Tagged: rtl-sdr

MEMESat-1: A Meme-Beaming Cubesat Currently In Development

The Mission for Education and Multimedia Engagement Satellite (MEMESat-1) is planned to be the first meme broadcasting cube satellite ever created. If you aren't down with modern slang and are not familiar with the word "meme", that may be because although first coined in 1976, the modern definition was only added to the Webster-Miriam dictionary in 2015. In the traditional sense a meme is a cultural idea, behavior, style that people can't help but want to share because of how funny/amusing/interesting it is.

But in particular MEMESat-1 wants to broadcast from space the new type of meme definition, which is essentially funny or amusing images/GIFs that internet users and especially youth like to modify and share online through social media. Memes have become a major part of internet youth culture, so this could be an excellent way to speak the language of the next generation and get them interested in space, satellites, amateur radio and building satellite ground stations.

At the moment, the team hopes to launch the satellite by late 2021, and no later than Spring 2022. The satellite will be a cubesat with flash memory containing thousands of meme images that will be broadcast to Earth via a transmitter operating in the UHF 70cm radio band. Enthusiasts on the ground will be able to receive the meme images with a Yagi antenna and we anticipate that RTL-SDRs will be a commonly used receiver. The satellite will also contain an FM UHF/VHF repeater operating in the amateur radio band for ham radio use.

MEMESAT-1 is being developed by letsgo2space.com, a non-profit trying to increase the exposure kids have to STEM topics. Over on Reddit, the founder explains his story and mission:

I went out and started a nonprofit organization, built a website, developed a meme-related anxiety disorder, and am now building a meme-beaming satellite with a group of undergrads at UGA and some industry sponsors. And it’s all for the sake of making a novel meme. We are now fundraising to launch MEMESat-1.

For those who are interested in reading about the trials and tribulations of a 22 year old man-child trying to send memes into space, I’ve included the longer story below.

For my whole university career, I was in search of different work opportunities and internships to see what felt the most fulfilling and to get some of those sweet sweet resume lines. I’ve interned at a plastic factory, the Air Force Research Labs, NASA JPL, and Ball Aerospace. They were all great places filled with awesome people and cool work, but I didn’t feel connected with my work in a way that fulfilled me. So, for the past 3 years me and my buddies have been joking around about building a satellite that beams down memes from space.

Enter MEMESat-1.

While I was working at JPL, me and some buddies got together to toy around with space start-up ideas. We joked more about MEMESat, and bought the memesat.com domain back in 2018. Due to timing and other life events the start-up idea kind of fell off. One of my pals is pursuing his Ph.D, and the other is working as a spacecraft engineer full-time. I on the other hand, still had 2.5 years of school left.

Work on the MEMESat concept slowly came to a halt by the end of 2018, but picked up again in Spring 2019 when I came up with the acronym the Mission for Education and Multimedia Engagement Satellite (MEMESat-1). I kept telling my classmates and friends about the project idea as a joke, but they thought I was being serious and told me to go for it. By May 2019 I had worked out a deal with some universities to use their space, and began building the website. Over that summer, my job left me some spare time, so I started ramping up the social media for MEMESat-1 by posting daily spacefacts to instagram. I also worked on some preliminary design studies to see if the mission would be feasible, and decided that it definitely was. I also spent the summer researching how to form a company, and what the best company structure would be.

In August 2019, I returned to school and began to work on forming a company. Some great profs at GT gave me the advice to start a nonprofit, so I searched for some pro bono legal advice on starting a nonprofit. I took some of the lawyer’s advice and found some willing Directors for the company, and filed to form a nonprofit corporation - called Let’s Go to Space, Inc.

Around that time, I posted to reddit and got a bunch of attention from you guys, so I figured I should work my hardest to make it happen. I spent months emailing every space related company I could find or even think of. I have much more respect now for people that lead telemarketing campaigns, because it is really hard to convince random people over the phone/email to give you large sums of money. Now, I am happily partnered with Ball Aerospace and sponsored by Blue Canyon Technologies. I’m also in talks with some launch providers about a free launch and some help launching my lesson plans/experiment kits to classrooms all over!

We have passed the point of no return and have nowhere to go but upwards. My parents are confused and slightly disappointed that their rocket scientist son has given up any sort of salary in an effort to appease his ‘internet friends’. God bless you magnificent weirdos for keeping me going. Ad Astra Per Memes.

Currently letsgo2space is fundraising and looking for $30,000 to fund the launch of MEMESAT-1. You can either donate any amount or submit a meme for their broadcast database for $1.69 via their website.

MEMESat-1 Logo
MEMESat-1 Logo

Driver Patch for FC0013 RTL-SDRs Improves UHF and ADS-B Performance

Thank you to Benjamin Larsson for submitting news about a FC0013 tuner patch he's submitted for the Osmocom RTL-SDR driver code. FC0013 based RTL-SDRs have been relatively unpopular due to the reduced tuning range of only 22 - 1100 MHz, compared to the larger 24 - 1766 Mhz range provided by the R820T2 chip. However, they have been found in some cheaper units.

Benjamin's patch reportedly improves UHF performance above 862 MHz, and also seems to make ADS-B reception usable.

The patch was submitted to the Osmocom GitHub, however, this Git is not monitored as Osmocom have their own patch submission system via mailing list. But if you have a FC0013 dongle and want to try it, the entire change consists of only a single register value change which could easily be manually modified in the driver code before compilation. 

Register change to improve UHF performance on FC0013 RTL-SDR dongles.
Register change to improve UHF performance on FC0013 RTL-SDR dongles.

Cheap and Easy Hydrogen Line Radio Astronomy with an RTL-SDR, WiFi Parabolic Grid Dish, LNA and SDRSharp

We've recently been testing methods to help budding amateur radio astronomers get into the hobby cheaply and easily. We have found that a low cost 2.4 GHz 100 cm x 60 cm parabolic WiFi grid antenna, combined with an RTL-SDR and LNA is sufficient to detect the hydrogen line peak and doppler shifts of the galactic plane. This means that you can create backyard hydrogen line radio telescope for less than US$200, with no complicated construction required.

If you don't know what the hydrogen line is, we'll explain it here. Hydrogen atoms randomly emit photons at a wavelength of 21cm (1420.4058 MHz). Normally a single hydrogen atom will only very rarely emit a photon, but the galaxy and even empty space is filled with many hydrogen atoms, so the average effect is an observable RF power spike at ~1420.4058 MHz. By pointing a radio telescope at the night sky and averaging the RF power over time, a power spike indicating the hydrogen line can be observed in a frequency spectrum plot. This can be used for some interesting experiments, for example you could measure the size and shape of our galaxy. Thicker areas of the galaxy will have more hydrogen and thus a larger spike, whereas the spike will be significantly smaller when pointing at empty space. You can also measure the rotational speed of our galaxy by noting the frequency doppler shift.

The 2.4 GHz parabolic WiFi grid dishes can be found for a cheap at US$49.99 on eBay and for around US$75 on Amazon. Outside of the USA they are typically carried by local wireless communications stores or the local eBay/Amazon equivalent. If you're buying one, be sure to get the 2.4 GHz version and NOT the 5 GHz version. If you can find 1.9 GHz parabolic grid dish, then this is also a good choice. Although we haven't tested it, this larger 2.4 GHz grid dish would probably also work and give slightly better results. WiFi grid antennas have been commonly used for GOES and GK-2A geosynchronous weather satellite reception at 2.4 GHz with RTL-SDRs as well and we have a tutorial on that available on our previous post.

[2025 Update: With post-COVID inflation, the prices of these dishes are quite a bit higher now. You might also want to consider our new Discovery Dish product, which is a dish + 1.42 GHz feed + filter + LNA all in one.]

These dishes are linearly polarized but that is okay as hydrogen line emissions are randomly polarized. Ideally we would have a dual polarization (NOT circular polarized) feed, but linear appears to be enough and is much simpler. In addition, the 2.4 GHz feed is obviously not designed for 1420 MHz, but just like with GOES at 1.7 GHz the SWR is low enough that it still works.

The animation below shows a hydrogen line "drift" scan performed with the 2.4 GHz WiFi dish, an RTL-SDR Blog V3 and a NooElec SAWBird H1 LNA. The scan is performed over one day, and we simply let the rotation of the earth allow the Milky Way to drift over the antenna. The Stellarium software on the left shows the movement of the Milky Way/galactic plane over the course of a day for our location. The dish antenna points straight up into the sky, and we have set Stellarium to look straight up too, so Stellarium sees exactly what our dish antenna is seeing.

 

You can clearly see that there is a lump in the radio spectrum at around 1420.40 MHz that grows when parts of the Milky Way pass over the antenna. This lump is the hydrogen line being detected. As our Milky Way galaxy is filled with significantly more hydrogen than empty space, we see a larger lump when the antenna points at the Milky Way, and only a very small lump when it points away.

It's important to ignore the very narrowband spikes in the spectrum. These narrowband spikes are simply radio interference from electronics from neighbors - probably TVs or monitors as we note that most of the interference occurs during the day. There is also a large constant spike which appears to be an artifact of the LNA. The LNA we used has a 1420 MHz filter built in, but LCD TVs and other electronics in today's suburban environment spew noise all across the spectrum, even at 1420 MHz.

You can also note that the hydrogen line peak is moving around in frequency as different parts of the galaxy pass overhead. This indicates the doppler shift of the part of the galaxy being observed. Because the arms of the galaxy and the hydrogen in it is rotating at significant speeds, the frequency is doppler shifted relative to us.

Using the power and doppler shift data of the hydrogen line is how astronomers first determined the properties of our galaxy like shape, size and rotational speed. If we continued to scan the sky over a few months, we could eventually build up a full map of our galaxy, like what CCERA have done as explained in this previous post.

Continue reading →

A FM Radio Passive Radar System from Two RTL-SDR Dongles

Over on his blog, Max Manning has posted about his senior year design project which was an RTL-SDR based passive radar system that he created with his project partner Derek Capone. Max's writeup explains what passive radar is, and how the theory works in a very easy to understand way, utilizing graphs and short animations to help with the understanding. The rest of the post then goes into some deeper math, which is also fully explained.

Passive Radar works by using already existing powerful transmitters such as those for TV/FM. A receiver listens for these signals being reflected off of objects like aircraft and vehicles, and compares the reflection with a signal received directly from the transmitter. From this information a speed/range graph of detected objects can be calculated

For hardware, the team used two RTL-SDR dongles with the local oscillators connected together. A standard dipole is used as the reference antenna, and a 5-element Yagi is used as the surveillance antenna.

Max's post is a great read for those trying to understand how to do passive radar with a KerberosSDR which is our 4x coherent input RTL-SDR unit available from the Othernet store or Hacker warehouse. Being a radio capable of coherency, it is useful for applications like passive radar and direction finding. 

Their code is all open source and available on GitHub. We note that their code should also work with KerberosSDR with only either zero to minor modifications required. However, for the KerberosSDR we also have our own passive radar code available which might be a little easier to setup via the GUI.

Passive Radar with Two RTL-SDR dongles sharing a single clock.
Passive Radar with Two RTL-SDR dongles sharing a single clock.

How to Not Break Your SDR + Other Articles from oneSDR

A new software defined radio blog called onesdr.com has recently posted a useful article for radio world newbies called "How Not to Break your Software-defined Radio Hardware". The article goes over a few important precautions like avoiding input power which is too high from transmitters and LNAs, avoiding DC input, and avoiding ESD.

They've also uploaded a few other articles that may be useful like "What is a Bias Tee?", "FM Notch Filters – why you need one with most SDRs", "What to look for when buying a Software-Defined Radio (SDR)", "Should I place a Low Noise Amplifier Before or After a Filter?", "The Best Software-Defined Radios (SDRs) for 2020" as well as several more.

Hackaday Tutorial: A Crash Course in RF Modulation – ASK, FSK and LoRa Explained Simply

Hackaday writer Danie Conradie has recently posted a new tutorial explaining the difference between some common RF modulation choices. To do this he uses various RF hardware modules, and an RTL-SDR Blog V3 unit to view the spectrum of each modulation type. In the post he compares Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK), and LoRa. He also explains the differences between ASK and OOK modulation, and FSK and GFSK modulation.

The key takeaways are that ASK modulation is simple, but prone to interference. FSK is less prone to interference, but requires more bandwidth. LoRa is good for receiver sensitivity and interference immunity, but comes at the expense of bandwidth efficiency. In addition LoRa modulation is patented, resulting in higher hardware costs.

Comparing the spectrum of a pure FSK signal, versus a Gaussian FSK signal.
Comparing the spectrum of a pure FSK signal, versus a Gaussian FSK signal.

A Hydrogen Line Telescope Made from Cereal Boxes and an RTL-SDR

SpaceAustralia.com have recently been hosting a community science project that involves encouraging teams to build backyard radio telescopes that can detect the arms of our Milky Way Galaxy by receiving the Hydrogen line frequency of 1420 MHz.

This can be achieved at home by building a horn antenna out of cardboard and aluminum foil, and a feed from a tin can. Then the Hydrogen line and galactic plane can be detected by using an RTL-SDR, LNA, and software capable of averaging an FFT spectrum over a long period of time.

While most horn antennas are typically made from four walls, one participant, Vanessa Chapman, has shown that even trash can be used to observe the galaxy. Vanessa's horn antenna is made from multiple cereal boxes lined with aluminum foil and an old tin fuel can. The boxes are held together by some string and propped up by some sticks.

With her cereal box horn antenna combined with an RTL-SDR Blog V3, and an RTL-SDR Blog Wideband LNA, Vanessa was able to use software to average the spectrum over time as the galactic plane passed overhead, revealing the Hydrogen line peak and corresponding doppler shift from the galactic plane.

Vanessa's Hydrogen Line Radio Telescope made from Cereal Boxes
Vanessa's Hydrogen Line Radio Telescope made from Cereal Boxes

If you don't know what the Hydrogen line is, we'll explain it here. Hydrogen atoms randomly emit photons at a wavelength of 21cm (1420.4058 MHz). Normally a single hydrogen atom will only very rarely emit a photon, but space and the galaxy is filled with many hydrogen atoms so the average effect is an observable RF power spike at 1420.4058 MHz. By pointing a radio telescope at the night sky and integrating/averaging the RF power over time, a power spike indicating the hydrogen line can be observed in a frequency spectrum plot. This can be used for some interesting experiments, for example you could measure the size and shape of our galaxy. Thicker areas of the galaxy will have more hydrogen and thus a larger spike, whereas the spike will be significantly smaller when not pointing within the galactic plane. You can also measure the rotational speed of our galaxy by noting the frequency doppler shift.

KerberosSDR 4-Channel RTL-SDR Passive Radar with Peak Hold Display

Recently we've been testing a simple peak hold for the KerberosSDR passive radar display. This results in some nice graphs that show aircraft and vehicle activity over time. 

Passive radar works by using already existing transmitters such as those for HDTV and listening for reflections that bounce off of RF reflective objects. With a two antenna setup, it is possible to generate a bistatic range/doppler speed graph of reflected objects.

With the reference Yagi antenna pointed towards a 600 MHz DVB-T tower, and the surveillance antenna pointed to an airport we were able to obtain the graph below. The top two large traces show aircraft heading towards our station, whereas the bottom traces show aircraft leaving the airport. Also visible are multiple blips with smaller doppler speeds, and these correspond to vehicles.

KerberosSDR Passive Radar Display Peak Hold
KerberosSDR Passive Radar Display Peak Hold

The code on the KerberosSDR git will be updated in a few days time. We are also working on a more comprehensive passive radar tutorial that will try to explain concepts like processing gain, bistatic ranges and other important tips for getting good passive radar results. At the same time we're also working on improving direction finding ease of use by prototyping antenna switches for calibration, and working on getting 4-channel beamformed passive radar working which will allow us to plot passive radar returns on a real map.

The KerberosSDR is our 4-channel phase coherent capable RTL-SDR unit that we previously crowdfunded back in 2018.  With a 4-channel phase coherent RTL-SDR interesting applications like radio direction finding, passive radar and beam forming become possible. It can also be used as 4 separate RTL-SDRs for multichannel monitoring. KerberosSDR is currently available from the Othernet store and Hacker Warehouse for US$149.95.