceiver called “El Pititico” and is very petite indeed. The BOM has only about fifteen parts including a 2N2222 used as a crystal-controlled oscillator for both the transmitter and the direct-conversion receiver, along with a handful of passives and a coupe of hand-wound toroidal inductors. There’s no on-board audio section, so you’ll have to provide an external amplifier to hear the signals; some might say this is cheating a bit from the “one transistor” thing, but we’ll allow it. Oh, and there’s a catch — you have to learn Morse code, since this is a CW-only transmitter.

As for construction, [Ciprian] provides a nice PCB  layout, but the video below seems to show a more traditional “ugly style” build, which we always appreciate. The board lives in a wooden box small enough to get lost in a pocket. The transceiver draws about 1.5 mA while receiving and puts out a fairly powerful 500 mW signal, which is fairly high in the QRP world. [Ciprian] reports having milked a full watt out of it with some modifications, but that kind of pushes the transistor into Magic Smoke territory. The signal is a bit chirpy, too, but not too bad.

We love minimalist builds like these; they always have us sizing up our junk bin and wishing we were better stocked on crystals and toroids. It might be good to actually buckle down and learn Morse too.

Continue reading “Tiny Transceiver Gets It Done With One Transistor” →

A Tiny Tuner For The Low Power Ham

May 18, 2024 by 10 Comments

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!

Emails Over Radio

April 9, 2024 by 38 Comments

The modern cellular network is a marvel of technological advancement that we often take for granted now. With 5G service it’s easy to do plenty of things on-the-go that would have been difficult or impossible even with a broadband connection to a home computer two decades ago. But it’s still reliant on being close to cell towers, which isn’t true for all locations. If you’re traveling off-grid and want to communicate with others, this guide to using Winlink can help you send emails using a ham radio.

While there are a number of ways to access the Winlink email service, this guide looks at a compact, low-power setup using a simple VHF/UHF handheld FM radio with a small sound card called a Digirig. The Digirig acts as a modem for the radio, allowing it to listen to digital signals and pass them to the computer to decode. It can also activate the transmitter on the radio and send the data from the computer out over the airwaves. When an email is posted to the Winlink outbox, the software will automatically send it out to any stations in the area set up as a gateway to the email service.

Like the cellular network, the does rely on having an infrastructure of receiving stations that can send the emails out to the Winlink service on the Internet; since VHF and UHF are much more limited in range than HF this specific setup could be a bit limiting unless there are other ham radio operators within a few miles. This guide also uses VARA, a proprietary protocol, whereas the HF bands have an open source protocol called ARDOP that can be used instead. This isn’t the only thing these Digirig modules can be used for in VHF/UHF, though. They can also be used for other digital modes like JS8Call, FT8, and APRS.

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Altoids Tin Spy Radio Goes Solid State

September 21, 2023 by 9 Comments

[Helge Fykse (LA6NCA)] has a type, as they say. At least as far as radios are concerned, he seems to prefer elegant designs that keep the BOM to the minimum needed to get the job done. And Altoids tins — he really seems to like putting radios in Altoids tins.

This QRP transceiver for the 60-meter amateur radio band is a perfect example of that ethos. For the unfamiliar, QRP is Morse code shorthand for decreased power, and is generally used when hams are purposely building and operating radios that radiate very little power, typically below a watt. For this transceiver, [Helge] chose to use modern components, a marked but interesting departure from his recent tube-powered spy radios. The design is centered on a custom oscillator board he designed using an Arduino Pro Mini and an Si5351 oscillator chip. Other components include an ADE-1ASK frequency mixer, an antenna tuner module that can be swapped out for operating on different bands, a receiver that’s little more than a couple of op-amps, and a Darlington pair for an RF power amplifier. Everything fits neatly on a piece of copper-clad board inside the tin box.

As is his tradition, [Helge] was on the air in the field with this radio almost before the solder had time to cool. His first contact was a 240-km shot to a friend, who reported a fine signal from this little gem. And that’s with just powering it off a 9-volt battery when it’s designed to the typical 12-volt supplies hams favor; he estimates this resulted in a signal of about 200 mW. Not too shabby.

Honestly, we’d love to learn more about that oscillator board [Helge] used, and maybe get a schematic for it. We found a little bit about it on his web page, but not the juicy details. If you’re out there, [Helge], please share the wealth.

Continue reading “Altoids Tin Spy Radio Goes Solid State” →

Off-Grid Radio Also Repairable Off-Grid

August 19, 2023 by 33 Comments

Low-power radios, often referred to in the amateur radio community as QRP radios, have experienced a resurgence in popularity lately. Blame it on certain parts of the hobby become more popular, like Parks on the Air (POTA) or Summits on the Air (SOTA). These are events where a radio operator operates off-grid at remote parks or mountaintops. These QRP rigs are a practical and portable way to make contacts. You would think that a five- or ten-watt rig running on batteries would be simple. Surprisingly, they can be enormously complex and expensive. That’s why [Dr. Daniel Marks] built the RFBitBanger, a QRP radio designed to not only be usable off-grid but to be built and maintained off-grid as well.

The radio accomplishes this goal by being built out of as many standard off-the-shelf components as possible. It eschews modern surface-mount components in favor of the much more accessible through-hole parts, including the ATMEGA328P at the center of the build. A PCB design is also available, but it can be built on perf board nearly as easily. The radio supports any mode a QRP operator might use, including CW, SSB, RTTY, and a new mode designed explicitly for this radio called SCAMP which is a low bandwidth, low SNR digital mode built into the Arduino-based firmware. It’s a single-band radio, but any band between 20 and 80 meters can be selected with pluggable filters.

As far as bomb-proof radios go, we can’t imagine a better way to live out an apocalypse than with a radio like this. As long as there’s a well-stocked parts drawer around, this radio could theoretically reach around the world without worrying about warranty claims, expensive parts, or even a company going out of business or not stocking parts for old radios anymore. There’s also more information about this build at the Open Research Institute for those interested. And, if you’re wondering how useful any radio could be using only five watts of transmitter power, take a look at this in-depth look at QRP radio operation.

Thanks to [Stephen Walters] for the tip.

The Peak Of Vacuum Tube Radio Design

May 12, 2023 by 19 Comments

One of the more popular trends in the ham radio community right now is operating away from the shack. Parks on the Air (POTA) is an excellent way to take a mobile radio off-grid and operate in the beauty of nature, but for those who want to take their rig to more extreme locations there’s another operating award program called Summits on the Air (SOTA) that requires the radio operator to set up a station on a mountaintop instead. This often requires lightweight, low-power radios to keep weight down for the hike, and [Dan] aka [AI6XG] has created a radio from scratch to do just that.

[Dan] is also a vacuum tube and CW (continuous wave/Morse code) operator on top of his interest in summiting various mountains, so this build incorporates all of his interests. Most vacuum tubes take a lot of energy to operate, but he dug up a circuit from 1967 that uses a single tube which can operate from a 12 volt battery instead of needing mains power, thanks to some help from a more modern switch-mode power supply (SMPS). The SMPS took a bit of research, though, in order to find one that wouldn’t interfere with the radio’s operation. That plus a few other modern tweaks like a QCX interface and a switch to toggle between receive to transmit easily allows this radio to be quite versatile when operating while maintaining its portability and durability when summiting.

For those looking to replicate a tube-based radio like this one, [Dan] has made all of the schematics available on his GitHub page. The only other limitation to keep in mind with a build like this is that it tends to only work on a very narrow range of frequencies without adding further complexity to the design, in this case within the CW portion of the 40-meter band. But that’s not really a bad thing as most radios with these design principles tend to work this way. For some other examples, take a look at these antique QRP radios for operating using an absolute minimum of power.