Tag Archives: SDR

Ohio Section Journal – The Technical Coordinator – January 2021 edition

One of the responsibilities of the Technical Coordinator in the Ohio Section is to submit something for the Section Journal. The Section Journal covers Amateur Radio related things happening in and around the ARRL Ohio Section. It is published by the Section Manager Tom – WB8LCD and articles are submitted by cabinet members.

Once my article is published in the Journal, I will also make it available on my site with a link to the published edition.

You can receive the Journal and other Ohio Section news by joining the mailing list Tom has setup. You do not need to be a member of the ARRL, Ohio Section, or even a ham to join the mailing list. Please sign up!

If you are an ARRL member and reside in the Ohio Section, update your mailing preferences to receive Ohio Section news in your inbox. Those residing outside the section will need to use the mailing list link above.
Updating your ARRL profile will deliver news from the section where you reside (if the leadership chooses to use this method).
Go to www.arrl.org and logon.
Click Edit your Profile.
You will be taken to the Edit Your Profile page. On the first tab Edit Info, verify your Email address is correct.
Click the Edit Email Subscriptions tab.
Check the News and information from your Division Director and Section Manager box.
Click Save.

Now without further ado…

Read the full edition at:

Jeff Kopcak – TC

DSCF5081 K8JTKHey gang,

For some time, the ARRL and myself have recognized the importance of makers as a way to breathe new life into the hobby. In one of my last in person appearances, our State Government Liaison, Bob – W2THU, posed the question to me: ‘how do we get younger people into the hobby?’ Some time ago my answer would have been “digital” but, in recent years, has shifted to makers – not only as a way to get younger people but a way to get like-minded people into the hobby.

What are makers? Adam Savage of MythBusters: “Humans do two things that make us unique from all other animals; we use tools and we tell stories. And when you make something, you’re doing both at once.” There is no single definition. Responses are broad and varied. A broad definition includes someone who creates something, usually in relation to creating, inventing, and learning. Frequently associated with makers are makerspaces, also called hackerspaces or fablabs. These offer shared resources by way of amenities such as machine shop, wood shop, welding shop, electronics lab, 3D printer, laser engraver, art supplies, blacksmithing, molding and casting, robotics lab, CAD software, glass blowing, space for experiments, and even entrepreneurship classes. These are things you might like to have, own, but are too expensive, unreasonable to own, or would be only utilized for a project or two.

Amateur Radio licensing class in a makerspace

A blog post by Rob – KJ7NZL makes very strong arguments why the ham radio community needs to embrace hackers now more than ever. Hackers are usually promoted as something “bad” when it is hackers that figure out how something works and then explore possibilities. Sure, license numbers are on the rise in the hobby but no one is pushing the limits of RF technologies. I’ve always been proud of the fact hams were using receiver voting systems and ways to detect a weakening signal at one receiver while, at the same time, increasing at another receiver. This, well before cell phone carriers built their networks on the same technology. However, instead of hams leading the way, we’re now lagging behind by adopting developed technologies and making them work for our own purposes. Prime examples being DMR, P25, and NXDN. There are no call signs in these radios. Radios identify themselves with a 5- or 7-digit ID. Other issues aside, D-STAR was at least developed by hams and implemented by manufactures.

Rob makes a number of compelling points to attract hackers. “Stop Primarily Promoting Emergency Communications.” I’ve always seen Amateur Radio having two distinct draws to the hobby: emcomm and experimentation. While I agree with his point personally, I’m also pretty biased. Under “Basis and purpose” at the beginning of Part 97 is the following:

The rules and regulations in this part are designed to provide an amateur radio service having a fundamental purpose as expressed in the following principles:

(a) Recognition and enhancement of the value of the amateur service to the public as a voluntary noncommercial communication service, particularly with respect to providing emergency communications.

Bold added to highlight. While promoting is not providing, it’s still the first reason of purpose. There are significant amounts of time and effort by our leadership and everyone involved with aspects of emcomm, including myself, to build and maintain relationships with governmental entities, keep up with regulation, political and policy changes, and training – to name a few. Lessen their efforts is likely throwing the baby out with the bath water. At the same time, I’m not talking about preppers and anyone with a Tech license and a Baofeng who really thinks they’re going to save the world. If the SHTF, I’m going to be more worried about my family and getting my behind to safety. Grabbing an HT might be on the list but it won’t be top of mind.

As Rob points out in his post, the hacker community isn’t going to care about sending messages during thunderstorms. When you mention Amateur Radio to those not in the community, most go to the prepper or underground bunker imagery because that’s what they know ham radio to be. Not those making, creating, and hacking things to improve, not only the hobby but maybe the portable life-chronicling device everyone carries around called a phone. Not promoting this important hacker aspect of the hobby has brought us to where we are today. The technical side is seen as less important.

In the same vein as preppers and Baofeng users, hackers need to be responsible. Your ham license does NOT give you any right to illegally access or manipulate private property without permission or accessing other radio systems over-the-air. Don’t think so? Ask a judge if you have any right to be on the statewide or regional public safety systems as a ham or regular citizen. No, no you absolutely do not.

“Start Promoting Software Defined Radio.” There is a lot of potential in SDR devices and I feel hams aren’t utilizing these devices to their maximum potential. SDR might usher in talent. If we, hams, keep downplaying technologists by saying ‘ooooohhh, it needs a COMPUTER, it’s not ham radio!’ this hobby is already dead. Thanks, thanks a lot.

Luckily, SDR devices are readily available from $20 for an RTL-SDR RTL2832U to thousands for a FlexRadio, and everywhere in-between. You can do a lot with the inexpensive RTL-SDR, much of it using ham modes and bands. I’m happy to say one of the people I’ve learned the most about radio signals is a licensed ham, Mike Ossmann – AE3H of Great Scott Gadgets, the company behind the HackRF One.

Technical regulation, I believe, is also hampering these efforts. Why are we still limited to baud rates of 300 on some bands? Why are we not at the point of reasonable bandwidth requirements? I have no friggin’ idea. Let’s really find out what we can do within 2.8 kHz. Baud rate and the encryption/privacy debate are two topics I think we need to figure out – three weeks ago. Privacy debate includes the self-doxing requirement of having our own personally identifiable information (PII) available to the public. Many people, in particular women, do not want their address available on the Internet.

Antenna building class (castlemakers.org)

“Provide Communities That Foster Technical Discussion and Exploration.” I didn’t realize this was as big of an issue. Likely in reaction to the blog post, I’ve had stations appear on the K8JTK Hub saying they were looking for places to have technical discussions. A younger ham stated something to the effect, ‘I’m looking for places that have technical discussions. I’m not looking to make a quick QSO and talk about the weather.’ I could think of a couple technical nets but not dedicated reflectors or talkgroups for in-depth technical discussions. I informed him that while my system is open, there wasn’t only technical discussions taking place but he was welcome to use it if he encountered or wanted to hold such discussion. Then we had an hour long (or more) QSO on everything from cryptocurrency to Internet routers and Wi-Fi access points. It’s not going to be for everyone but it was nice to have in-depth technical discussions.

Rob created a YSFReflector to facilitate technical discussion: #33360 – Radio Hackers. Dashboard: http://hackers.ysf.kj7nzl.net. Immediately saw comments ‘ooohhh, it’s using YAESU radios and WIRES-X.’ I love it. Not really. Everyone conflates the YSF/YSFReflector system, which is an open source Fusion reflector system, with WIRES-X, which is closed-source and proprietary to Yaesu and Yaesu equipment. Yaesu System Fusion as a standard, the technology in the radio and repeaters, is also closed-sourced. YSFReflectors are easy to setup and likely the reason Rob went there first.

Hackerspaces are excellent communities to promote the technical nature of ham radio. If your club is not involved with a hacker or makerspace, support a club that is involved. Or start talking with one near you. You’ll probably find they are waiting for a club or someone to partner with on radio, circuits, or electronics.

What are you doing to promote the technical side of the hobby?

Thanks for reading and 73… de Jeff – K8JTK

Ohio Section Journal – The Technical Coordinator – July 2019 edition

One of the responsibilities of the Technical Coordinator in the Ohio Section is to submit something for the Section Journal. The Section Journal covers Amateur Radio related things happening in and around the ARRL Ohio Section. It is published by the Section Manager Scott – N8SY and articles are submitted by cabinet members.

Once my article is published in the Journal, I will also make it available on my site with a link to the published edition.

You can receive the Journal and other Ohio Section news by joining the mailing list Scott has setup. You do not need to be a member of the ARRL, Ohio Section, or even a ham to join the mailing list. Please sign up!

If you are an ARRL member and reside in the Ohio Section, update your mailing preferences to receive Ohio Section news in your inbox. Those residing outside the section will need to use the mailing list link above.
Updating your ARRL profile will deliver news from the section where you reside (if the leadership chooses to use this method).
Go to www.arrl.org and logon.
Click Edit your Profile.
You will be taken to the Edit Your Profile page. On the first tab Edit Info, verify your Email address is correct.
Click the Edit Email Subscriptions tab.
Check the News and information from your Division Director and Section Manager box.
Click Save.

Now without further ado…

Read the full edition at:

Jeff Kopcak – TC

DSCF5081 K8JTKHey gang,

The latest addition to the Pi family is here – Raspberry Pi 4. Boasting impressive upgrades, this latest version of the device is becoming a suitable replacement desktop PC or multimedia device. Pi 4 keeps the same form factor and still remains competitive at the $35 starting price.
Device highlights:

  • 64-bit quad core processor running at 1.5 GHz with built-in metal heatsink
  • 1 GB, 2 GB, or 4 GB RAM configurations
  • 2 USB 3.0 ports
  • 2 USB 2.0 ports
  • Gigabit Ethernet with Power over Ethernet (requires separate PoE HAT)
  • 2.4 and 5 GHz Wireless LAN
  • 2x micro-HDMI ports supporting 2 – 4K monitors
  • Micro-SD card slot for operating system and storage
  • 5V DC USB-C power connector
  • Standard Pi 40-pin GPIO with 5V DC

Instead of a single memory configuration, a new tiered pricing structure was introduced for the three different RAM configurations:

  • 1 GB: $35
  • 2 GB: $45
  • 4 GB: $55

Even the 4 GB model is very reasonable at $55. The addition of USB 3.0 and Gigabit Ethernet allows for faster network and data transfers. Great for rolling your own network storage or video streaming server.

The form factor remains the same but due to changes in the power and video connectors, existing Pi cases will not fit. The power connector changes from a micro-USB to a USB-C connector. Probably in an effort to alleviate the most common problem using the Pi, finding a quality power supply, the Raspberry Pi Foundation is selling an official USB-C 15W power supply. Micro-HDMI cables or adapters are required to connect a TV or video display.

Noobs/Raspbian remains the official operating system and comes with a push to the next version from Raspbian Stretch to Raspbian Buster. Existing Pi installations can benefit from a hardware upgrade even using the same SD card in a new Pi 4. MAKE SURE you have updated the Raspbian operating system to take advantage of the new chipsets. Existing installations WILL NOT work without an operating system upgrade. Availability in other Raspberry Pi projects not based on the official Raspbian operating system will depend on the project. A Linux Kernel update will likely be required and may come via package manager, manual update, automatic update, or at worst, a re-image of the SD card. Remember to backup first! The HamVoIP AllStar project I wrote about a couple months ago stated a Kernel update is required for Arch Linux and will come via their automated update menu option.

When is the new hotness available? Well, now. Sort of. The Raspberry Pi 4 was released June 28, 2019 but you’re going to have a hard time finding them in stock. The Pi Foundation has a list of official vendors. Checking Newark Element 14, Micro-center, and my favorite place to buy Pi and quality components, Adafruit, were all out of stock. Estimates were 2-3 months before more would be available. Check out this substantial update to this credit card-sized computing device for your next project.


HF bands dead lately? Not if you are an FT8 user. This mode has kept the bands active with the lack of solar activity. Unless it’s a contest weekend, I’m seeing little CW activity and less voice. There’s that 3 kHz of FT8 where there is always activity. I think FT8 keeps hams excited about ham radio and operating in general during an otherwise miserable sunspot cycle.

FT8 allows a complete exchange in 1:30, from CQ to 73. High power and high-profile antennas are not a requirement. Low power and “apartment” type antennas work well too. At times, I don’t see any trace on the waterfall of the station I’m working.

The program and protocol are open-source allowing others to build other applications using the protocol. Those include JS8Call which takes the robustness of FT8 and builds a messaging protocol with the ability to relay messages, similar to FSQ.

The good keep getting faster, better, cheaper. On July 16th, version 2.1.0 of WSJT-X was released for general availability and introduced a new mode, FT4. According to Dr. Taylor – K1JT, developer of the WSJT protocols, message types are the same as FT8. Improvements over FT8 include a mode that acts more like RTTY, meaning no more fighting to keep your computer clock synced with UTC and no designated transmit times. Transmission duration is 4.48s vs 12.64s of FT8. Bandwidth is 90 Hz. A compromise for quickness is the ability to dig out weak signals. FT8 is limited to around -21dB, FT4 is about -16dB. For reference, an excellent CW operator who can pull out weak signals is -15dB (figures from the video). Update now to start experimenting with the new exciting addition to the WSJT family!


A service for collaboration I’ve been using lately is Groups.io. Joined during my recent trip to D.C. because a mesh group was using it for collaboration. I quickly noticed other ham projects I was interested in were using it too, like the East Coast Reflector and NW Digital Radio. It’s a service similar to Yahoo and Google Groups but so much better. Groups.io doesn’t serve ads, track users, and has a better reputation than Facebook, which I neither use nor trust. Featuring a modern platform for communities to connect through messaging, calendar, chat, polls, database, photos, wiki, and integration with a list of other platforms. Great for projects to post documentation and offer support or a platform to keep in-touch with club members. It will even move your Yahoo or Google Group over to Groups.io. It’s a freemium service. Most will find the free offering more than adequate. The $10/month level adds the ability to directly manage memberships and take donations.

IC-7300 Clock Sync Video

Have an ICOM IC-7300? Want to keep the radio’s clock in sync with a PC while learning Linux and Python programming in the process? Check out the tutorial video by Kevin – KB9RLW, the “old tech guy.” He talks about why he wants to keep the clock synced and explains the program he wrote. His script is heavily commented which helps to understand the commands and he explains each part in the video. The script is available on GitHub which means it’s easily to build upon. I really like Python and started to use it when I was still doing programming. Alot of Linux programs are written using Python meaning it has to be a powerful language. Depending which survey, it’s #1 or in the top 3 most popular programming languages used today.

SDR Concepts

Onno – VK6FLAB produces a podcast called Foundations of Amateur Radio. Unlike others, each episode averages 5 minutes. They are short, very concise, and does an excellent job of explaining topics efficiently. Since April, episodes have been focused on Software Defined Radios (SDR). A must listen if you picked up an SDR-based radio at Dayton this year and want to learn more. Covering terminology like Direct Conversion and Sample Rate, even comparing SDR to ones with transistors or valves.

Apollo 11 50th Anniversary

When this article goes to press, we’re in the middle of the Apollo 11 mission 50th anniversary first landing on the moon. I’m already out there working those on the air special event stations. Many are operating until July 24, only have a couple more days! Check the Special Event Station listing or the DX Spotting networks.

Steve – W8HF sent me a website that is amazingly cool beyond words. When someone asks to define sites that make the Internet, this should rank near the top. Called Apollo 11 in Real-time, it is “a real-time journey through the first landing on the Moon” and is “entirely of original historical mission material.” When you visit the site, you can select to visit the launch 1-minute prior or visit the mission in real-time, 50 years ago. Included in the real-time elements are mission control footage, TV transmissions, 2,000 photographs, 11,000 hours of Mission Control audio and discussions, 240 hours of space-to-ground audio. All synced and organized chronologically. Truly an awesome website and I hope they keep it online for a long time.

Thanks for reading and 73… de Jeff – K8JTK

Dongle Bits: ADSB Radar and $60 Police Scanner

This article appeared in the The Lake Erie Amateur Radio Association newsletter The Spirit of ’76 and ’88 February 2015 edition and The Wood County Amateur Radio Club newsletter CQ Chatter March 2015 edition.

Read the rest of the series in the Dongle Bits articles category.

The holidays were a busy time at the K8JTK laboratories with a couple RTL-SDR projects. The RTL-SDR is the European TV tuner dongle that was turned into a software defined radio receiver.

Thanksgiving is one of the busiest travel seasons and I wanted to decode ADS-B data to see how many aircraft were flying around. ADS-B stands for Automatic Dependent Surveillance – Broadcast allowing aircraft to be tracked by ground stations and provide situational awareness to nearby aircraft. This is part of the FAA’s NextGen project and mandated by agencies across the globe.

I saw this project in the January 2014 edition of QST written by Robert – W9RAN. He covered building a Collinear Array for the ADS-B frequency of 1090 MHz. I used one of my ham antennas. The RF signal received by the dongle is turned into data packets by a program called ADSB# (included in the SDR# download). VirtualRadar receives those packets, decodes the data, and plots aircraft on Google Maps. This setup can work with a Raspberry Pi and I hope to try this in the future.

Thanksgiving travel in Cleveland, Ohio.

Over the Thanksgiving holiday, I saw 25 aircraft flying around Cleveland on average. I think the most I saw was 48 at once. Not all aircraft have full ADS-B implementations. For example: I would see a call sign but no position data. My receive range (depending on aircraft altitude) was east of Toledo to the PA border and south to Canton. Visit my write-up on this project: ADS-B Decoding with ADSBSharp and VirtualRadar Server.

The second project is a little more complicated but it helped me understand how trunked radio systems work. With the FCC narrowbanding mandate in certain RF spectrum, many public service agencies have decided to “go digital.” In my area the MARCS-IP system and the Greater Cleveland Radio Communications Network are most popular. Both are P25 trunked digital systems. P25 is a specification for voice and data transmission. Trunked radio systems operate by having a radio send data to the control channel requesting communication on a talkgroup. The control channel directs all users of that talkgroup to a specified channel. When the user is done transmitting, all radios switch back to monitoring the control channel for further instructions. This is done seamlessly and allows many users (agencies) to use a small set of radio frequencies. Users only hear the conversations on their assigned talkgroup and not other users on the same system.

P25 trunked decoding with a single voice decoder.

Scanners that receive these systems run $500 and go up from there. Using two RTL-SDR dongles and software (mostly free), I’ve been able to receive P25 trunked systems for about $65. One dongle monitors only the control channel and other dongle(s) jump frequencies to receive the digital voice modulation with a program decoding the audio. I can have as many voice receivers as I want whereas a scanner cannot be expanded. Most I’ve heard of is eight. There are some drawbacks like portability. Find out my experiences in my P25 Trunked Tracking post.

Fresh Baked Pi

Raspberry Pi foundation released new models over the last couple months. The biggest news coming at the beginning of February: the Raspberry Pi 2. This model comes with a quad-core CPU and 1GB RAM offering a six times speed improvement, still at $35. Initial reports are it is a lot faster!

Raspberry Pi 2

Along with the new Pi2 came a new version of the Raspbian operating system with optimizations and a new look. In the near future, Microsoft will be releasing a version of Windows 10 Embedded for the Raspberry Pi 2 FREE OF CHARGE! (see the Raspberry Pi 2 link above.)

That’s A Wrap

A goal behind this series has been to expose many hams to newer technologies and younger people to ham radio. These technologies are getting young people interested in experimenting, programming, and even Ham Radio. On podcasts I watch, I’ve heard “I want to get my Ham Radio license” by 20 and 30 year olds like I’ve never heard before. These are young people interested in experimenting, making things, building things, and hacking things — all of which are the foundation of Amateur Radio. Making has evolved into writing software, sending a chip a set of commands and analyzing what is returned, or analyzing packets. Then figuring out “what can I do with this?”

I saw a great technology round-table over the holidays and they talked about getting kids into technology. Many of the methods apply to Ham Radio. As a builder, you build something and presume what will happen. Then something different happens and now you have a mystery to solve. “Why did X happen and not Y?” A new theory develops and sucks you in. This is exactly how the Raspberry Pi, RTL-SDR, and every project surrounding them came to be. It is my opinion that we, as the Amateur Radio community, need to encourage, capitalize, and focus efforts on younger makers and hackers to get them licensed.

As this is my last planned article, I would like to take time and thank the newsletter editors for thinking this series was worth publishing and recreating all the links I included. Thank you to those who told others about this series. I got a ton of feedback and couldn’t be happier that others have found this interesting and sparked them to start experimenting. Most of all, thank you for reading.

P25 Trunked Tracking and Decoding with RTL-SDR, Unitrunker, and DSDPlus

The project that got me really into experimenting with the RTL-SDR dongles is using them to decode P25 digital trunked public service radio systems.  I have been a casual scanner listener for years and like to listen to emergency calls nearby.  In college it was great to listen in on a party weekend hearing fights, disturbances, or why my street suddenly filled with cars at 3 AM.


That was when most agencies were analog.  To get more use out of the radio spectrum, the FCC decreed a narrowbanding mandate requiring a “maximum of 12.5 kHz bandwidth across the private land mobile bands between 150-174 and 421-512 MHz.”  This means going digital for much of that radio spectrum because traditional FM transmissions are 15 KHz.  Ironically they will “go digital” but move to 700/800 MHz.

As a casual listener, I wasn’t exactly thrilled with spending at least $500 for a scanner capable of digital (P25 mostly) and trunked system tracking (also Radio Reference wiki).

$40 RTL-SDR trunked scanner

Lurking around the Radio Reference forums, I saw references to being able to use the RTL-SDR dongles for trunked digital decoding.  I had to try it.  I had played around with these dongles and read about the many projects people were doing with them.  In actuality this project cost me $65.

About the project

You will need at least two RTL-SDR dongles ($20/each) and a copy of Virtual Audio Cable ($26).  I already had a premium Radio Reference account.  You can do the project with one dongle but you loose many features in Unitrunker like talkgroup priority.  Theoretically, the single dongle listens to the system control channel and then tunes to voice calls, then back to the control channel.  You will miss calls because that notification comes across the control channel while the dongle was tuned to a voice transmission.  I will cover a two dongle setup and do not plan to cover a single dongle setup.

This project is still very complicated but it is MUCH easier than it used to be.  This manly thanks to Rick, the developer of Unitrunker who implemented support for the RTL-SDR chipset in his program.  Previously, there needed to be a plug-in for both Unitrunker and SDRSharp, there were all kinds of “moving parts.”  In one respect, being able to see the signal waveform on a spectrum analyzer made it much easier to fine tune the PPM correction on-the-fly as opposed to guessing on a modulation scope.  This setup is much cleaner and the Unitrunker developer has implemented advanced features like drift correction.  It will take some time and patience to understand, research, and know the types of systems and system specifics.

There are some advantages like cost and being software based.  Changing modulation types is often as easy as changing programs.  As an example, DSDPlus will decode MotoTrbo as opposed to no standalone scanner being able to do so currently.  However, portability of this setup is limited as you have to have many pieces of equipment with you.  You’ll need an Internet connection to find sites to program and a PC to tweak settings.

Two very specific and key things to note about trunked radio systems in general:

  • You cannot tell the tower your’re listening to which talkgroup you want to monitor.  Doing so would require the ability to transmit and IS ILLEGAL because you are not authorized to do so.  If the talkgroup is not transmitted by the tower, you’re out of luck.  You can’t be in Dayton and tell the system you want to listen to a talkgroup originating from Cleveland.
  • Nothing here (and no program I know of) will defeat encryption, even if you own the keys.  Decoding encrypted transmissions is not implemented in any of these programs.  On the flip side, be aware that using this tutorial and feeding the audio to Radio Reference and Broadcastify may not make agencies happy.  You could get a take-down notice or even worse, it is trivial to turn on encryption at the system level and you just blocked reception for all scanner listeners.

Thanks to those whose tutorials I first used getting this setup working: $20 trunking police scanner and RTL-SDR Tutorial: Following Trunked Radio With Unitrunker.

Program versions

I used a Windows 7 64 bit PC. Applications and versions used in this writeup:

  • SDRSharp:
  • Virtual Audio Cable: 4.14
  • DSDPlus: 1.51
  • UniTrunker:

Parts list

Listed below are all the parts needed to get this project working.

  • Computer with some processing and memory horse power.  It is recommended to have a computer with a recent Intel Core i5 processor and 8GB of RAM, or better.
  • Receive antenna that covers 700 & 800 MHz where P25 trunked usually resides. For an external antenna, splitters and coax runs maybe needed.  The stock RTL-SDR dongle antennas worked fine for me.
  • Two RTL-SDR Dongles.  To decode more than one voice transmission, increase the number of dongles needed.
  • Virtual Audio Cable.  Not free but trial version available.
  • Radio Reference account.  Premium account.  If you don’t want to fork over the money, become an audio feed provider.
  • Recommend a USB hub.  Couple years ago I picked up a Rosewill RHUB-300 USB 2.0 Hub 7-Port HUB.  I recommend this hub because when the dongle is plugged in, the antenna connector is pointed up.  This makes it easier to connect an adapter and a Pryme RD-98.  If available, connect the hub to an Intel USB chipset on your motherboard.  I’ve had far less issues using Intel based hardware.

ADS-B Decoding with RTL-SDR, ADSBSharp, and Virtual Radar Server

Update: ADSBSharp (ADSB#) is no longer available and has been deprecated.  Copies can be found by doing some searching.  It is not available from the authors site as described in this post for the RTL-SDR. A program like RTL1090 or Dump1090 (or any of its forks) can be substituted.  The author is focusing on AirSpy devices and ADSBSpy is available from the same site as SDR#.

An interesting project I came across using the RTL-SDR dongle is to decode ADS-B data.  ADS-B stands for Automatic dependent surveillance – broadcast allowing aircraft to be tracked by ground stations and provide situational awareness to nearby aircraft.  It is part of the FAA’s NextGen project and mandated by agencies across the globe.  ADS-B uses a frequency of 1090 MHz.

Thanks goes out to Robert Nickels – W9RAN and his article in the January 2014 edition of QST which covers this project and how to make a Collinear Array for 1090.  HAK5 also did a couple episodes showing how to make an antenna and configure Virtual Radar Server.

Block diagram of the ADS-B Hub setup. From: QST, January 2014.

Program versions

I used a Windows 7 64 bit PC.  Applications and versions used in this writeup…

Virtual Radar Server: 2.0.2
SBS Resources: 6.7

Parts list

Listed below are all the parts needed to get this project working.

Antenna with receive coverage of 1090 MHz.
RTL-SDR dongle.

I had a ham radio antenna that I used.  It is the MP Antenna 08-ANT-0860 Ultra Mobile Antenna if you’re interested.  To build an antenna, see the QST article above.  The one that comes with the dongle will work but at short range.

Dongle Bits: Settings, Programs, & Apps for Software Defined Radio

This article appeared in the The Lake Erie Amateur Radio Association newsletter The Spirit of ’76 and ’88 October 2014 edition and The Wood County Amateur Radio Club newsletter CQ Chatter November 2014 edition.

Read the rest of the series in the Dongle Bits articles category.

Last time on Dongle Bits, I talked about the $20 European TV tuner dongle that was hacked allowing direct access to the signal data. The result is a cheap wideband receiver for your computer. We’re going to take a look at key settings you should know about when using these devices. Then look at some software and projects that transform these into systems that would have cost hundreds or thousands of dollars!

PPM and Settings

An important thing to know about these dongles: they are cheaply made and not tested for accuracy. They are designed to receive DVB-T signals at a bandwidth of 6 – 8 MHz where a few KHz error doesn’t matter. This is obviously not true when you’re dealing with FM signals that are 16 KHz wide or digital at 12.5 where a few KHz will put you on a completely different frequency or channel.

PPM stands for parts per million and is the difference in received frequency vs. frequency shown. To visualize this, use SDRSharp to receive a known FM signal. The center frequency shown will be different from the signal on the scope. Typical PPM offset is anywhere from 45 – 65 and will be in the programs settings. The dongle will drift another 2 – 5 PPM over the next 20 – 45 minutes as it warms up. Gain is obviously another setting that will help you receive signals. The RTL AGC setting works but will err on the side of too much gain. Manually, using more than 32.8 dB will overload and produce duplicate signal spikes. The Correct IQ setting will get rid of phantom spikes at lower gain settings.

PPM at 0
Dongle with no frequency correction. The actual 162.550 frequency is just to the left of the displayed frequency. 162.550 is one of the NOAA Weather Radio frequencies.
RTL-SDR Settings (PPM corrected)
Shows the gain and PPM frequency correction of 55 for the dongle I’m using.
PPM Corrected
Shows 162.550 centered with frequency correction applied.

The crystals on the RTL-SDR dongle can be replaced with higher accuracy temperature controlled crystals (TCXO) that have a variance of 1 ppm! These crystals are $10 but you have to wait for them to ship from China. Pre-modified dongles are available but you will pay three times the price for the dongle.


PCs aren’t the only place these SDRs can be used. They can be plugged into an Android device too. You will need a USB OTG cable (on-the-go) and Android 3.1 or later. Search Amazon or EBay for “USB OTG.” OTG is a standard for plugging in USB keyboards, mice, and thumb drives into mobile devices. Running external USB devices off the internal battery will drain it much faster. A powered USB hub would off-load the dongle power consumption. Apps include SDR Touch (wideband receiver program), ADSB Receiver, and SDRWeather for monitoring NOAA weather alerts on your device.

This is the RTL-SDR running on my Android Nexus 7 tablet with SDR Touch receiving the 146.880 repeater in Lakewood, Ohio. It is connected with a USB OTG cable to the RTL-SDR dongle, then to an MCX to SMA, and then SMA to PL259 adapter.
This is a screenshot of the above setup with SDR Touch.

What can I do with this thing?

The definitive source on all things RTL-SDR is at the appropriately named www.rtl-sdr.com website. This site has it all. They regularly post software, updates, projects, and new developments. There is something new just about every week.

Some features of RTL-STR.com are The Big List Of RTL-SDR Supported Software. This is the list of software packages that support RTL-SDR on all platforms. Software ranges from wideband receivers to single purpose programs. This will give you some ideas of things to try with RTL-SDR. SDRSharp was written to have plugins extend the functionality of the program. These include plugins that make SDRSharp scan frequencies, add an audio FFT, scope, level meter, or CTCSS (PL) detector.

There is an extensive list of projects and write-ups including an Amateur Radio category. Some interesting ones are receiving live NOAA satellite imagery, analyze cellular phone GSM signals, radio astronomy, signal strength heat mapping (foxhunting?), and how Brazil uses our military satellites to transmit SSTV images.

With the onset of many digital standards and narrowbanding, there are more digital signals out there you may not be able to identify by hearing them or seeing them on the waterfall. This Signal Identification Guide has known types, frequencies they may be heard on, mode, bandwidth, sample audio, and waterfall image. I find myself using the Radio Reference database search utilities to help identify signals and their owners (a premium account maybe needed for some features).

My first SDR project was to use the Raspberry Pi as a SDR remote network server. The Raspberry Pi could be placed in an attic or basement connected to an antenna and controlled by another computer.

Audio can be piped from one program into another using Virtual Audio Cable (VAC). Some time ago, during one of the digital nets on the .76 repeater in Cleveland, I used SDRSharp and VAC to receive the FLDIGI messages being passed on the net. The signal path looked like this: received RF signal (146.760) -> RTL-SDR (signal data) -> SDRSharp (audio out) -> Virtual Audio Cable -> FLDIGI (audio in) -> message decoded on screen. If I had a HackRF, I probably would have been able to transmit messages without using any “ham” gear.

The next and probably final article, I will demonstrate tracking airplanes equipped with ADS-B transmitters and listening to trunked P25 public service radio systems for under $100.

Dongle Bits: RPi B+ and $20 SDR

This article appeared in the The Lake Erie Amateur Radio Association newsletter The Spirit of ’76 and ’88 August 2014 edition and The Wood County Amateur Radio Club newsletter CQ Chatter September 2014 edition.

Read the rest of the series in the Dongle Bits articles category.

Before we begin talking about the RTL-SDR dongle as promised, some big news broke. The Raspberry Pi Foundation released the Raspberry Pi Model B+. They point out this is not a “Raspberry Pi 2” but an evolution of the model B board. Price is the same at $35. Key improvements are:

  • More GPIO: 40 pins with the first 26 pins the same as the Model B.
  • More USB: 4 USB 2.0 ports with better hotswap and overcurrent behavior.
  • Micro SD: SD card socket has been replaced with a micro SD version.
  • Lower power consumption: Reduced power consumption by 0.5W to 1W.
  • Better audio: The audio circuit incorporates a dedicated low-noise power supply.
  • Neater form factor: Aligned the USB connectors with the board edge, moved composite video onto the 3.5mm jack, and added four squarely-placed mounting holes.
Raspberry Pi Model B+

For more details, diagrams, and videos, please visit Introducing Raspberry Pi Model B+. Because of the new configuration layout many accessories for the B board will not work with the B+ board.

Now, RTL-SDRs: RTL-SDR is a term used describe a very cheap software defined radio. Other names for this device are: RTL2832U, DVB-T SDR, or “$20 Software Defined Radio.” RTL refers to Realtek Semiconductor Corp most widely known for their computer IC network controllers, card readers, and very popular High Definition Audio codec used in many laptop and desktop computers.

SDR refers to “software defined radio.” Typically radio components like mixers, filters, amplifiers, modulators/demodulators, and detectors are implemented in hardware level components. In SDRs these components are implemented by way of software running on a PC or embedded system. The most widely known SDR in ham radio is FlexRadio.

RTL-SDR Dongle

The RTL-SDR is a DVB-T TV tuner dongle based on the RTL2832U chipset. DVB-T stands for Digital Video Broadcasting – Terrestrial used in the eastern hemisphere (Europe, Asia, Africa, and Australia) as their over-the-air broadcast standard. In contrast, North America uses ATSC (Advanced Television Systems Committee) standard for digital television transmission over-the-air, cable, and satellite networks (sources: DVB-T and ATSC).

Antti Palosaari, Eric Fry, and Osmocom were hackers playing around with these receivers and found the signal data could be accessed directly. This allowed a cheap DVB-T TV tuner to be converted into a wideband software defined radio via a new software driver and used as a computer based radio scanner. Add in software packages to expand the capability and you have a system that would cost hundreds or even thousands of dollars.

RTL-SDR Internal Hardware

The current popular dongle is the NooElec NESDR Mini SDR & DVB-T USB Stick (R820T). It comes with an antenna that only works well for very strong signals. Yes, it does come with a Remote but you don’t need it for SDR. They guarantee the NESDR will have an electrostatic discharge diode (ESD) in their dongles. This is useful when handling the dongle or traveling where the possibility of frying it is greater. However, as I found out, if you drop one of them upon returning from Dayton you’re better off getting another because it just won’t work the same!

Let’s dive into some specifics:

  • RTL2832U Chipset close-up

    Frequency range: depends on the device and chipsets used. The NooElec NESDR has a receive range of 24 – 1766 MHz. The previous Elonics E4000 hotness covered 52 – 2200 MHz. However, that company went out of business making the dongle rare and more expensive.

  • Sample rate: maximum theoretical sample rate is 3.2 MS/s (mega samples per second). The optimal sample rate (without any dropped samples) is 2.4 MS/s.
  • Analog-to-digital conversion resolution: 8 bits.
  • Input impedance: 75 Ohms. The mismatch loss when using 50 Ohm cabling is minimal.
  • Connector type: most use an MCX connector. The E4000 uses a
    MCX Connector

    PAL connector.

These $20 dongles only receive. Other dongles offer better performance but come at a higher price. The FunCube Dongle is an example of this. HackRF (10 – 6000 MHz) and BladeRF (300 – 3800 MHz) are SDR radios that will transmit over their given frequency range. That’s right, wideband transmit! These are even more expensive at $300 – $650 (sources: About RTL-SDR and Buy RTL-SDR Dongles).

What about HF? The dongles themselves don’t cover HF. There are two options for reception: use an upconverter to receive the frequency and convert it up to a frequency the RTL-SDR dongle can receive. Make a hardware modification to allow “direct sampling mode.” HF upconverters are anywhere from $50 – $100 (cheaper if you build your own) and offer better performance over the hardware mod. KF7LZE has a round-up of HF upconverters.

This quickstart guide shows how easy it is to setup and start receiving signals. Windows users will probably start out with SDRsharp (also written SDR#) to receive signals. Linux users have a couple options; GNURadio being the best though it is unwieldy because you build out the SDR from scratch.

These make it easy to receive FM broadcast (WFM), NOAA weather radio, amateur radio, or public service frequencies that are still analog. I will show uses and applications of these SDR receivers including a reason you might want to get two (or more) dongles. Hint: it’s not to replace one after Dayton!