RTL-SDR: Seven Years Later

Before swearing my fealty to the Jolly Wrencher, I wrote for several other sites, creating more or less the same sort of content I do now. In fact, the topical overlap was enough that occasionally those articles would get picked up here on Hackaday. One of those articles, which graced the pages of this site a little more than seven years ago, was Getting Started with RTL-SDR. The original linked article has long since disappeared, and the site it was hosted on is now apparently dedicated to Nintendo games, but you can probably get the gist of what it was about from the title alone.

An “Old School” RTL-SDR Receiver

When I wrote that article in 2012, the RTL-SDR project and its community were still in their infancy. It took some real digging to find out which TV tuners based on the Realtek RTL2832U were supported, what adapters you needed to connect more capable antennas, and how to compile all the software necessary to get them listening outside of their advertised frequency range. It wasn’t exactly the most user-friendly experience, and when it was all said and done, you were left largely to your own devices. If you didn’t know how to create your own receivers in GNU Radio, there wasn’t a whole lot you could do other than eavesdrop on hams or tune into local FM broadcasts.

Nearly a decade later, things have changed dramatically. The RTL-SDR hardware and software has itself improved enormously, but perhaps more importantly, the success of the project has kicked off something of a revolution in the software defined radio (SDR) world. Prior to 2012, SDRs were certainly not unobtainable, but they were considerably more expensive. Back then, the most comparable device on the market would have been the FUNcube dongle, a nearly $200 USD receiver that was actually designed for receiving data from CubeSats. Anything cheaper than that was likely to be a kit, and often operated within a narrower range of frequencies.

Today, we would argue that an RTL-SDR receiver is a must-have tool. For the cost of a cheap set of screwdrivers, you can gain access to a world that not so long ago would have been all but hidden to the amateur hacker. Let’s take a closer look at a few obvious ways that everyone’s favorite low-cost SDR has helped free the RF hacking genie from its bottle in the last few years.

Hardware Evolution

Even though the project is called RTL-SDR, the Realtek RTL2832U chip is in reality just half of the equation; it’s a USB demodulator chip that needs to be paired with a tuner to function. In the early days, there were a number of different tuners in use, and figuring out which one you were getting was a pretty big deal. The Elonics E4000 was the most desirable tuner as it had the widest frequency range, but it could be difficult to know ahead of time what you were getting.

The packaging and documentation were all but useless; either the manufacturer didn’t bother to include the information, or if they did, it would often become outdated as new revisions of the product were produced. The only way to be sure about what you were getting was to see if somebody had already purchased that particular model and reported on their findings. Luckily, the tuners were cheap enough that you could buy a couple and experiment. In those days, it wasn’t uncommon to find RTL-SDR compatible devices for less than $10 from import sites.

Opening up a contemporary RTL2832U+E4000 receiver, we can see they were relatively simple affairs. The flimsy plastic case doesn’t do much to prevent interference, and the Belling-Lee connector connector is intended for use with a traditional TV antenna. Note this particular model features an IR receiver so the user could change TV channels with the included remote; a reminder of what this device was actually built for.

These days, you don’t need to wade through pages of nearly identical looking USB TV tuners to find compatible hardware. There are now several RTL2832U-based receivers which are specifically designed for RTL-SDR use, generally selling for around $30. These devices not only address the shortcomings of the original hardware offerings, but in many cases add in new capabilities that simply wouldn’t have made sense to include back when they were just for watching TV on your computer.

Here we have the “RTL-SDR Blog v3” receiver, which is one of the most popular “next generation” RTL-SDR receivers. The plastic case has been replaced with an aluminum one that not only reduces interference, but helps the board dissipate heat while in operation. The crystal has been upgraded to a temperature compensated oscillator (TCXO) which helps reduce temperature drift. The R820T2 tuner is paired with a standard SMA antenna connector, and both it and the RTL2832U have some unused pins broken out if you’re looking to get into developing modifications or expansions to the core hardware.

Software Library

The improvements to the base RTL-SDR hardware are welcome, and it’s nice to not have to worry about whether or not the receiver you’ve purchased is actually going to work with the drivers, but realistically those changes mainly benefit the more hardcore users who are pushing the edge of the envelope. If you’re just looking to sniff some 433 MHz thermometers, you don’t exactly need a TCXO. For most users, the biggest improvements have come in the software side of things.

For one, the RTL-SDR package is almost certainly going to be in the repository of your favorite GNU/Linux distribution. Unless you need some bleeding edge feature, you won’t have to compile the driver and userland tools from source anymore. The same will generally be true for the SDR graphical frontend, namely gqrx by Alexandru Csete. Those two packages are enough to get you on the air and browsing for interesting signals, but that’s just the beginning. The rise of cheap SDRs has inspired a number of fantastic new software packages that are light-years ahead of what was available previously.

Certainly one of the best examples is Universal Radio Hacker, an all-in-one tool that lets you search for, capture, and ultimately decode wireless signals. Whether it’s a known protocol for which it already has a built-in decoder, or something entirely new that you need to reverse engineer, Universal Radio Hacker is a powerful tool for literally pulling binary data out of thin air. Those looking to reverse unknown wireless protocols should also take a look at inspectrum, another tool developed in the last few years that can be used to analyze captured waveforms.

Decoding a captured ASK OOK signal in Universal Radio Hacker

If you’re more interested in the practical application of these radios, there have also been a number of very impressive “turn-key” applications developed that leverage the high availability of low-cost SDRs. One such project is dump1090, a ADS-B decoder that was specifically developed for use with the RTL-SDR. With a distributed network of receivers, the software has allowed the community to democratize flight tracking through the creation of open data aircraft databases.

The Gift of Inspiration

In the years since its inception, the RTL-SDR project has become the de facto “first step” for anyone looking to experiment with radio. It’s cheap, it’s easy, and since the hardware is incapable of transmission, you don’t have to worry about accidentally running afoul of the FCC or your local equivalent. Honestly, it’s difficult to think of a valid reason not to add one of these little USB receivers to your bag of tricks; even if you only use it once, it will more than pay for itself.

Ultimately, this is the greatest achievement of the RTL-SDR project. It drove the entry barrier for radio experimentation and hacking so low that it’s spawned a whole new era. From the unique vantage point offered by Hackaday, we can see the sharp uptick of RF projects that correspond to the introduction of an easy to use and extremely affordable software defined radio. People who might never have owned a “real” radio beyond the one in their car can now peel back the layers of obscurity that in the past kept the vast majority of us off the airwaves. This is a very exciting time for wireless hacking, and things are only going to get more interesting from here on out. Long live RTL-SDR!

Repurposed Plastic Protects PCBs

An errant wire snipping across the wrong electrical pins spells the release of your magic smoke. Even if you are lucky, stray parts are the root of boundless malfunctions from disruptive to deadly. [TheRainHarvester] shares his trick for covering an Arduino Nano with some scrap plastic most of us have sitting in the recycling bin. The video is also after the break. He calls this potting, but we would argue it is a custom-made cover.

The hack is to cut a bit of plastic from food container lids, often HDPE or plastic #2. Trim a piece of it a tad larger than your unprotected board, and find a way to hold it in place so you can blast it with a heat gun. When we try this at one of our Hackaday remote labs and apply a dab of hot glue between the board and some green plastic it works well. The video suggests a metal jig which would be logical when making more than one. YouTube commenter and tip submitter [Keith o] suggests a vacuum former for a tighter fit, and we wouldn’t mind seeing custom window cutouts for access to critical board segments such as DIP switches or trimmers.

We understand why shorted wires are a problem, especially when you daisy-chain three power supplies as happened in one of [TheRainHarvester]’s previous videos.

 

X-Rays Are the Next Frontier in Space Communications

Hundreds of years from now, the story of humanity’s inevitable spread across the solar system will be a collection of engineering problems solved, some probably in heroic fashion. We’ve already tackled a lot of these problems in our first furtive steps into the wider galaxy. Our engineering solutions have taken humans to the Moon and back, but that’s as far as we’ve been able to send our fragile and precious selves.

While we figure out how to solve the problems keeping us trapped in the Earth-Moon system, we’ve sent fleets of robotic emissaries to do our exploration by proxy, to make the observations we need to frame the next set of engineering problems to be solved. But as we reach further out into the solar system and beyond, our exploration capabilities are increasingly suffering from communications bottlenecks that restrict how much data we can ship back to Earth.

We need to find a way to send vast amounts of data back as quickly as possible using as few resources as possible on both ends of the communications link. Doing so may mean turning away from traditional radio communications and going way, way up the dial and developing practical means for communicating with X-rays.

The Tyranny of Physics

The essential problems with deep space communications come from two sources – the inverse-square law and information theory. The inverse-square law states that the amount of energy at the receiving end of a radio communications link is inversely proportional to the square of the distance to the transmitter. Basically, radio waves spread out from the source and at very great distances tend to diminish into the background noise. That’s why deep-space communications networks tend to have large antennas on both ends of the link, to gather and focus as much of the weak signal as possible, as well as to be able to transmit a powerful and narrowly focused beam.

Information theory tells us that more data can be packed into higher frequency signals than lower frequencies. Early satellites didn’t need much bandwidth to do their jobs, so VHF and UHF radios were generally sufficient. But as spacecraft became more sophisticated and the amount of data they needed to send back increased, their communications links began shifting gradually up the electromagnetic spectrum into the microwave region. The Voyager probes, currently in interstellar space, have an uplink using 2.1 GHz for the relatively low-bandwidth tasks of vehicle control, with a downlink at 8.1 GHz, reflecting the increased bandwidth needed to send scientific data back to Earth.

For as stunning an engineering achievement as Voyager has been, and notwithstanding the fact that it’s still working more than 40 years after launch, its radio gear only barely supports its interstellar mission. To be fair, Voyager was never meant to last this long, and every bit of data that makes it back to Earth is just icing on the cake. But for future missions specifically designed for interstellar space, sending back enough data to make such missions feasible will require more bandwidth.

Small, Bright, and Fast

The Modulated X-Ray Source experiment. The miniature source is center bottom. Source: NASA/W. Hrybyk

In late April, NASA is sending a pallet of gear up to the ISS, and one of the experiments stashed in the cargo is meant to explore the potential for X-ray communications, or XCOM, for deep space. The Modulated X-Ray Source (MXS) is a compact X-ray transmitter that will be mounted outside the space station. The receiver for this experiment is already installed; the Neutron Star Interior Composition Explorer (NICER) has been gathering X-ray spectra from neutron stars since 2017, while also gathering data about the potential for using X-ray pulsars as navigational beacons in a sort of “Galactic Positioning System”.

MXS is an interesting instrument. When one thinks of making X-rays, the natural tendency is to assume a traditional hot-cathode vacuum tube, where electrons are boiled off a filament and accelerated by an electric field in the range of 100 kilovolts to slam into a tungsten anode, would be used. But vacuum tubes like those found in a hospital X-ray suite aren’t the best space travelers, and even when ruggedized they’re too bulky and heavy to send upstairs.

So NASA researchers developed a more spaceflight-friendly X-ray generator. Rather than heating a filament to generate electrons, the X-ray source in MXS uses creates photoelectrons by bombarding a magnesium photocathode with UV light from LEDs. The few photoelectrons produced then enter an electron amplifier, an off-the-shelf component found in mass spectrometers that uses specially shaped chambers coated with a thin layer of semiconducting material. Each incident electron liberates a few secondary photoelectrons, which bounce off the other wall of the multiplier to create more electrons, greatly amplifying the signal. The huge stream of electrons is then accelerated by a 10 kV field to collide with the target anode and produce X-rays.

Comparison of hot-cathode X-ray tube to MXS. Source: NASA

While the MXS source sounds similar to a hot-cathode tube, there are important differences. First, the source can be made cheaply from off-the-shelf components and a 3D-printed metal enclosure. The whole assembly weighs only about 160 grams, fits in the palm of a hand, and has no unusual power or temperature control requirements. The big difference, though, is with how fast the X-rays can be turned on and off. A glowing filament can only heat up and cool down so quickly, meaning that effective modulation of X-ray from hot-cathode sources is difficult. In the MXS, X-rays are produced only when the UV LEDs are on, and those can be switching very quickly, in the sub-nanosecond range. The ability to modulate an X-ray beam lead to data rates in the gigabits per second range, greatly enhancing our ability to move data around in space.

What’s more, X-rays can be more tightly collimated than radio waves or even light, which is also being experimented with for space communications. The tighter X-ray beam spreads out less, making transmission more power efficient and reception easier by virtue of the strong signal from relatively bright transmitters.

Although the distance between the MXS and NICER in these XCOM experiments is only about 50 meters, they stand to position us for much better bandwidth for deep space communications. The MXS source itself has a lot of potential applications beyond XCOM too, from cheap, lightweight, low-power medical imaging on Earth and in space, navigational beacons for spacecraft, and even advanced chemical analysis by X-ray spectroscopy

Full Earth Disc Images From GOES-17 Harvested By SDR

We’ve seen lots of hacks about capturing weather images from the satellites whizzing over our heads, but this nicely written how-to from [Eric Sorensen] takes a different approach. Rather than capturing images from polar satellites that pass overhead a few times a day, this article looks at capturing images from GOES-17, a geostationary satellite that looks down on the Pacific Ocean. The fact that it is a geostationary satellite means that it captures the same view all the time, so you can capture awesome time-lapse videos of the weather. 

The fact that GOES-17 is a geostationary satellite means that it is a bit more involved. While polar satellites that orbit at an altitude of 800km or so can be received with a random piece of wire, the 35,800 km altitude of geostationary satellites means that you need a better antenna. That doesn’t have to be that expensive, though: [Eric] used a $100 parabolic antenna and a $100 Airspy Mini SDR receiver connected to an Ubuntu laptop running some open source software to receive and decode the 1.7GHz signal of the satellite.

The other trick is to figure out where to point the dish. Because it is a geostationary satellite, this part has to be done carefully, as the parabolic antenna has only a small receiving angle. [Eric] designed a 3D-printed mount that fits onto a tripod for his antenna.

Capturing satellite weather images is a fascinating thing to do, and this adds another level of interest, as the images show the full disc of the earth. Capture a series over time, and you can see storms spin around and across the ocean, and see just how complicated they are.

If you are looking for a simpler way to get started in receiving weather satellite images, check out this guide to converting an old TV antenna and USB receiver to capture images from polar satellites.

The $50 Ham: Dummy Loads

This is an exciting day for me — we finally get to build some ham radio gear! To me, building gear is the big attraction of amateur radio as a hobby. Sure, it’s cool to buy a radio, even a cheap one, and be able to hit a repeater that you think is unreachable. Or on the other end of the money spectrum, using a Yaesu or Kenwood HF rig with a linear amp and big beam antenna to work someone in Antartica must be pretty cool, too. But neither of those feats require much in the way of electronics knowledge or skill, and at the end of the day, that’s why I got into amateur radio in the first place — to learn more about electronics.

To get my homebrewer’s feet wet, I chose perhaps the simplest of ham radio projects: dummy loads. Every ham eventually needs a dummy load, which is basically a circuit that looks like an antenna to a transmitter but dissipates the energy as heat instead of radiating it an appreciable distance. They allow operators to test gear and make adjustments while staying legal on emission. Al Williams covered the basics of dummy loads a few years back in case you need a little more background.

We’ll be building two dummy loads: a lower-power one specifically for my handy talkies (HTs) will be the subject of this article, while a bigger, oil-filled “cantenna” load for use with higher power transmitters will follow. Neither of my designs is original, of course; borrowing circuits from other hams is expected, after all. But I did put my own twist on each, and you should do the same thing. These builds are covered in depth on my Hackaday.io page, but join me below for the gist on a good one: the L’il Dummy.

L’il Dummy

As Al points out in the article linked above, a dummy load is just a resistive element that matches the characteristic impedance of the transmitter’s antenna connection. In almost every case, that’s going to be 50 ohms. The reason that the load needs to be as resistive as possible is that it needs to continue looking like a flat 50-ohm load no matter what frequency is applied to it. Any inductive or capacitive elements in the load will make it more reactive, changing the impedance as the input frequency changes. This could lead to RF power getting reflected back into the final amplifier transistors in the transmitter, possibly damaging them or destroying them altogether. Not what you’re looking for.

That means our resistive elements need to be as non-inductive as possible. But, they also need to be able to dissipate a lot of power. The HT dummy load, which I’ve dubbed L’il Dummy, needs to handle the 5 to perhaps 8 watts an HT can output. Trouble is, power resistors in that range are often wirewound, and a coil of wire will have too much inductance. We’ll need to be clever in sourcing components.

Looking down into L’il Dummy just before applying the torch. The RF Biscuit board is a handy little thing.

The circuit for L’il Dummy is hardly worth a schematic – it’s just an SMA jack with a 50-ohm resistor across the outer ground and the inner conductor. I chose to build the circuit on an RF Biscuit board. This is an open-source design that enables all kinds of handy little RF circuits — attenuators, filters, and as in this case, dummy loads. The resistive element I chose was a thick-film SMT device capable of dissipating 35 watts – way more than enough for this job. That and an edge-mount SMA jack should have been all I needed to make a working dummy load.

To my surprise, once I soldered the resistor to the RF Biscuit board, the dummy load was almost as good an antenna as the stock rubber ducky on my Baofeng HT. I was able to hit a local repeater through the dummy load without any issues. Clearly not a good design. To correct it, I put the whole thing into an enclosure made from 1″ copper pipe. Not cheap stuff, but not too bad, and I like the look of polished copper. Soldering the whole case together was a challenge that my big Weller soldering gun wasn’t up to, and trying to get everything heated up enough with a propane torch without overdoing the heat was a fun time.

Testing on a Budget

Now for the $50 question: does it work? I tested the resistance with a DMM and it comes out to just about 49 ohms, which is close enough in my book. But that’s DC resistance; what about impedance? I don’t have an antenna analyzer, so I trolled around and found a simple method for measuring impedance with only a function generator and an oscilloscope. My scope has a 20-MHz function generator built in, so I whipped up a quick test jig from a BNC jack and an SMA jack, connected in series through a leftover 1000-ohm resistor.

L’il Dummy test setup. Measure the p-p voltage on each side of the series resistance connecting the function generator to the dummy, and do a little math.

Applying a sine wave into the dummy load, measuring peak-to-peak voltages on each side of the resistance, and doing a little math is all that’s needed to characterize the impedance from 2.5 MHz to 20 MHz. The math is simple:

Z_x = \frac{V_2}{V_1 - V_2}R_{ref}

with V1 being the voltage across the input, V2 being the voltage across the output, and Rref being the actual value of the series resistance, which I measured at 998 Ohms.

And the results are pretty close to 50 Ohms, and flat across the tested band

f (MHz) V1 (V p-p) V2 (V p-p) Z (ohms)
20.0 1.49 0.062 43.3
15.0 1.89 0.082 45.3
10.0 2.57 0.113 45.9
5.0 3.90 0.173 46.3
2.5 4.70 0.217 48.3

I wish I could measure it at VHF and UHF frequencies, but that will have to wait until I get a function generator that goes up to 400 MHz or so. I doubt very much that a $50 budget would cover that, though.

Next Time

I had intended to cover both L’il Dummy and its bigger, somewhat smarter brother in one article, but I still have some testing to do on Big Dummy. I’ll cover that next time, and after that we’ll move onto measuring the output of a cheap Chinese HT and perhaps building a filter to clean it up.

The $50 Ham: Checking Out the Local Repeater Scene

So far in this series, we’ve covered the absolute basics of getting on the air as a radio amateur – getting licensed, and getting a transceiver. Both have been very low-cost exercises, at least in terms of wallet impact. Passing the test is only a matter of spending the time to study and perhaps shelling out a nominal fee, and a handy-talkie transceiver for the 2-meter and 70-centimeter ham bands can be had for well under $50. If you’re playing along at home, you haven’t really invested much yet.

The total won’t go up much this week, if at all. This time we’re going to talk about what to actually do with your new privileges. The first step for most Technician-class amateur radio operators is checking out the local repeaters, most of which are set up exactly for the bands that Techs have access to. We’ll cover what exactly repeaters are, what they’re used for, and how to go about keying up for the first time to talk to your fellow hams.

Could You Repeat That?

Basic repeater schematic. Source: Ham Radio School

Time to face some cold, hard facts about amateur radio: that spiffy new Baofeng radio I recommended last time as a great starter radio is actually pretty lame. That fact has little to do with the mere $25 you spent on it, or $40 if you opted to upgrade the antenna. It’s a simple consequence of physics: a radio that transmits at 5 watts will only have so much range on the VHF band, and even less on UHF. Even if you buy a more powerful HT, or invest in a mobile or base-station rig running 50 or 100 watts, the plain fact is that direct radio-to-radio contacts on the same frequency, or simplex contacts, are difficult on VHF and UHF because those bands are really best for line of sight (LOS) use.

That’s not to say that hams don’t use their VHF and UHF rigs for simplex communications, of course. Many hams like to see just how far they can push their signals on these bands, building big Yagi antennas and finding mountain peaks to operate from. But for general use around town, most hams rely on repeaters to extend the area they can communicate over. Repeaters are simply transceivers set up to receive signals on one frequency and transmit them on another at the same time, with the help of a device called a duplexer. This simultaneous reception and transmission gives rise to the term duplex communications, the general term for operating on a repeater.

Repeater usually transmit at a much higher power than an HT or even a mobile rig can manage, and they usually have the advantage of being located on a mountaintop or some other elevated place to gain the furthest possible radio horizon as possible. This arrangement vastly increases the area that you can cover with your tiny HT. Depending on how the repeater is sited and what sort of antenna it has, you may be able to cover hundreds of square miles, as opposed to perhaps a few miles radius under ideal conditions, or a few blocks in the typical urban or suburban setting with lots of clutter from buildings and trees. What’s more, some repeaters are linked to other repeaters either through backhaul connections, often via the Internet but also sometimes through powerful LOS microwave links. In these systems it’s possible to use a puny HT to talk to another ham over hundreds or even thousands of miles. It’s actually pretty cool.

Welcome to the Machine

So where are these repeaters, and how do you start working them? The first question is easy to answer: they’re everywhere. Look at any tall building, mountaintop antenna farm, or municipal water tank, and chances are pretty good there’s a ham repeater there. But being able to work them means you need to know exactly where they are, to be sure you’re in range of the repeater, or “the machine” as hams often refer to it, as well as the frequencies it operates on.

Luckily, there are online guides to help with that chore. RepeaterBook.com is usually the first place hams go to find machines in the area. There you can search by state, county, or city, or even via a map, and find what repeaters are available. They’ve even got a handy road search, so you can get all the repeaters listed as within range of a particular highway; that’s really handy for road-trip planning. Here’s what comes up for VHF and UHF repeaters when I search within 25 miles of my location, or QTH:

The first thing you’ll notice is that several machines at different sites have the same callsign. For example, K7ID runs a UHF repeater on Canfield Mountain and a VHF machine on Mica Peak. Both are LOS to me, and I can easily hit them with an HT. The frequency listed in the first column is the transmit frequency of the repeater. Your HT will need to be set to this frequency to hear what’s being said. Your radio will also need to be programmed for the correct tone, listed in the third column. That tone is an audio frequency signal known by a number of different trade names, but generically as continuous tone-coded squelch system (CTCSS). Your radio is capable of adding this sub-audible tone to your transmission; the repeater will only “open up” to transmissions that are correctly coded. Some repeaters have no tone coding, others have different tones for receive and transmit. When doubt, try to find out who runs the machine – most, but not all, are run by a ham radio club – and see if you can look up instructions on the web.

The offset shown in the second column is perhaps the most important bit of information. Recall that repeaters transmit and receive on different frequencies, and that they’re listed by their transmit frequency. The offset tells you what the repeater’s input frequency is, which is the frequency your radio will need to be set to transmit on. For example, the machine I most often used is the K7ID machine on Mica Peak. It’s at 146.980 and shows an offset of -0.6 MHz. That means that my radio has to be set to 146.380 MHz transmission frequency. VHF repeaters are usually 0.6 MHz, but could be plus or minus depending on which part of the VHF band they’re in. UHF repeaters usually have +5 MHz offsets.

Note: I’m not going to cover programming your radio, because there are plenty of guides online that do a better job than I can. DuckDuckGo is your friend.

Casting the Net

Once you’ve found your local repeaters and programmed your radio, it’s time to get on the air. My advice is to spend the first few days just listening to one or more repeaters. Activity levels vary – some machines are hopping all day, and some are barely used except during the typical commuting hours. When you hear a conversation, try to get a feeling for the culture of the repeater. Every group of hams has a culture, and as we discussed in the first installment of the series, it’s not always a healthy culture. My local repeater belongs to the Kootenai Amateur Radio Society, as friendly and as inviting a group of people as I’ve ever heard on the air. After listening to them chat for a few weeks, I was more than ready to reach out to them.

But first, a word about kerchunking. If you want to know if you’re in range of a repeater, you can test it out. Most repeaters have a “squelch tail” that keeps the repeater on the air for several seconds before going back to sleep, and this can be used to check if you’re in range. Some repeaters even identify themselves, either with a synthesized voice or Morse code when they “wake up”.  So you might want to ping the repeater.

Kerchunking, or transmitting into a repeater without identifying yourself, is one of those bad habits that everyone seems to have. But FCC part 97 rules, which cover the amateur radio service, require operators to transmit their call sign when they start a transmission. So don’t kerchunk; a simple identification like “This is KC1DJT testing and clear” will suffice. Nobody is likely to take that as an invitation to chat, but they might give you a reception report.

Once you’re feeling confident enough, try making a contact. I highly recommend checking out the local traffic networks. Hams pride themselves on having the skills and equipment to communicate in an emergency, but that means little without practice to keep everything sharp. Nets allow hams to practice message passing skills and to test their gear on a regular basis. My local group has a network check-in every night that follows a standard script and usually attracts about 30 check-ins. Here’s a sample from a recent check-in:

I’ve become a regular on this net and a few others, mainly because I want to practice, but also to get over my mic shyness. There’s another reason too – I want people to recognize my voice and callsign. If there ever is an emergency in my area, I feel like it’ll be easier to pitch in or to get help if I need it if people hear a familiar voice.

Next Time

Over the next few installments, we’re finally going to get to what I think ham radio is all about at its core: homebrewing. We’ll be building a few simple projects to make that cheap HT a little better, and also build a few tools to help run the shack a little more efficiently.

A New Digital Mode For Radio Amateurs

There used to be a time when amateur radio was a fairly static pursuit. There was a lot of fascination to be had with building radios, but what you did with them remained constant year on year. Morse code was sent by hand with a key, voice was on FM or SSB with a few old-timers using AM, and you’d hear the warbling tones of RTTY traffic generated by mechanical teletypes.

By contrast the radio amateur of today lives in a fast-paced world of ever-evolving digital modes, in which much of the excitement comes in pushing the boundaries of what is possible when a radio is connected to a computer. A new contender in one part of the hobby has come our way from [Guillaume, F4HDK], in the form of his NPR, or New Packet Radio mode.

NPR is intended to bring high bandwidth IP networking to radio amateurs in the 70 cm band, and it does this rather cleverly with a modem that contains a single-chip FSK transceiver intended for use in licence-free ISM band applications. There is an Ethernet module and an Mbed microcontroller board on a custom PCB, which when assembled produces a few hundred milliwatts of RF that can be fed to an off-the-shelf DMR power amplifier.

Each network is configured around a master node intended to use an omnidirectional antenna, to which individual nodes connect. Time-division multiplexing is enforced by the master so there should be no collisions, and this coupled with the relatively wide radio bandwidth of the ISM transceiver gives the system a high usable data bandwidth.

Whether or not the mode is taken up and becomes a success depends upon the will of individual radio amateurs. But it does hold the interesting feature of relying upon relatively inexpensive parts, so the barrier to entry is lower than it might be otherwise. If you are wondering where you might have seen [F4HDK] before, we’ve previously brought you his FPGA computer.

Bidirectional IP with New Packet Radio

There are a few options if you want to network computers on amateur radio. There are WiFi hacks of sort, and of course there’s always packet radio. New Packet Radio, a project from [f4hdk] that’s now on hackaday.io, is unlike anything we’ve seen before. It’s a modem that’s ready to go, uses standard 433 ISM band chips, should only cost $80 to build, and it supports bidirectional IP traffic.

The introductory documentation for this project (PDF) lays out the use case, protocol, and hardware for NPR. It’s based on chips designed for the 433MHz ISM band, specifically the SI4463 ISM band radio from Silicon Labs. Off the shelf amplifiers are used, and the rest of the modem consists of an Mbed Nucleo and a Wiznet W5500 Ethernet module. There is one single modem type for masters and clients. The network is designed so that a master serves as a bridge between Hamnet, a high-speed mesh network that can connect to the wider Internet. This master connects to up to seven clients simultaneously. Alternatively, there is a point-to-point configuration that allows two clients to connect to each other at about 200 kbps.

Being a 434 MHz device, this just isn’t going to fly in the US, but the relevant chip will work with the 915 MHz ISM band. This is a great solution to IP over radio, and like a number of popular amateur radio projects, it started with the hardware hackers first.

Es’hail-2: Hams Get Their First Geosynchronous Repeater

In the radio business, getting the high ground is key to covering as much territory from as few installations as possible. Anything that has a high profile, from a big municipal water tank to a roadside billboard to a remote hilltop, will likely be bristling with antennas, and different services compete for the best spots to locate their antennas. Amateur radio clubs will be there too, looking for space to locate their repeaters, which allow hams to use low-power mobile and handheld radios to make contact over a vastly greater range than they could otherwise.

Now some hams have claimed the highest of high ground for their repeater: space. For the first time, an amateur radio repeater has gone to space aboard a geosynchronous satellite, giving hams the ability to link up over a third of the globe. It’s a huge development, and while it takes some effort to use this new space-based radio, it’s a game changer in the amateur radio community.

Friends in High Places

The new satellite, Es’hail-2, was built for Es’hailSat, a Qatari telecommunications concern. As satellites go, it’s a pretty standard machine, built primarily to provide direct digital TV service to the Middle East and Africa. But interestingly, it was designed from the start to carry an amateur radio payload. The request for proposals (RFP) that Es’hailSat sent to potential vendors in early 2014 specifically called for the inclusion of an amateur repeater, to be developed jointly by AMSAT, the Radio Amateur Satellite Corporation.

The other kind of networking. His Excellency Al-Attiyah (A71AU). Source: Al-Attiyah International Foundation for Energy and Sustainable Development

The repeater aboard Es’hail-2 was developed as a joint effort between the Qatar Amateur Radio Society (QARS), Es’HailSat, and AMSAT-DL, the AMSAT group in Germany. The willingness of Es’HailSat to include an amateur radio payload on a commercial bird might be partially explained by the fact that the QARS chairman is His Excellency Abdullah bin Hamad Al Attiyah (A71AU), former Deputy Prime Minister of Qatar.

The repeater was engineered with two main services in mind. The first is a narrowband transponder intended for phone (voice) contacts, continuous wave (CW) for Morse contacts, and some of the narrow bandwidth digital modes, like PSK-31. The other transponder is for wideband use, intended to test Digital Amateur Television (DATV). The wideband transponder can carry two simultaneous HD signals and a beacon broadcasting video content from QARS. Both transponders uplink on the portion of the 2.4-GHz reserved for hams, while downlinking on the 10.4-GHz band.

Es’hail-2 was launched aboard a SpaceX Falcon 9 from Cape Canaveral on November 15, 2018. The satellite was boosted to a geosynchronous orbit in the crowded slot located at 26.5° East longitude, parking it directly above the Democratic Republic of Congo. After tests were completed, a ceremony inaugurating the satellite as “Qatar OSCAR-100”, or QO-100, was held on February 14, 2019, making it the 100th OSCAR satellite launched by amateurs.

Listening In

Sadly for hams in the Americas and most of eastern Asia, QO-100 is out of range. But for hams anywhere from coastal Brazil to Thailand, the satellite is visible 24 hours a day. The equipment to use it can be a bit daunting, if the experience of this amateur radio club in Norway is any indication. They used a 3-meter dish for the 2.4-GHz uplink, along with a string of homebrew hardware and a lot of determination to pull off their one contact so far, and this from a team used to bouncing signals off the Moon.

Receiving signals from QO-100 is considerably easier. A dish in the 60-cm to 1-meter range will suffice, depending on location, with a decent LNB downconverter. Pretty much any SDR will do for a receiver. An alternative to assembling the hardware yourself — and the only way to get in on the fun for the two-thirds of the planet not covered by the satellite — would be to tune into one of the WebSDR ground stations that have been set up. The British Amateur Television Club and AMSAT-UK, located at the Goonhilly Earth Station, have set up an SDR for the narrowband transponder that you can control over the web. I used it to listen in on a number of contacts between hams the other night.

It’s hard to overstate the importance of QO-100. It’s the first ham repeater in geosynchronous orbit, as well as the first DATV transponder in space. It’s quite an achievement, and the skills it will allow hams to develop as they work this bird will inform the design of the next generation of ham satellites. Hats off to everyone who was involved in getting QO-100 flying!

The $50 Ham: Getting Your Ticket Punched

Today we start a new series dedicated to amateur radio for cheapskates. Ham radio has a reputation as a “rich old guy” hobby, a reputation that it probably deserves to some degree. Pick up a glossy catalog from DX Engineering or cruise their website, and you’ll see that getting into the latest and greatest gear is not an exercise for the financially challenged. And thus the image persists of the recent retiree, long past the expense and time required to raise a family and suddenly with time on his hands, gleefully adding just one more piece of expensive gear to an already well-appointed ham shack to “chew the rag” with his “OMs”.

Not a $50 ham. W9EVT’s shack. Source: QRZ.com

As I pointed out a few years back in “My Beef With Ham Radio”, I’m an inactive ham. My main reason for not practicing is that I’m not a fan of talking to strangers, but there’s a financial component to my reticence as well – it’s hard to spend a lot of money on gear when you don’t have a lot to talk about. I suspect that there are a lot of would-be hams out there who are turned off from the hobby by its perceived expense, and perhaps a few like me who are on the mic-shy side.

This series is aimed at dispelling the myth that one needs buckets of money to be a ham, and that jawboning is the only thing one does on the air. Each installment will feature a project that will move you further along your ham journey that can be completed for no more than $50 or so. Wherever possible, I’ll be building the project or testing the activity myself so I can pursue my own goal of actually using my license for a change.

(A shout-out to Robert for suggesting this series, and for graciously allowing me to run with his idea.)

Getting Your Ticket

The licensing of amateur radio stations in the United States goes all the way back to 1912. (I’m concentrating on US laws and customs regarding the amateur radio service simply because that’s where I live; please feel free to chip in on the comments section about differences in other countries.) Anyone who wants to operate on the bands reserved for the amateur radio service has to be licensed by the Federal Communication Commission. Unlicensed individuals are free – and encouraged – to listen in on the bands, but if you don’t have a license, you can’t transmit. And trust me, the local hams, with know-how, equipment, and all the time in the world, will find you, resulting in an unpleasant encounter with the FCC.

There’s really no reason not to get a license anyway. This will be among the cheapest parts of a ham’s journey, and perhaps even free. To earn a license you’ll need to pass a written exam, but before taking the plunge you’ll need to know a little about the classes of amateur radio licenses, and the privileges they bestow.

The current entry-level license class in the US is called Technician class; the old Novice class was eliminated in 2000, along with the Morse code requirement for all classes. Technicians have privileges to operate mainly on the upper frequencies, primarily on the 2-meter (144 MHz) and 70-cm (420 MHz) bands in phone mode, which means voice transmissions. Technicians also have access to small slices of the 10-meter band using data modes, and small sections of 15-, 40-, and 80-meters if they learn Morse or use a computer to send and receive it. This limits the Technician to mainly local communications, but there’s plenty to do and loads to learn on these bands.

The band plan for US hams. Note that Technicians only have phone (voice) privileges on 10 meters and below; the long haul bands are off limits unless you use Morse. Source: ARRL.org

Practice, Practice, Practice

Even with all the limitations, a Technician license still offers access to a lot of spectrum and serves as the gateway to the next two classes, General and Extra. Everyone has to start with a Technician license, which requires passing a 35-question multiple choice examination. The exam is standardized with questions selected from a fixed pool, with topics ranging from knowing FCC Part 97 rules to basic electronics and RF theory. The exam is pretty easy, especially for anyone with a background in electronics. In fact, many complete newbies come to exam sessions after having run through enough online practice tests to see every possible pool question and pass the exam without understanding a thing about radios or electronics. There are lively debates over whether that’s a good thing or not – personally, I’m not a fan of it – but it is what it is; the Technician exam is dead easy.

Your investment in a Technician license will be minimal, and mostly consists of the time it takes to study. Online practice tests – I recommend the tests on QRZ.com – are free to take as many times as you need to. Some ham clubs offer local classes aimed at helping you to prepare, and those generally charge only a nominal fee. There are even one-day intensive “ham cram” sessions where you’re guided through all the material and take the exam at the end of the day.

Typical exam session. Calculators are allowed, but no smartphones, please. Source: Tri-County Amateur Radio Club

Exam sessions are run by Volunteer Exam Coordinators (VECs) Volunteer Examiners (VEs), hams who have special training in administering and grading exams. They too charge only a nominal fee – I think I paid $15 – and may even waive the fee under certain circumstances. There are also occasional special events like the annual Field Day, where hams set up tents and booths in public places as an outreach to the public, where exams are often administered for free.

Honestly, getting your Technician license is about as low impact as the amateur radio hobby gets. Once you can consistently pass practice tests online, the actual exam is a breeze. Exams are graded on the spot so you’ll know instantly how you did, and you can even take the next exam for no extra charge if you’re ready. Give it a shot even if you haven’t studied – I nearly passed my Extra exam going in cold after I aced my General.

Next Time

In the next installment I’ll start discussing what the newly minted Technician can do with his or her license. It may seem like a pipe dream to get on the air for less than $50, but it’s surprising what’s available these days, and you’ll find that fifty dollars can go a long way toward making your first contact.