RTL-SDR: Photography from Satellites in Orbit

An image from NOAA 18 on June 11th

Now that I've successfully applied my RTL-SDR device toward aircraft tracking and digital radio reception, my next challenge was tuning in signals from space, like Jeff Goldblum's charcter in Independence Day. As sophisticated as this sounds to someone unfamiliar with radio, and electromagnetic signals, receiving and sending data to and from space is a pretty mundane thing these days. Use GPS on your phone or in the car? You're connected to a machine floating in space. And, satellite television services have been around for decades. But, I wanted to put my RTL-SDR device and rooftop antenna to use taking advantage of some weather satellites that pass over every populated country on earth at least once per day sending real-time pictures down to anyone who'd like to view them. In a way, I would be using government weather satellites from the United States and Russia to take very, very long-range selfies.    

NOAA 19 before its launch

These satellites, the NOAA 15, 18 and 19 (from the US) and the Meteor M2 3 and 4 (from Russia) are very similar in purpose and function, and orbit at similar distances about 500 miles above Earth. They circle around the globe (sorry flat-Earthers) on a north-south path crossing the north and south poles while the earth spins below them. That way, they're able to pass over and see most parts of the earth below during a given time window -think of painting a sculpture in an up-and-down motion as it spins on a pottery wheel. As the satellites orbit, they continually take photos and measurements, and transmit them back to earth at specific frequencies (137.62 MHz for NOAA 15 and 137.9 MHz for Meteor M2-3, for example). These frequencies are just below the VHF frequencies used for HAM radio in the United States, and can be heard with an SDR device, and a lot of store-bought radios for CB, HAM and other uses. But, you'll need software to de-modulate the APT transmission, otherwise it will simply sound like static or clicking to the naked ear.  

In spite of having an antenna, an SDR receiver and some software experience with air-band radio, and ADS-B airline tracking radio, reaching a satellite proved to be fairly difficult. For one, the satellites are always moving, and you can only retrieve their signal during a ten to fifteen-minute window while they pass sufficiently overhead. Secondly, the software used for amateurs like me to locate, track and decode the satellites' signals are always changing and often out-of-date, as many of these programs are created and supported by amateur enthusiasts, and not large institutions.

NOAA 19 on Satellite Tracker

My previously helpful guidebook, The Hobbyist's Guide to the RTL-SDR proved to be out-of-date with many of its recommendations for software. I tried all of the suggested ways of connecting to NOAA (National Oceanic & Atmospheric Agency) satellites as well as the Meteor M2 (Russian Space Agency, Roscosmos) satellites in the chapter on low earth orbit (LEO) satellites, and while helpful in explaining the general process, it gave some applications and programs that simply do not work well anymore. Certain PC satellite trackers, for example, no longer seemed to provide accurate tracking for my location, and SDR++ (a great software defined radio receiver) had no way to decode the satellite's modulated signals into valuable data or images. I ended up spending a lot of time recording audible fuzz, to demodulate it into visible TV snow, or listening for a satellite that wasn't there.

I finally found some reliable software by browsing the r/RTLSDR Subreddit, a surprisingly active and supportive community of digital radio enthusiasts with a wellspring of info on satellite communication. It was clear, Satdump was the go-to free application for tracking, hearing and demodulating satellite radio signals. Where my book was offering various programs to do each part of the process, Satdump does all three for a variety of different satellites and LEO objects, including the NOAA and Meteor M2 Satellites. Additionally, I used the Satellite Tracker app on my iPhone to track satellites, verify their actual position and path with Satdump, and find out when I needed to be at my computer to record the downlink. 

My initial set-up

I had my first success when I finally timed a NOAA 15 satellite pass correctly, and started recording the correct radio frequency (137.62 MHz) on Satdump when the satellite came into range. De-modulating a signal is a little difficult for a lay-person, but a Redditor had suggested I listen for "ticking" over the airwaves as the satellite passes. Sure enough, once NOAA 15 popped up in the tracking window as a little red dot, I heard a tick-tick-tick, like an old clock, as the mass of chaotic static in the de-modulator widow started to move together in unison. I was synced with the Satellite! Satdump would start downloading images and data from NOAA 15 onto my desktop. I was using a little handheld antenna indoors, and the satellite's pass was not perfectly overhead. It was just a convenient time for me to run to my computer and set-up, so the first pictures were not great. There was a lot of fuzz where my downlink faded, due to a small antenna with poor reception indoors, but what did come out was unmistakable: swirling clouds and storms over the eastern US and Canada, with the Great Lakes visible. It looks like the Satellite had been well to the east of my receiving range when I caught its signal, but it was clearly a photo of Earth from above!

My rooftop UHF/VHF antenna

Since then, I got a Daiwa coaxial switch for my rooftop antenna, so I could use it for both the RTL-SDR and HAM radio transceiver. Plus, learned a bit more about Satdump's tuning and de-modulating options. Now I'm not only pulling visual images, but data sets with land/sea temperature and precipitation info as well. Plus, I had the opportunity to wait for some very close satellite passes overhead where the signal was the best for the longest period of time. 

Having downloaded numerous images from each of the current NOAA satellites, my next challenge is connecting to the Russian Meteor M2 satellites. There are are only two of them, and one has been either been offline or not functioning for some time. But, I did manage to get a partial image from Meteor M2-3 as of June 11th, 2024 using Satdump, RTL-SDR and my HAM antenna. It's just a mater of waiting for M2-3 to pass-over at closer range. Other challenges will be to build some new antennas specific to this type of satellite communication, as my current set-up is optimized for terrestrial amateur radio, which is likely the cause of some of the static in my images.  

Stay tuned to Cubicalruins.com for an in-depth tutorial on using Satdump to demodulate and image APT signals, as well as updates on connecting to the new generation of NOAA GOES satellites, which are a whopping 22,000 miles away from Earth. Who knows, maybe we can prepare you to save the world one day. 

Image from NOAA 15

Image from NOAA 15 with borders and shorelines colored for reference

A raw NOAA 15 image super-imposed over a flat map of Earth for reference

The Thing(s): 86 Years of Watching the Skies

The major streaming services' suggestion algorithms already know too much. I knew this the moment I logged into Netflix and it had labelled "dark Scandinavian suspense thrillers" as one of my favorite genres -not only specific, but right on the money. It couldn't be anymore specific unless it had been, "dark science fiction thrillers that take place on remote polar research bases." If it's about Antarctica or sci-fi, I'm watching it; if it's got both, it's an instant favorite. And the best example of the genre is undoubtedly The Thing, or more appropriately, The Things since there have been at least three major cinematic adaptations of John W. Campbell's 1938 novella "Who Goes There?", where "The Thing" makes its first terrifying appearance in literature. 

Campbell's story, originally titled "Frozen Hell," follows the researchers and crew of an Antarctic research station who stumble upon a crashed alien spaceship frozen under the ice. They recover a presumably dead alien body from the craft. They take the frozen specimen back to base for an examination, as any curious scientist would, and terror ensues. As a piece of sci-fi literature, it was an early example of the Golden Era of Sci-fi, from the 1930's through the 1950's, which spawned a variety of famous sci-fi books, television series and radio shows, and often prompted UFO hysteria, both real and imagined. Some sci-fi works, like Star Trek focused on the wonders of the beyond, and the shining possibilities of a space-traveling future; others, like "Who Goes There?" fall into the category I like to call "don't go to space." 

The first film adaptation of Campbell's story premiered in 1951 as The Thing from Another World. It's kind of cheesy by today's standards, but is actually quite a bit more entertaining than a lot of the sci-fi films of the day. It combines snappy dialogue with a continuous level of suspense without a lot of unnecessary filler. Parts of the film, shot at Glacier National Park in Montana are visually beautiful even in black and white. They help to capture some of the isolated vastness Campbell may have been going for in "Who Goes There?".  

At first, The Thing from Another World follows the same premise of Campbell's story, except the research base in Antarctica is replaced by an Air Force base in northern Alaska. Aviators from the base are called out to investigate a crashed object. They find a frozen alien, just like in the book. Once they return back to base with the alien encased in a frozen ice block, the terror begins. This is where, I think, The Thing From Another World begins to fall short... 

The airmen, civilian scientists and one journalist, grab guns, form a posse, hunt down and kill the alien, which turns out to be a giant vegetable (seriously!). 

There are other non-plot related criticisms as well. The first is that the one thinking intellectual in the crew of macho-man-alien-hunters, Dr. Arthur Carrington played by Robert Cornthwaite is portrayed as an effeminate weirdo who wants to (gasp!) communicate and (double gasp!!) learn from the alien, before killing it. He tries to do so, and gets immediately crushed on queue, making way for the capable heroes of the US military to save the day. Also, the only female cast member (the scientist's assistant), played by Margaret Sheridan, has very few lines, the longest of which is to suggest that a vegetable can be killed "lots of ways," by broiling it, grilling it, steaming it, etc.

But let's not get too intellectual. This pulpy flick isn't meant to be a thought-provoking piece of weighty philosophy; it's about a SPACE MONSTER after all. The real fault in Thing From Another World isn't the 1950's sexism, or the thinly veiled, Cold War-era, anti-intellectual McCarthyism (all movies from that time had some of that, especially the sci-fi ones). It's that it took away The Thing's most terrifying feature, its ability to shape-shift into any human it comes in contact with, and hide in plane sight until it's time to kill.

The Thing, the second cinematic adaptation of "Who Goes There?," premiered in 1982. Directed by legendary horror and sci-fi director, John Carpenter, and starring a great cross-generational cast including Kurt Russell, Wilford Brimley, Donald Moffat and Keith David, was neither a commercial success or failure, and it was panned by early critics as grotesque, nihilistic and boring. However, The Thing grew to be a cult classic, and in my opinion, a sci-fi horror on-par with Ridley Scott's Alien. 

The first scene capitalizes on the source material's setting with breathtaking areal shots of the white "Antarctic" wilderness (though the filming took place in Juneau, Alaska). A helicopter with "NORGE" (Norway) painted on it tracks a stray sled dog across the ice. We see one pilot manning the chopper, and another load a rifle and take aim from the aircraft as it approaches the galloping husky. A simple, but suspenseful monotone bass score, by composer Ennio Morricone, booms as the airborne hunters try once, and again to put the desperate dog down. The scene, with no dialogue and no prologue, brilliantly captures a “what-the-fuck is happening?” feel that entices viewers to stay seated to find out what is in store. Where-the-fuck are we? Who-the-fuck are they? and Why-the-fuck are they shooting at an innocent animal? Before the Norwegian hunters can stop their prey, it finds shelter at a structure, US Outpost 31.  

Conflict ensues when the American crew of Outpost 31 defends the seemingly innocent animal. The Norwegians, desperate to kill the dog, fire toward the American defenders. Gary (Moffat), the armed commander of the Americans fires from behind a window and kills the apparently crazed Norwegians. 

"First goddamn day of winter," says R.J. MacReady (Russell), the American chopper pilot for the station.

Not long after Outpost 31 loses contact with the outside world amidst an incoming blizzard (because of course), the crew finds out why these Norwegians did not want that dog to escape. It was no dog at all, but a creature, something horrendous. Once locked in the shelter with the other sled dogs, it reveals its gruesome form, digesting the terrified animals one-by-one with its array of tentacles. Members of the crew are there to witness the attack and kill the hideous thing before it can get away, but the danger remains... if The Thing can imitate a dog perfectly, it can imitate a human. The dog has been walking freely around the outpost since it was rescued; it could have eaten any member of the crew, and still be hiding among them. No one could be trusted. 

Just like in the original story, the Scientist, Blair (Brimley) is the first to crack from the terror. Or, maybe, he just saw the writing on the wall before anyone else did: The Thing could not be allowed to leave, and neither could anyone else. If it made it to a populated area, it will begin to eat and imitate everyone on earth, no one would be prepared, no one would see it coming. Before he's subdued by the rest or the crew, the frantic scientist destroys the radio equipment further isolating Outpost 31 from any rescue. From that point forward, with no way to tell who is real and who is an alien imposter, the crew's worst enemies are themselves. One after another, a crew mate deemed to be "infected", a talking, begging, desperate copy of someone who used to be friend, is shot to death or burned alive by the humans left on the station. The surviving crew's trust in one another fades as their fear rises. Soon, it's every man for himself, as no one really knows who the real Thing is anymore. "Frozen Hell" indeed. 

Carpenter's 1982 version of The Thing, has some dated special effects and admittedly has its dry spells, where suspense turns to boredom. But, for the most part, it really captures the vast loneliness of Antarctica with the intimate claustrophobic nature of the base. With nowhere to run, and no one to call for help, the crew of Outpost 31 may have well been on a spaceship, with an Alien crawling around in the ventilation shafts. It's sci-fi horror at it's finest. 

The Thing (1982) has certainly outlasted early criticism, remaining a pop-culture phenomenon to this day. A fairly good prequel based on Carpenter's 1982 film was released in 2011, staring Mary Elizabeth Winstead and Joel Edgerton. And, most notably, the online video game sensation Among Us, based on the premise of an alien imposter infiltrating a space crew debuted in 2018, and it soon had a cooped-up COVID-weary public on their phones, PC's and Nintendo Switches trying to guess which player was the "imposter", spacing many an innocent teammate in the process. In fact, The Thing is screened every year by the real-life crew of the Amundsen–Scott South Pole Station at the beginning of Antarctic Winter. Scientists have weird sense of humor. 

John Carpenter clearly knew what he was doing when he picked up this screenplay adapted from that early Novella called "Who Goes There?". The themes of The Thing are timeless, they transcend the sci-fi gerne all together, eliciting even the classic transcendental literature of writers like Edgar Allen Poe and Henry James. It may say more about the dangers of humans, than any space monster. Like Poe's "Tell-Tale Heart," or the phantasm in James' "The Turn of The Screw," we could easily dismiss any survivor's account of coming in contact with The Thing as a paranoid delusion, an insane fantasy, the natural result of being cooped-up and isolated on a remote polar research base where the sun doesn't rise for a month. Furthermore, we could look at The Thing as a reflection of post-modern society. With misinformation filling the airwaves, claims of "fake news" being spewed out by all sides of the political spectrum, artificial intelligence mimicking human interaction, and sometimes even humans themselves, a shapeshifting demon seems like an apt metaphor for the times. Heck, if a malicious adversary wanted to create chaos, they need only convince their enemy that A Thing is among them, and watch as paranoia and fear tear them apart from within. Perhaps this has already been tried.

The 1951 film, The Thing From Another World, may have fallen short of the mark when compared to Carpenter's 1982 remake but it does have a memorable quote at the end. After the alien is defeated, the journalist, "Scotty" (played by Douglas Spencer), who witnessed the battle, addresses the public by radio... 

"And now before giving you the details of the battle, I bring you a warning: Everyone of you listening to my voice, tell the world, tell this to everybody wherever they are. Watch the skies. Everywhere. Keep looking. Keep watching the skies." Maybe he should have added, keep watching each other too. Anyone, anywhere could be The Thing.  

Campbell, John W.  "Who Goes There?" in Astounding Science Fiction Magazine. Street & Smith, Publications, Inc. 1938.

Nyby, Christian. The Thing From Another World. Winchester Pictures Corporation, Los Angeles, California. 1951. 

Carpenter, John. The Thing, Universal Pictures, Los, Angeles California. 1982.  

Radio Check: Repeaters & Range Testing

As I discussed in my previous article, I successfully installed a much larger antenna for my HAM radio base station, but due to my schedule I wasn't able to really flex my HAM muscles outside of a few basic tests: the SWR for the new antenna was good, and I was able to connect to a few repeaters slightly outside of the range of my old mono-pole mobile antenna. So, this week I hopped on Chirp and went about testing the full power of the upgraded station. 

Using Chirp, a programing application for radios and scanners, I downloaded lists of repeaters within 25, 50, and 75 miles of my location in northeast Ohio. Chirp is a great resource for HAMs and radio enthusiasts, as it allows users to download lists of frequencies from a variety of sources which are updated daily and filter based on your preferences. I used the query source from RepeaterBook, a listing of all known HAM repeaters in the United States and abroad, and pulled in all the repeater frequencies for the 2 meter and 70 centimeter bands on which I'd be transmitting. Chirp provided a list of more than 100 repeaters within listening range of my station, their sub-audible tones and general information about their locations. I began going down the list, which stretched across most of northeast Ohio on into Pennsylvania, and made radio checks for each repeater, to see if I could get a "hit" or hear a response. The image above shows a sampling of repeaters I  hit while testing. The range of my station alone, without the additional boost of a repeater's relayed transmission, is more than 50 miles, so I was quite happy with the result.

If you've already read my previous articles, you'll know that repeaters are automated transceivers HAMs use as relay points. They use a "duplex" receiver and transmitter to listen for transmissions on one frequency then beam them out on another, often across a much farther range than what the original transmission would otherwise carry. Because repeaters are always in the same location, and often have courtesy tones, or beacons, which let listeners know their transmission has been heard, they make ideal testing frequencies, rather than using a person-to-person "simplex" frequency where another person must be present to hear and respond to a radio test. Transmitting to a repeater also increases the chances that another HAM operator will hear your radio check and respond with feedback about their location and how well they heard you, which is really exciting! 

The task however, like a lot of work in radio and signal testing, is a long and somewhat tedious process. For one, while RepeaterBook strives to keep their record as up-to-date as possible, some frequencies are bound to be out-of-date, repeaters may only be re-transmitting at certain times, and others may not have a tone or beacon which will clearly confirm that you've hit it. In may ways, the testing process is like walking blindfolded, until you find something. But, finding something is quite rewarding when it happens. It's always great to hear the "beep", Morse code beacon, or recording from a newly discovered repeater and recording a new active frequency in your log. Below is an example of a repeater response from W3LIF near New Castle, Pennsylvania. 

Sometimes I stumbled across a conversation, or a full-blown "net" which is kind of like a HAM radio call-in show, with people who check-in and talk at scheduled times each day. Sometimes, the same group of people will keep in touch via nets regularly for many years. One net I stumbled across while testing had 47 HAM operators check-in on one night, so the HAM community in northeast Ohio is alive and well.  

But, by far the most rewarding experience, is connecting one-on-one with other people. In my first week of testing I connected with a handful of individuals, from Wadsworth to Youngstown (Home of the YSU Penguins), who heard my transmissions and responded to my radio checks. Not only is it great to make a new contact, it's good to know that your transmission was heard loud-and-clear by a real person in a certain location. Most of the time the other HAM operator is happy to spend a few minutes providing feedback on your signal. For example, they can let you know if your signal is clear or garbled, to give you an idea of whether you can transmit with low, medium or high power to reach a certain location clearly. My particular radio can transmit at 50 watts, which at full power, uses a considerable amount of energy and can even make the radio and antenna hot to the touch, or even interfere with other devices near the transceiver -like a Bluetooth stereo. (FYI: a ferrite choke will limit interference like this even at high power outputs. That's the answer to question G4C08 on the General License exam question pool, by the way).

There are a lot of factors that can impact signal propagation, including the transmitter location, the location of the receiving antenna -whether it's high atop a hill, tower, or city sky-scraper, etc.- physical barriers -such as hills, mountains, etc.- and the availability of a receiving counter party, human or otherwise, to confirm receipt of your message. But, in one week of testing, I've been heard as far as 54 miles out, without the help of any signal boost from a repeater's output transmission. With the help of the repeaters on my own signal's frontier range, I estimate I can probably be heard clearly on the 2M and 70CM bands around 100 miles in all directions, covering an area of over 28 thousand square miles across parts of Ohio, Pennsylvania, West Virginia and even southern Ontario. 

I will continue to test that frontier and see just how far I can potentially transmit beyond that boundary. I did hit a repeater in Lisbon, Ohio roughly 35 miles southeast of my location using only low power, which suggests my range could be even greater than the images I've included here. 

I'll stick to my 2M and 70CM band with the antenna I have for now, and continue to make to contacts in northeast Ohio and surrounding areas. However, as I continue to invest in the hobby, many more challenges await such as transmitting to orbiting satellites, or even the International Space Station -both can be done with my current equipment and technician's license. And, as I get even more advanced, I can even try using a shortwave antenna on the 20M band, which can basically transmit world-wide!

KD9ZDY Gets a New Antenna

Since earning my technician's license this past fall, I've basically just been listening in to various HAM frequencies, scanning for signals and learning about my equipment. In spite of passing my exam, there was still a lot I felt I needed to know before really getting started. Beginner's anxiety generally kept me away from transmitting with my call sign, and even when I did try, I found that my limited antennas (handheld "rubber duckies") were not really well-tuned enough to generate an audible signal that would travel more than a few miles. Even if there were some other HAM operators in my listening range, it wasn't likely they'd be able to hear me unless they were tuned-in right at the same time I was transmitting, and also within a short distance from my location. I could listen in on signals as far as 100 miles out, but I could not transmit that far. I needed a bigger antenna, something to really put my 50 watt ICOM IC-2730a transceiver to work. 

So, I began my latest HAM project: installing the telltale antenna -the ones that easily identify the radio enthusiasts in your neighborhood, and sometimes run afoul of the maligned home owners' association. I ended up buying a 2-meter and 70-centimeter band antenna from HYS. This fiberglass antenna had good reviews, and is basically a slightly less-expensive copy of the similarly tuned name-brand Comet antenna, which has a good reputation in the radio industry. The HYS is white and flexible, so it blends in nicely with the front of my house, and it should hold up to heavy Midwest winds. Outside of the good reviews, and attractive price point, I chose this model because it's tuned for the 2-meter and 70-centimeter bands which are the most common frequency ranges for local FM HAM communications. The length in meters and centimeters, is roughly equal to one wavelength between 144-148 MHz "2m" band and 420-450 "70cm" band. The 5-foot, 7-inch pole with three steel radials at the base is perfectly tuned to transmit at the 2m and 70cm frequency ranges. The HYS also boasted a 1.5 standing wave ratio (SWR), meaning it was well-suited to provide the most gain (signal strength) for the 50 watt power output that my transceiver was capable of providing. An SWR that is too high can cause damage, as too much of the power pushed into an antenna will feed back into the radio. An SWR of 1.5 or less means that the antenna is sufficiently resonant to safely transmit. But, I'd still need to install and test the antenna to make sure it works as advertised. 

Before the tough business of mounting the antenna and wiring the it to the base station, I first connected my a hand-held Baofeng UV-5R transceiver to the antenna to make sure it wasn't blatantly faulty. I dialed up the input frequency for my local repeater, and listed for its response "beep" on the output frequency. Sure enough, I heard the beep. So, at the very least, the HYS antenna would be as good as what I was already using. 

Set-up was actually quite straight-forward. I only needed a mount, a lightning arrestor, grounding rod, and about 30 feet of all weather HF coaxial cable, plus some siding hooks and wire clips to run the the wire neatly around the back of the house and in through the basement window where my radio is. I chose this location and set-up as a compromise between getting the antenna as high as possible without drilling into my home's plastic siding, and being able to install the antenna, and potentially remove it safely, without having to climb onto the roof. You can see from the photo above that a person can easily access the antenna from the front porch without a ladder. The other main safety precaution was adding a lightning arrestor and ground rod near the point where the cable enters the back of the house. The 4-foot copper rod is buried straight down 2-feet from the base of the house with three, 4-foot copper radial wires extending away from the home to disperse any charge from a lightning strike. 

Now it was time to test station KD9ZDY's new antenna with the real transceiver from the comfort of my basement HAM "studio." First, I wanted to make sure the antenna has a safe SWR of 2 or less as advertised, before transmitting. For this, I used my handy NanoVNA network analyzer. Success! The analyzer, calibrated to measure SWR between 100 and 500 MHz, shows two deep troughs at the 144 and 420 MHz ranges where the ratio dips below 1.5. So, the antenna came as advertised and is safe for my transceiver to transmit on the 2m and 70cm bands.

The final step was to get on the air and announce myself with a radio check to see if anyone or anything could hear me. Success again! While I didn't immediately hear from any other HAM operators, I could hear the beacon, or courtesy "tone", from repeater antennas I'd never been able to contact before. Repeaters, automated transceivers, which listen for your transmission and repeat it over a much longer range often send a beacon, tone or squelch tail (the static fuzz that denotes an end of transmission), if it successfully receives a transmission. In the video above, you can hear the repeater's beacon when when I made contact with it. Not long after confirming my station's new capabilities, I was getting responses from other HAMs across the region, confirming that they got my signal loud and clear.

RTL-SDR: Home-made Air Traffic Control

If you've read my previous article, "Flight Tracking: I Guess I'm a Plane Guy Now...", you're well aware of my interest in air traffic control (ATC) and flight tracking. If you look to the right of the Cubicalruins homepage, you'll even see my embedded flight tracking window from FlightRadar24.com, my favorite flight tracking website. But, radio -and specifically SDR- allow me to take my hobby a step further. Rather than depending on web-based flight tracking websites, I'm now able to run my own air traffic control system from home. 

A screenshot of RTL1090 and Virtual Radar Server on my PC

Anyone involved in aviation or flight-tracking will already know this, but air traffic controllers and airport towers used to use radar to identify incoming and outgoing planes. But now they primarily use unique transponder (radio) signals from each individual aircraft to identify and track all flights. The most commonly used transponder system is the Automatic Dependent Surveillance Broadcast (ADS-B) system which broadcasts on 1090 MHz, and some smaller aircraft use a Universal Access Transceiver (UAT) system, which broadcasts on 978 MHz. While radar is still used as a secondary tracking system by both military and civilian air controllers, the ADS-B and UAT systems now allow a hobbyist like myself to pull actual, real-time flight data from the planes, helicopters, blimps and sometimes weather balloons directly to our PCs. Using SDR, we can see everything the FAA air traffic controller sees.       

In my previous article I discussed setting up and testing my RTL-SDR dongle and antenna to pull AM and FM voice radio into my PC. This was a pretty simple initial test. But, getting ATC signals into the PC, decoding them, and plotting the data onto a viewable air-traffic map was considerably more difficult. In the end I was able to run the RTL-SDR with two different ATC/plane-tracking applications, PlanePlotter and Virtual Radar Server. Both provided challenges, but after multiple troubleshooting attempts I got both systems up and running. 

Using Carl Laufer's "The Hobbyists Guide to the RTL-SDR," I started my my home-made air-traffic control project. Page 67 provides a brief intro to plane tracking on the RTL-SDR; page 69 describes how to download and install Dump1090, a primary decoder of ADS-B data from 1090 MHz; page 72 provides instructions on installing RTL1090, another decoder; and page 75 describes how to install and use PlanePlotter, an application for viewing the planes on a map. While the instructions were very useful, I did run into a few hitches along the way, and I'm not sure if these were due to my Windows 11 operating system, outdated versions of the software, or my own lack of knowledge on PC's -normally I use a MAC. However, I'll try to provide some helpful step-by-step guidance at the end of this article for SDR enthusiasts hoping to run Planeplotter or Virtual Radar server.

The F-14 "Tomcat" on display at the MAPS Air Museum in North Canton, Ohio

My first hitch was that the suggested decoding software, Dump1090, simply did not work on my PC. My command console just did not recognize the command "--net-ro-port 30002 --net-beast" when added to the dump1090.bat file necessary to run the decoder. I'm still unsure why. Thankfully, Laufer's book had an alternate suggestion for a decoder, RTL1090, which I downloaded from Jetvision at https://rtl1090.com/. The funny thing is RTL1090 didn't work either until certain dll files such as rtlstr.dll were also installed; and guess which zip file had exactly the dll files I needed? The dump1090 zip! So, regardless of which decoder you use, I'd recommend downloading both RTL1090 and Dump1090, the IMU version and source code, and extract them into the same folder. That way you'll know you have all the dll files needed to run each application. Ultimately, I was able to successfully install and run RTL1090. 

My next challenge was installing a program to visualize the data from RTL1090. I downloaded Planeplotter at https://www.coaa.co.uk/planeplotter.htm as well as Virtual Radar Server at https://www.virtualradarserver.co.uk/. Both were easy to download and install. But, I should mention, PlanePlotter requires a one-time 25 Euro (roughly $30 USD) license fee and software registration if you plan to use it beyond the two-week free trial period. The next step is to set up your new visualization apps to accept the ADS-B data from your antenna and decoder. You must set up your decoder (RTL1090 or Dump1090) as a TCP/IP client in the options menus, using port 30002 for Dump1090, or 31001 for RTL1090. Once the correct port is saved in the options, and you begin running the application, you should see planes flying in your app! 

My home ATC set-up with RTL-SDR dongle and antenna

After all this, the results were well worth the effort. I've always been fascinated by air travel, and the complexities of keeping all those thousands of aircraft above our head safely moving. The ADS-B signals on 1090 MHz is a big reason why this is possible. Plus, I live very close to the Kent State University Airport home to the FedEx Aeronautics and Academic Center; there are always maybe 1 to 6 little KSU aircraft buzzing over our heads at any given moment pinging their data to 1090Mhz. So, there is always something to watch. Additionally, not only am I using a web-based app to see aircraft, but now I'm an actual contributor to these sites, providing my own flight data to help others see planes over my reception area.      

I've done my best to provide quick step-by-step tutorials on each set-up below. 

RTL1090

1.) Go to RTL1090.com and download the IMU version of the software.

2.) Go to https://github.com/MalcolmRobb/dump1090 and download the zip file for the application. Extract all files into the same single folder as the RTL1090 IMU. 

3.) Install and run RTL1090. If any dll files, such as rtlsdr.dll, are missing, search the directory at the url in the previous step for those files and add to your single extracted file for dump and rtl1090. 

4.) Once installed, open RTL1090 and click "start," if your RTL-SDR is plugged in and connected to an antenna you should see numbers scrolling in the List tab. This is the raw ADS-B data coming from 1090Mhz. You're all set!  

5.) [Optional] Download and extract all files for the RTL1090 "Scope" version from RTL1090.com, and run this version if you'd like to see the Scope and Plug-in tabs in the newest "beta" version of the application. 

NOTE: I was unable to connect RTL1090's IMU or standard versions with Planeplotter. For some reason, the RTL1090 "Scope" version worked. Plus the Scope version has it's own small visual aid with planes and headings as well.

RTL1090 + Virtual Radar Server 

1.) Follow steps one through five above. 

2.) Download Virtual Radar Server at https://www.virtualradarserver.co.uk/Download.aspx. 

3.) Open Virtual Radar Server, then go to Tools > Options. Click Receivers, and click the plus (+) icon to add a receiver. Name the new receiver RTL-SDR (or whatever you choose). 

4.) Make the data source "AVR or Beast Raw Feed."

5.) Keep the IP address 127.0.0.1. Make the Port: 31001 for RTL-SDR. (It should be 31001 even if your RTL1090 window says 31011.)

6.) Click start on RTL1090 and have it running in a different window. Then click the http://127.0.0.1:8081/VirtualRadar link in the middle of the Virtual Radar Server window. In the browser, you should see planes within receiving range of your antenna. You're all set!

7.) [OPTIONAL] In Tools > Options you can click on Receiver Location and enter your coordinates to save your current location. The next time you open your browser map, it will automatically center on your location. 

RTL1090 + Planeplotter

1.) Follow steps one through five under the RTL1090 instructions above. 

2.) Download and install Planeplotter at https://www.coaa.co.uk/planeplotter.htm, and open the application. 

3.) [OPTIONAL] When prompted, you can register your download and pay for a lifetime license through PlanePlotter's payment service. Once the payment is made, you'll get an email at the registered email address with the registration confirmation code which is good forever. Otherwise, skip this step and simply use the free trail. 

4.) [OPTIONAL] When prompted, enter your current coordinates to set your location on the map.

5.)  In PlanePlotter, go to Options > Mode-S Receiver > AVR Receiver > TCP/IP Client. Make the address and port 127:0.0.1:31001. (Again, even if your RTL1090 window shows the port as 31011). 

6.) Go to Options > I/O Settings and check MODE-S/ADS-B. Then, click AVR Receiver TCP and OK. This will set your RTL-SDR up as a TCP/IP client. 

7.) In the main window, click the green circle and make sure RTL1090 is running in another window. You should see planes on your map. You're all set! 

8.) [OPTIONAL] Obtain a MapQuest API key at https://developer.mapquest.com/documentation/ by clicking "Grab the key." You may need to create an account with developer.mapquest, but the API key is free. 

If you enter the Mapquest API key in Options > Charts under the Mapquest option, and save, you can download a more detailed map to view beneath your planes by holding the right Shift key and clicking the globe or "MAP" buttons in the toolbar of the main PlanePlotter window. The stock map is very, very, basic. 

NOTE: For some reason, I could only get the Mapquest chart to work by holding the Shift key and then clicking the MAP button. 

"The Hobbyist's Guide to the RTL-SDR: Really Cheap Software Defined Radio." Fourth Edition. (2024), Carl Laufer.

RTL-SDR: Decoding Radio Signals on your PC

"They have the radio on computers now?" That was my first thought when I learned about Software Defined Radio (SDR) after I started studying for my HAM radio license exam. It was one of the more interesting tidbits I passed over while hitting the main question pool info such as antenna set-up, band plans, basic circuitry etc. But, it intrigued me. It was one area where HAM radio has taken a leap forward, providing inexpensive access to digital signal decoding to learners and hobbyists.

My PC showing SDR# software

Home SDR for hobbyists got a big boost in 2012 when Realtek launched the RTL-SDR dongle; it's a USB plug-in about as big as a "fun"-sized Halloween candy. One end plugs into your PC's USB port, and the other side has a coaxial connection that can be fixed to an antenna, or antenna system. Once the RTL-SDR is installed with all the drivers, and attached to an antenna, it will immediately begin feeding radio signals from the air to your PC. 

The big difference between SDR and most PC radio applications is that sound is not simply being streamed through your internet service provider, it's actually being picked up from the airwaves flying around you every second of everyday. You can un-plug your Wifi or data connection, and the RTL-SDR will still pick up those radio frequencies. It can even listen for, and decode, signals no normal PC or radio would ever get such as the amateur radio bands, nautical communications between boats and ships, and ADS-B and UAT transponder data from all aircraft both large and small. None of these signals are encrypted, and it's perfectly legal for hobbyists to listen in, provided they do not transmit on these frequencies in a way that could disrupt normal communications. 

The RTL-SDR dongle & antenna 

When I first unpacked my RTL-SDR and antenna set, which I ordered at RTL-SDR.com for roughly $60 USD including all components and shipping, I didn't quite know where to start. So, I also ordered The Hobbyist's Guide to The RTL-SDR by Carl Laufer as my starter guide. The book is a well-indexed set of step-by-step tutorials and trouble shooting techniques combined with general information about SDR and the various signals hobbyists can decode. Page nine discusses the initial installation of the RTL-SDR dongle, its drivers, plug-ins, and port numbers; page 13 provides a step-by-step tutorial on SDR# (or SDR sharp), a basic application for decoding, viewing and listening to signals received by the dongle. 

After a few read-through's, I was ready to test my new set-up. For my first test, I decided to get the daily weather. I tuned my SDR# app to 162.400 MHz, the frequency for NOAA Weather Radio for Akron and inland northeast Ohio, and it worked! I used my RTL-SDR to get weather (in possibly the most complex way possible). 

But, the test was a success. I could not only hear the weather report clearly, I could see all of the RF and modulation info-graphics necessary to locate and tune lots of different voice broadcasts and data transmissions. In the video above you can see the graph peaking at exactly 162.400 MHz, the NOAA station for Akron. The smaller peak just to the right is 162.550 MHz, the weather station for Cleveland and the Lake Erie shore. Both are in listening rage of my little antenna, but the higher peak is the closer signal. The digitally decoded graphics, and filtering options offered by RTL-SDR and SDR# are the perfect addition to any HAM radio base station. 

"The Hobbyist's Guide to the RTL-SDR: Really Cheap Software Defined Radio." Fourth Edition. (2024), Carl Laufer.