SigPi 5.0: What is it and what does it do?

 

HVDN is happy to announce the release of SigPi 5.0, after lots of hard work by Joe Cupano NE2Z as the chief architect and Steve Bossert K2GOG as laboratory hamster.

SIGpi 5.0 is the root software of a much larger project which is focused on field based signal intelligence gathering and transmission toolset. 

The need for SIGpi comes from a lack of easy to upgrade and easy to use software defined radio applications that is not dependent on ready made images being up to date with current software versions.

SIGpi is not targeted at amateur radio enthusiasts, but any hobbyist (or professional) involved in RF spectrum related interests.

For secure environments built on a stock linux image such as Ubuntu 20.04 or Raspberry OS, the approach of the SIGpi based script based menu driven installation decreases frustration by the end user.

Yes, lets begin! 

As illustrated in pre release 5.0 and older versions, just navigate through the menus to install what you want. 

Newly added into SIGpi is support for the Ettus USRP lab grade SDR platform and also support for the LoRa bonnet which is the original cornerstone of the HASviolet project.

Right away we are showing why SIGpi is different because to explore the RF around you, it is important to support hardware tools with unique capabilities that also allow you to interact with those signals. More about this later.....

General and Extra SDR Applications

Six programs were chosen for basic utility, general and extra value added benefit as the core applications. You can install all, some or none of them but all were chosen for a purpose.

As you can see below, running RTL_433 can expose many signals around you, such as weather station transmitters or the tire pressure monitoring systems (TPMS) found on every car made after 2007.

The inexpensive RTL-SDR V3 when connected will automatically connect and start streaming data as shown, in this case every time a car passes by the SIGpi.

Also connected to the Raspberry Pi 4 is a HackRF which is shown using SDRangel to visualize the 315 MHz spectrum the TPMS sensors are using.

Being able to support multiple SDR devices for different or related tasks is important for signal gathering work.

If there is interest in connecting multiple RTL-SDR V3 or other related USB SDR units, you will need to serialize them so they are all treated as unique devices by the Raspberry Pi. More about RTL_EEPROM can be found here.

Another use case could be watching ADS-B traffic as it flows in as pure data via one RTL-SDR V3 at 1090 MHz and monitor multiple VHF AIR audio channels at the same time along with spectrum scope.

There are many command line based tools that can do similar things which are included in SIGpi such as rtl_adsb, dump1090, rtl_fm and many many more.  Simply, we want to show the core visual applications here first though.

Use Cases for SIGpi

It will be hard to define every use case possible via all the included software with SIGpi, but the benefits are that it is something modular and easy to expand to include new software at any time.

The SIGpi approach also offers the guarantee that the latest version of all included software is installed the first time you install SIGpi.

When you wish to upgrade SIGpi,  you can do this via just one application at a time or all of them.

Here are some select use cases to inspire imagination for SIGpi to be part of your signal intelligence efforts.

Receive Only Use Case Examples

• Explore analog or digital audio communications.

• Use more than one SDR tuned to 3rd harmonics of one signal to assist with direction finding.

• Analyze digital on off key (OOK) and many other signals to determine characteristics.

• Perform situational awareness of  airplanes and boats which transmit GPS data.

• Provide ethical use cases for multi-signal observations.

•  Receive non encrypted video based signals of analog or digital formats.

• Track and monitor high altitude objects such as balloons, rockets and satellites.

• Evaluate all forms of license free communications dependent on your hardware.

Transmit Only Use Case Examples

• Create different non-location based beacon transmitters for different test scenarios.

• Broadcast low power informational material for special events.

• Experiment with location based positioning with or without GPS.

 Combined Transmit/Receive Use Case Examples

• Experiment with re-broadcast capability of radio to radio or internet to radio signals.

• Share bidirectional  internet to radio based signals to fill in short range communications gaps.

• Provide training for "man in middle" type of threat vectors or ethical honey pot deployments.

• Create software defined transcievers for amateur radio via hardware like Lime SDR, RadioBerry, HackRF, QDX, etc

Summary & Support

The community of developers of all the included software makes SIGpi possible.  The HASviolet and Kismet programs are made right here in the Hudson Valley, so please consider supporting them if you live locally which also helps SIGpi grow.  All other programs we encourage the same appreciation.

The scripting and architecture behind SIGpi is well documented and commented on if you wish to explore how things are being connected by looking at SIGpi Git repository or by simply using your favorite text editor after you have installed SIGpi

Who SIGpi is NOT targeted to

The developers of SIGpi encourage ethical use of SIGpi and its suite of community software. 

We do not encourage malicious use of any of the included programs nor will we be providing assistance in implementing non-ethical use of any of the programs which can be used with appropriate hardware to do interesting things.

Thank you to our growing SIGpi community

We hope you enjoy the convenience of SIGpi.  Please join our growing list of stargazers for  SIGpi on Git to show your support.

How do I get my DMR recordings?

 

Kraken is coming and we all need to prepare for its arrival.  On Tuesday October 19th 2021, Steve K2GOG was invited to the North Star Digital Net to give a quick chat about what does it do and why its important for the future within the broader topic of "software defined radio".

A few people who could not attend the live discussion had asked Jim WA2UMP and Steve K2GOG to see if they could record the audio presentation.   This is a fun problem that needed to be solved first to start this article, so read onward!

How do you record DMR audio?

Steve K2GOG planned to use his Alinco DJ-MD5XTG to talk via his hotspot which reaches the Brandmeister 31630 (STEM) talk group.  A nice feature with this radio, as well as the popular Anytone AT-878 series of radio, is that it can record transmit and receive audio with timestamps and by who was speaking.

Its easy to scroll through recorded audio files one by one or play all your recordings on a loop to play them all in order. This could be helpful if you thought you may have missed some important scheduled discussion or activity on your favorite talk group.

One annoyance is that the recordings save to internal memory on the radio instead of a micro SD card, like on radios such as the D-Star focused Kenwood TH-D74 or the Fusion based Yaesu FT-5DR. 

Both of those radios and even the Icom IC-705, all require the user to remove the SD card from the radio to access recorded audio but that makes it really easy to access those files  on your computer and send them to someone to share interesting transmissions like during a satellite contact. 

In the case with the Alinco and Anytone, you need to connect up a cable to your computer to access the recordings but you can not pull those files off which is super annoying. The manufacturers software seems to lock this function out but would otherwise clearly support this as pictured below.

If you click any of the files listed in photo above, the recording simply plays through the radio speaker but we are no closer to sharing the recordings.

The Alinco DJ-MD5 series of radio uses a simple USB micro cable to program the radio but does not output audio.  The way to solve this problem is to use the headphone port on the Alinco which uses the standard 3.5mm plug found on most all consumer headphones.

Using a 3.5mm stereo to stereo cable, the other end plugs right into the microphone jack on your computer sound card.  If you have a modern laptop which uses a TRRS (Tip, Ring1, Ring2, Sleeve) style connector, you may instead need to use a USB sound card as mentioned in Steve's explanation video below.

Now that we have that problem solved, you can use a program like Audacity with the sound activated record function enabled to "re-record" the audio from the radio to your computer.  While this takes a little while to do, it lets you easily stitch together the audio segments you want with no gaps. 

If you are over a certain age where you may remember double cassette recorders, this activity may bring back memories of less technological days when you had to get creative to make a mix tape from "borrowed" cassettes or maybe songs off the local broadcast station.

Hopefully this modern solution may give you some ideas on getting more from your DMR radio.

Getting back to Kraken

After all that, now we can finally get to the recording you might have missed! 

Here is an MP3 recording mostly of the segment from Steve K2GOG.  

It sounds like he missed a few parts but is otherwise complete. It looks like a time intensive operation to click on all recordings in order, so bear that in mind if you wish to do something like this yourself.

The recorder function works on any "over the air" DMR signal, so using it also to record simplex activity like what took place during the NEARFEST on US national DMR simplex of  446.075 MHz on time slot 1, color code 1 and talk group 99 is another idea.   

But, if you plan to record audio from Brandmeister you can also just use the "Hoseline" function and route that audio from a talk group into Audacity just as easily using virtual audio cables. 

And with that, I hope you are looking forward as much as Steve is to getting the new Kraken once its starts shipping in March 2022.

Why United States amateur radio can not evolve?

 

The title of this post sounds a little like a "Jeopardy" answer in the category of "Famous son inventors".  Probably, the question was "Beyond silencers, this son of a different American pioneer was also known for the growth of which hobby, which involves shooting things other than bullets into the air?"

1ZT: Getting your attention!

Its always easy to poke fun at the love of all things high frequency and possibly even one of the important founders of the Amateur Radio Relay League (ARRL) who we have to credit, much like the National Rifle Association (NRA), for embedding certain hobbies and perceptions into the DNA of Americans.  

This is none other than the old man himself, Hiram Percy Maxim, who is not only one of the co-founders of the ARRL, but also one of the early inventors of the firearm silencer and son of the mastermind behind the Maxim machine gun.

Did you know there was a more legitimate co-founder of the ARRL named Clarence Tuska?  He was also the person behind the much loved QST magazine and likely would be more apt to read an article like this compared to Mr. Maxim.  

Both of these "OM" helped evolve the world of wireless communications for hobbyists like us, but we are now at a time where we need to prevent us from facing extinction.

As an engineer,  Mr. Tuska is who promoted the use of the higher 200m and above spectrum rather then the lower 600m band and was much more focused as an experimenter with radio technology.  I like Mr. Tuska and what he did for the hobby in the United States, thanks to his awareness to share information in written form. Lets now jump into something fresh and new! 

Why?

I write this after sharing notice of an important evolution within radio technology which has not yet really come into wide spread use across amateur radio yet.  

Today, we can not wait around for QST to learn about the latest innovations.  Its right here in the digital domain is where you will learn about something new. And, by the time most people get QST in the mail, its out of date and more time is spent trying to find who to give it to! 

The Future.....

What I am talking about is known as a software definable front end preselector.  Those I shared this latest Crowd Supply project with immediately needed to point out that something like this is useless, since it does not include capability for our much beloved "HF" spectrum allocations.  

At $419 USD, it is expected to cover spectrum much lower in order to appeal to the amateur radio hobbyist to make it a worth while purchase.

This preselector is a versatile, highly useful tool for providing programmable bandpass filtering for a software-defined radio, among other applications. 

In the receive path, that filtering can be used to mitigate the effect of strong blocking signals; in the transmit path, it can be used to help reduce out-of-band radiation. 

ATEK1001 aims to provide an affordable filter bank for radio enthusiasts and SDR users. More of the technical specifications concerning the 485MHz to 7.7 GHz can be read about here. 

Starting so high into UHF spectrum even limits its applications for most of the amateur radio community members interested in bands such as 70cm, 1.25m, 2m, 4m, 6m and of course the rest of the HF band.

What makes the ATEK101 interesting is how small it is. 

Who cares. More money for another HF CW/DIGI Kit!!

For those interested in Software Defined Radio (SDR), this is where the market software defined radio front end (SDRFE) is really targeted.  Not the HF only operator who only chases CW contacts in South Dakota.

The popular Lime SDR and Lime SDR Mini are joined by a branded product also available via Crowd Supply called the Lime RFE which does cover the important spectrum we care about and is only a mere $699 USD and covers up to 3.5 GHz plus all the important amateur radio bands in between. 

It is however a much larger product. There is even a $549 USD option for those who do not need the cellular filtering and this will appeal more to frugal amateur radio operators looking for something new. 

If you wanted to experiment with RF filtering, the Lime RFE or the ATAK1001 are what is available today.   

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SIDE NOTE:   Interested SDR for HF?   Get online for the QDX available October 11th at 2:00 PM EST until units sell out.   https://qrp-labs.com/qdx.html 

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Do I need a SDR Front End?

Reason here is to illustrate there are some interesting things taking place within the world of software "re-defined" radio worth keeping an eye on, but another area is the niche that the phase coherent software defined radio is filling.

We are jumping to a totally different topics here because I can not find anything about a dedicated HF only or even HF and VHF RFE to write about, but now I know I have your attention.  

A phase coherent SDR is a combination of multiple software defined radios which can act together or separate from each other to do interesting things.

Combining multiple receivers can act as a way to filter or combine signals and the RTL-SDR.com provided "Kerberos" product was the first low cost way to do this with its four receivers which are identical in performance to the popular RTL-SDR V3 most who are reading this probably own already.

Software for Software Defined Radio

A challenge when the Kerberos first came to market in early 2019 was little available software to use it with and it also needed a little more horse power from a computer to utilize its capabilities.

Things changed for Kerberos when the Raspberry Pi 4 became available and it was far easier to use the Kerberos for applications like radio direction finding or using its phase coherence capability. 

Software also improved since 2019, with applications like SDRangel being one of the first to offer easy to use multiple receivers at the same time in a visual application.   

Using something like a Kerberos and its 4 separate receivers capable to tune to any approximate 2.4 MHz chunk of spectrum at one time means you can monitor multiple bands at the same time or even the same frequency via different receivers and find ways to optimize reception by using different DSP filtering tools.  

By the time many people got excited about the capability of the Kerberos, it was already out of production or sold at lower cost, but there is a new model called the Kraken about to be unleashed which will include five independent receivers.  so,  its time to jump onboard now if you want to do amazing things with a phase coherent receiver. 

There is a more polished software program specific for the Kraken, which can also be used with the Kerberos if you have.  

Many more traditional SDR programs like those which Rick W1RHS let us know about recently also exist now which can be used with phase coherent hardware.

During the October 19th session of the popular Northstar Digital Net managed by Jim WA2UMP,  some discussion about both phase coherent receivers and possibly other SDR topics like RFE will be mentioned. 

Steve K2GOG of HVDN will be available to share more details and field questions on some other aspects about software defined radio that hopefully, will make the likes of Mr. Tuska and Mr. Maxim proud. 

Please be sure to join us Tuesday October 19th at 8:00 PM Eastern Time on Brandmeister Talk Group 31630 if you are interested in topics like this on the evolution of amateur radio by using the future to do so thanks to DMR.

Learning about SDR with Rick + Get ready for the Kraken!!!

Software Defined Radio is eating the world.  SDR devices have become common place in both the amateur radio and electronics hobbyist world for many years now and the good news is that hardware comes at different prices in order to appeal to different users.

On October 5th 2021 during the North Star Digital Net,  Rick W1RHS, will be talking about the inexpensive RTL-SDR USB dongles and where they fit in along side other much more expensive devices aimed at the amateur radio community.

For under $30 USD, this popular RTL-SDR V3 has been covered before on HVDN and Carl Laufer who is the manufacturer of this SDR has even shared some HVDN articles on his very popular RTL-SDR.com blog

And, because HVDN and Jim WA2UMP who runs this excellent DMR weekly discussion are close friends with Rick W1RHS, here is a quick link to Rick's upcoming presentation which will be live on talk group 31630 (STEM) on Brandmeister next Tuesday.  

Its also possible to listen to the discussion without a DMR radio by looking for 31630 in the talk group list at https://hose.brandmeister.network/#/ 

What about the software?  What about the Kraken?

Rick covers some really great detail on hardware plus some ideas for software, which is really needed to get your "software" defined radio to do anything.

Between Rick's latest presentation and one that Steve K2GOG did a while back on "Sensing the world around you", you will see many of the same references to certain software, like SDR#, SDR Play, SDRangel and a few others. Since the below chart was created, another cross platform application worth a strong look is called SDR++

One area which both presentations did not talk about is something called a phase coherent software defined radio which actually combines multiple radio's together in order to provide very unique capabilities.

The RTL-SDR.com website not only offers its inexpensive SDR many just call the "V3" but also a device called the Kerberos and its upcoming really exciting update to this called the Kraken. 

This topic on phase coherent SDR is best left for another time, like how to change some code to use the older Kerberos hardware with the newer software meant for the Kraken.

Please give a listen to support Rick and his October 5th SDR presentation by marking your calendar now incase you have other things in the Hudson Valley or beyond taking place the same evening.

Easy SDRangel: Windows Executable

Been a fan of Evariste's SDRangel project for a long while now and it has been hard to convince many how amazing his opensource wizard work has been.

Unless your a Linux master, which I am not, you had to figure out how to find an already compiled Microsoft Windows version in the Git repository or get all the right dependencies working under Ubuntu or whatever Linux distribution you roll with.

Well guess what?

Rather than than go here: https://github.com/f4exb/sdrangel/releases and look for the correct links and follow instructions like this old HVDN December 17th 2017 article entitled "SDRangel & Decoding Digital Voice (DMR, D-Star, Fusion, etc)", how about we just cut the bull and give you what you have wanted for so long dear SDR fans.

With SDRangel v4.11.0 you can now just grab sdrangel-4.11.0-win64.exe

This will install just like any other Windows application on a 64 bit modern machine and I need to say,  the final result is a very, very responsive piece of software.

Installed, now what?

If you have an el-cheapo RTL-SDR dongle from China for under $9 USD or the much better quality and legitimate version RTL-SDR v3, Kerberos SDR , any of the Lime SDR products, Hack RF, etc you will be able to use them all easily with SDRangel v4.11.0, even all at the same time if you want!

Lets start by making sure SDRangel will find the SDR you have plugged into your computer. Yes, do that now and then click where the arrow points to. The example below is with a generic USB SDR dongle.

Monkey see, monkey do

Now that you have things installed and selected a demodulator, time for some fun. You can do the following:

• Listen to stuff 
• View stuff
• Visualize stuff
• Decode stuff
• Record stuff
• Stream stuff

Lots of stuff. Have fun with SDRangel on Windows. Do we need more of helper monkey at HVDN? 

LimeSDR Mini & SDR#: Yes, it works....

Of all the SDR programs, SDR# still holds a special place in my heart. Until recently, it was hard to get the LimeSDR Mini working with this versatile piece of software.

Lucky for us, Goran Radivojevic (YT7PWR) has done some recent great work to make these two software defined radio things play nice together.

Step 1:  

DownloadSDRSharpLimeSDR_v02.zipfrom https://github.com/GoranRadivojevic/sdrsharp-limesdr/releases and unzip the folder content into where your version of SDR# is found. There are 3 files:

Step 2: 

Add the following line in the frontendPlugins sections of FrontEnds.xml file:

<add key="LimeSDR" value="SDRSharp.LimeSDR.LimeSDRIO,SDRSharp.LimeSDR" />

Step 3: 

Plug your LimeSDR Mini and load SDR#.  I am using release 1700. You should see LimeSDR in your drop down options under "Sources" just like where you would select RTL-SDR (USB).

Step 4: 

Click on the gear icon to open the setting for the LimeSDR Mini and hit the "refresh" button.  You should see the details for your LimeSDR Mini come up as pictured below.

Comments:

With the LimeSDR Mini attached to a laptop via a 6 foot USB cord, reception was fine with my "test setup". The signals shown on SDR# for the curious were two of my MMDVM hotspots operating on 427.585 MHz single slot  and 427.545 MHz dual slot running DMR mode. I pipe audio out of SDR# into DSDplus, but generally I prefer the simplicity of using SDRangel for decoding digital voice modes. Dragorn of Kismet fame printed the nice case for my Lime SDR Mini a while back.

Steve K2GOG

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Recent HVDN Notebook articles worth a look: 

• NXDN: What is it and where is it?

• Line of Sight: Aircraft Edition

• May 2019 Global Digital Repeater Roundup

• Timing is Everything: 7 Days with Kerberos SDR

Timing Is Everything: 7 Days With Kerberos SDR

The long awaited Kerberos SDR arrived last month, but I only recently got a chance to really focus my full attention on this unique device this past week. This article covers my first impressions plus setup helpful tips.

What is Kerberos SDR?

A successful Indiegogo campaign which netted 8007% backing sort of is a big deal in my mind and makes for a nice introduction statement.  The Kerberos hardware and software package was under development for some time and required many people to be involved as covered in a past article in the HVDN Notebook focused on tracking radio signals this past November.

Software defined radio has been top of mind in the hobby community for some time, thanks to inexpensive USB TV tuner dongles that have found a dual purpose as wide range radio receivers, such as the RTL-SDR v3 or NooElec and its various offerings for around the same price.

The Kerberos SDR is at its core, four of these inexpensive and capable SDR receivers assembled into one circuit board along with a number of modifications and upgrades to enable some interesting applications.

As the title of the article implies, timing is everything. At the core of the Kerberos is a shared TCXO clock source which ensures all four independent receivers are synchronized with a high degree of stability.

Last month at TCF, Joe N1JTA showed how important a TCXO is to the MMDVM "hot spot" boards that amateur radio operators are using as part of modern digital voice communications.  This same concept applies with the Kerberos, but essentially on steroids.

Having synchronized receivers allows some real fancy computations to be made using newly created open source software that is packaged with the Kerberos SDR.

Computational you say?

There is an already a well written and detailed quick start guide for using a ready made disk image or how to install the packages and related dependencies to get the Kerberos SDR software up and running, so no need to rehash that here.  But, in order to get the most out of this phase coherent software defined radio receiver, here are a few tips.

     Hardware related

• Power source considerations:  Just like with the MMDVM Pi-Star hotspots, DO NOT use some old 500 mAh USB charger from an ancient Palm Pilot!  The Kerberos SDR needs its very own 2 amp or higher current USB power source that will connect into the USB C port. This is to power all 4 receivers and not for data transfer.  A best practice is to use a separate power source for the Kerberos SDR and another for the single board computer running the demo software.

• Connecting things together: The order you connect things together does matter.  Follow these steps to avoid frustration. First, connect your power source to the Kerberos and let it run for a minute or two.  DO NOT yet connect antenna or USB micro cables to the SDR.  If you peak carefully inside the SDR near the USB connectors, you will see white LED and blue LEDs flickering inside to tell you the Kerberos is powered up.  Second, now it is safe to connect a USB micro cable from the SDR to your compute device. If using the recommended RPI 3B or 3B+,  your third step should be to apply power to the RPI after you have inserted the SD card.  Reasons for this order explained later.

• Calibration:  Try not to bug some of the innovators like Corrosive from the popular SignalsEverywhere "vlog" with basic questions so he can find some more new cool stuff to tell us all about even though he may not mind your questions.  Perform the calibration using the built in noise source and 50 ohm terminations your Kerberos came with. DO NOT skip this step.  Not only will you learn more about the software in the process, but you will avoid frustration when testing out direction finding or passive radar functionality.

• Antennae:  You need four identical antennas.  My initial tests were conducted with these small magnetic mount antennas designed for near the 70cm frequency band.  The real key is identical antennae, especially for the signal location application.  The passive radar application would likely benefit from one directional and one non-directional antenna instead, thus two antennas only are needed for that application.   It would also make practical sense to source some type of metal plate if using magnetic mount antennas, so be sure to order an iron pie plate from Amazon too when ordering antennas if you do not already have one handy. Placing magnetic mount antennae on a ground plan makes a huge difference.

• Temperature:  If you have already experimented with single SDR dongles, you know they get a little hot.  The Kerberos SDR will also run warm to the touch and is normal. If using the SDR for an extended period of time, you may want to invest in a small fan to keep it cool. 

• Raspberry Pi:  The image provided on the quick start page is for the RPI 3B or 3B+.  It will not work correctly with an older Raspberry Pi, so save yourself the trouble. The software is also somewhat intensive, so either run the Kerberos on an RPI3 or a real computer. DO NOT try to use an older SBC or anything not supported that is under powered from a CPU perspective. 

• Taking Kerberos SDR apart:  You will be tempted to take Kerberos apart. DO NOT do it unless you have a good reason to do so.  The 40 pin header under the Kerberos is an alternate way to connect a RaspberryPi with an extended header, but is really not needed.  If you did want to do this, you WILL need to open your Kerberos up and remove a 2 pin jumper inside after almost total disassembly.   Also, that tempting regular size USB port is for future use and will not work UNLESS a pair of chip resistors are removed inside the Kerberos SDR.  The bottom line is, just focus on how Kerberos is configured before thinking about hacks and modifications and get the most out of the hardware as it arrived to you first. 

      Software related

• Demo software:  Its not very polished, but gets the job done.  The biggest thing to be aware of is that your Kerberos WILL NOT work if you did not plug in everything correctly first.  If you see no sample rate with numbers being displayed in milliseconds or seconds, you did something wrong or do not have the right power source or good USB cables.  Do not blame the software first, check your hardware. The software is otherwise pretty straight forward.

• Computational stuff:  You may learn quickly that the RPI 3B+ is under powered at times if you are running wider bandwidth than the default setting of 250 kHz. You can trim this down closer to the width of the signal you are interested in.  You can also change the decimation from its default to any higher number for slower sampling speeds. Both changes will give you lower latency overall.   Same goes with shutting off the spectrum display as it does take a number of compute cycles to visualize 4 simultaneous views of the frequency being monitored. 

Additional stuff

There will be future articles about direction of arrival and passive radar related topics here on HVDN Notebook related to the Kerberos SDR as well as experiences running the demo software on a much more capable piece of computing hardware, but for now follow all these tips and best practices.

Feel free to share your experiences on the RTL-SDR forum for Kerberos SDR and enjoy your new toy. 

Basic Overview: Tracking Radio Signals

Finding the source of a radio signal is sort of a fun thing to do for the modern electronics hobbyist.

Confirming the location of a local FM band music broadcaster, amateur radio station or even your cell phone and maybe your car keys is possible with relatively inexpensive equipment since they all transmit RF energy!

With the much anticipated KerberosSDR nearing availability, which will provide unique radio based location capabilities.

Something unrelated recently reminded me to go back to have a look at RTLSDR_Scanner and its latest developments since it offers a lot of great functionality for those interested in radio signal location options available today.

Both solutions use a software defined radio or SDR rather than a traditional radio. This is one reason that makes both of these solutions really exciting!

The conclusion of this article will show you how to generate a map such as the one below that will show signal/power measurements called an "RF Heat Map" using RTLSDR_Scanner.

Kerbo What?

The well funded IndieGoGo campaign of the phase coherent software defined radio that Carl Laufer of the excellent RTL-SDR.com blog, the design team behind the now named Othernet Project and Tamás Pető who is studying electrical engineering at Budapest University.

This trio has created something that will be able to do some amazing things, but let's first take a look at basic radio signal location theory and another modern radio signal location tool.

What is phase coherence?

Let's first look at some basics of radio signal location through some easy to understand math.

If two people (1 &2) knew exactly how far apart they were  (A) and had directional antennas that could help find the maximum signal strength of a transmitter (3), they can use the angles of the signal direction and the known distance between them (A) to guess pretty closely on the approximate direction and distance (B&C) of the signal source (3).

This method of signal location is called triangulation.Radio signals travel at about the speed of light which is about 982 million feet per minute. 

If our two friends standing at location 1 and 2 had identical and synchronized clocks and had radios tuned to the frequency of the transmitter at 3, they could also determine the direction of the signal by moving around a little to see how the signal strength fluctuates, they could also determine the general location of the transmitter with a little more help by use of doppler theory.

Doppler works by sensing how a received signal's frequency (2) fluctuates up or down based on the speed it is traveling and how long it takes to go from source to receiver (1). with multiple antennas (A,B, C, D) .

If multiple receivers/antennas are used at the same time, the difference in time it takes to be received at each can be used to calculate a direction of the signal.

Some form of very fast analog or digital computing and comparison that is part of the receiver is needed since we are talking about nano or millisecond differences.

Phase coherence combines theory behind the speed of which radio signals travel against a known time source along with triangulation in order to find where a signal is coming from.

Police departments have been using a phase coherence system to locate stolen cars for many years called LoJack.  

If you look closely at the roof of the New York State Police cruiser above,  the four antennas on the roof spaced in a square pattern roughly about a foot apart help perform the triangulation and time difference of arrival (TDOA) measurements to quickly locate the stolen vehicle. 

All the police officer generally needs to do is view a display not too different from a no longer in  business company that offered a device called the Ramsey DDF-1 Doppler Direction Finder.

The doppler method of signal location involves the ability to visualize the arrival angle of signals relative to one another of equally spaced antennas through the use of a series of LED lights spaces in a circle pattern.

A special circuit compares the received signal strength at each of four antennas relative time or direction of travel in order to give the direction towards the signal

As the police car travels, the LED lights would blink in the direction where the signal is coming from, if it is in one location. This would tell the officer (or amateur radio operator) which way a signal was coming from and they could try to get close to its location.

Once close enough to a signal, other methods could be used such as a field strength meter to find the smallest of hidden transmitters or chopped out hidden LoJack units. 

HVDN Field Strength Meter Monday is coming back. 

Here is where it started and where it is headed next

Twenty or more years ago, doppler based analog solutions were almost as fancy as one could get in locating transmitters.

In 2018, however, things have come a long way thanks to SDR and even embedded computing devices like the raspberry pi, which can also be used to run RTLSDR_Scanner and the KerberosSDR.

Heat Maps and GPS

The RTLSDR_Scanner application is a little more simple than KerberosSDR. An inexpensive software defined radio (SDR) receiver along with a GPS USB dongle can be purchased together for less than $40 USD.

KerberosSDR, is essentially four SDR's combined into one unit, so should also be able to use the RTLSDR_Scanner software too.

The SDR and GPS along with one antenna, a computer (laptop or Raspberry Pi) and the appropriate software can perform some interesting signal location applications.

GPS provides the function of providing accurate location of the receiver along with a stable time reference.

The locations coordinates, exact time and signal strength of the signal can be combined to provide stunning visualizations of how strong or weak a signal is on mapping programs such as Google Earth

Lets get SDR_Scanner working

In 2016, this program was only operational under a linux computing environment, so was not easy to set up unless you were very involved in computer "stuff".

This program has been available as a much easier to install Microsoft Windows version since last year and is finally what this article is about!

You will need the following hardware and software along with a little patience and clear mind.

Hardware

• SDR dongle (Suggest the RTL-SDR v3, but pretty much any will work)
• USB GPS with NMEA output (Suggest the uBlox7 Gmouse)
• Modern Windows Computer (Meant to run Win7 or later!!)
• Antenna for frequencies of interest (Most SDR come with a basic antenna or add on options)

Software

• RTLSDR_Scanner Software (Versions are clearly explained on Al's website)
• ublox u-center test software (Optional, but nice to have anyway)
• SDR# Receiver Software (Optional, but you should have this already, right?)
• Google Earth (If you want to see the real time location of signals on a map, you need this)

First, lets make sure your SDR receiver is functional.  The best tutorial on this can be found here.  

Step 1:  Get your SDR working:  https://www.rtl-sdr.com/rtl-sdr-quick-start-guide/ 

Try listening to some FM broadcast music between 87-108MHz,  weather broadcasts in the 162.4 to 162.6 MHz range or for local amateur radio or business/first responder activity between 420-500 MHz.

Now, let's get your GPS working

The USB GPS should automatically recognize and install drivers for most people on a Windows 7 or 10 computer.

After installing the ublox center program and just playing around with it to show it can receive location data, make a note of what COM port the GPS has decided it will use. 

Note:  The GPS obtains a virtual serial port over USB. You DO NOT need any outdated USB to 9 Pin serial adapter.

The instructions for getting RTLSDR_Scanner are cracking fantastic, so give them a read here and you should be up and running fairly quickly

Step 2:  RTFM = RTLSDR_Scanner Instruction Manual

Try tuning to local weather or music broadcasts to see what activity looks like in a one megahertz wide segment would look like.

The above image shows from 162 to 163 MHz, with a very powerful signal located at 162.475 MHz (Local weather broadcast) and how the signal fades slightly over just a few seconds from 12:04:19 to 12:15:50 due to driving around at a slightly variable speed.

A pinch of GPS and a cup of Google Earth

Now that you have a feel for how the GPS and SDR with RTLSDR_Scanner function, lets combine the two now by enabling GPS data to get combined with RTLSDR_Scanner output.

Below is what exporting the RF signal data looks like over the same 11 minute period when combined with GPS location data as output against Google Earth map.

Step 3: Use this opportunity to install Google Earth if you do not have it already. 

You will need to enable GPS under the "Edit" menu of RTLSDR_Scanner and ensure you change GPS type to "NMEA (Serial)" and select the COM port your USB GPS has.

When everything is configured correctly, you can use RTLSDR_Scanner to show what GPS satellites are being received and also when you get a location lock, your GPS coordinates and altitude will appear in lower right part of the application.

All that is left now is to go drive (or walk?) around with your laptop and start taking some measurements.

Depending on the refresh rate (dwell setting) and resolution (FFT Size setting), the output image on Google earth may vary.

Helpful Note:  Be sure to set mode to "continuous" and not try to sweep too wide a frequency range. Keep it to the smallest based on the signal you are looking for.  YOu also need to indicate how many sweeps to perform or otherwise, it will just keep overwriting the previous sweep which is not very valuable. The minimal setting is 1 MHz. This will help create the best results viewed on the map. To generate an the images in this article required 115 continuous sweeps.

Major benefits with RTLSDR_Scanner 

Here is a list of possible real life user cases that this application will enable:

• Creating a coverage map for amateur radio repeaters in the 144, 220, 440, 900, 1200 bands

• Determining general radiation patterns of a mobile or home amateur radio antenna installation

• General location awareness of commercial radio or broadcasters

• Interference source location finding

• Figuring out the range of your garage door opener or other pulsed mode transmissions

• Basic passive radar system

Sadly, RTLSDR_Scanner is not really designed as a Wi-Fi mapping tool, but by playing around with the dwell setting and using a device like a LimeSDR Mini, HackRF One or ADALM Pluto which are more expensive could give interesting results.

These other SDR options can go to about 6 GHz and not covered by the inexpensive SDR dongles that usually do not go too far past 1.9 GHz plus monitor wider bandwidth of up to 30 MHz wide at one time compared to the 3 MHz wide capable RTL SDR v3.

So what is special about KerberosSDR?

For the price of under $150 USD, users will be able to use the hardware and software along with four antennas to generate a heat maps just like RTLSDR_Scanner and also show signal direction using phase coherence theory through new software that Tamás Pető is focused on where an early version is demonstrated here:

Hope you found this article about basics of radio signal location interesting and something to keep you occupied while HVDN awaits its pre order of the KerberosSDR which will then be reviewed here later this winter.