SDRplay Spectrum Analyzer Alpha Version Released

Steve Andrew has just released an alpha version of a Windows Spectrum Analyzer app for SDRplay SDRs that he's been working on. The app is currently still in alpha, meaning that all the features are not yet implemented. In particular, scans larger than the SDRplay's maximum bandwidth of 10 MHz are not ready yet. In the future the app will be able to scan swath's of bandwidth up to 2 GHz wide, similar to what SpectrumSpy for the Airspy and rtl_power for the RTL-SDR does.

We are pleased to announce the availability of the first cut of Spectrum Analyser software developed by Steve Andrew specifically for the RSP line of products. Please note that this is first alpha software and so it is still very much in development and some features are still to be added. Currently supported are:

RSP1
RSP2/RSP2pro
RSP1A

This first alpha release gives a good idea as to the look and feel for the software. The main functional limitation is that sweeps of greater than 10 MHz are not currently supported. Steve is currently re-working the algorithms for providing wider sweeps than 10 MHz to improve sweep time and remove the issue of the DC spike in ZIF mode, so please bear with him.

We recommend using the software with AGC turned off and use manual control of the gain for better display stability.

Please use this forum thread to post any issues. Read the issues already raised and only post if the issue you have found hasn’t been raised. This will help Steve in his development.

Further development information can be found on the forum.

Click here to download the 0.9a Alpha release.

SDRplay Spectrum Analyzer Alpha
SDRplay Spectrum Analyzer Alpha

Browsing the UHF Satcom Band via SpyServer

Over on YouTube Corrosive has published a video of him browsing through the UHF Satcom band with a remote Airspy SDR being streamed via SpyServer. The UHF-Satcom band is anywhere between 243 - 270 MHz and contains fairly strong signals from many several US satellites that can be received with a simple antenna. Some of the satellites are simple repeaters without security, and pirates from Mexico and South America often hijack the satellite for their own personal use. So it can be quite interesting to look for pirate conversations and sometimes SSTV images. Reception of these satellites is generally available in Canada, US, Mexico, South America, Europe and Africa.

UHF Satcom Transponders Close Up on the Airspy SDR
UHF Satcom Transponders Close Up on the Airspy SDR

CrowPi: Raspberry Pi Experimenters Kit Review (With RTL-SDR and RPiTX Tests)

CrowPi is a Raspberry Pi all-in-one experimenters kit that is currently crowd funding on Kickstarter. The idea behind CrowPi is to combine a touchscreen, various sensors, actuators and interfaces into a clutter free kit mounted on a PCB in an easy to carry hard shell case. It's mostly intended to be used in STEM learning environments, however it could also be used for rapid prototyping of Raspberry Pi based ideas, or simply as a portable computer. 

The CrowPi
The CrowPi

The kit has 4 days left on Kickstarter and has already met its minimum goal. Pledging $1,169 HKD (~USD $150) gets you the basic kit which does not include a Raspberry Pi. Higher pledge levels (up to US$250) get you models that include a Raspberry Pi as well as extras such as a 5V power supplies, earphones, heatsinks, keyboards, game controllers etc. Shipping of the units is expected to commence in July.

Elecrow, the Shenzhen based company behind CrowPi kindly sent us a free kit for an honest review. While not directly related to RTL-SDR or RF, we thought that there might be several applications that might make the CrowPi kit useful for prototyping some simple low cost RF based ideas. For example:

  • Prototyping IoT based modules that use the RTL-SDR as a receiver. For example receiving a 433 MHz ISM signal and writing received information to the LCD/LED array or activating the relay.
  • Similarly, using FL2K-SDR or RPiTX to transmit a signal when a sensor is activated, or to transmit telemetry from that sensor (e.g. distance data from the ultrasonic sensor, humidity levels from the DH11 sensor, or light levels from the light sensor)
  • Using an RTL-SDR to prototype an ADS-B plane camera tracker using the two servo module interfaces.

To get an idea of what's packed into the CrowPi, the kit includes the following modules:

  • Everything that came with our CrowPi Demo Kit (Except the Raspberry Pi)
    Everything that came with our CrowPi Demo Kit (Except the Raspberry Pi)
    1920 x 1080 Capable HDMI 7" Touch Screen
  • LCD Module
  • 8x8 Matrix LED
  • Breadboard
  • 4 character 7-seg LED
  • Vibration motor
  • Light Sensor
  • Buzzer
  • Sound Sensor
  • Motion Sensor
  • Ultrasonic Sensor
  • Servo Interface
  • Step Motor Interface
  • UART
  • Tilt Sensor
  • IR Sensor
  • Touch Sensor
  • DH11 Humidity Sensor
  • Relay
  • Matrix of buttons
  • RFID Module

With our kit we also received:

  • 2x GPIO Flex Cables
  • 1x Stepper Motor
  • 1x Servo
  • 1x Charger
  • 1x IR diode
  • 1x NFC Tag
  • 1x Mini HDMI for the Raspberry Pi Zero
  • 1x IR Remote control

Setup, Initial Testing and Thoughts

Setup: Setup was simple and consisted of downloading their customized Raspberry Pi image onto an SD card, connecting the Raspberry Pi to the HDMI, USB and GPIO pins, and then powering it up using the power jack on the CrowPi Board. A user manual is available for download.

Initial Testing: CrowPi provide a set of lessons that show how to use each of the modules on the board. All modules also have Python code examples that are ready to run as soon as you boot up. Immediately after booting up we were able to run their demo code which allowed us to test all the various sensors, print text to the LCD module, activate the 7-seg display, and actuate a servo and stepper motor. 

The tutorials are easy to understand and provide a good basic rundown of the sensors. You will need to have some basic Python skills to understand the Python code however.

Thoughts: The CrowPi is built sturdy, and is definitely easy to use. The touch screen is bright and clear. It is capable of running in 1080P mode, but is a bit too small and hard on the eyes to use at this resolution. We kept the screen in 720P mode. In order to use the Raspberry Pi, you'll need to plug in a USB keyboard and mouse which is not included in the basic kit. A wireless keyboard/mouse combo is ideal. There appear to be speaker holes next to the monitor, but it seems that our demo model is the basic model which does not include built in speakers. The kit is impressive looking and appears to be priced reasonably for what you get.

RTL-SDR and RF Testing

Unfortunately when it came to run the RTL-SDR we instantly ran into a problem. With the one 5V 3A power supply running the Pi, HDMI Screen and modules, it seems that there just isn't enough power budget left over to run the RTL-SDR which draws about 270 - 290 mA current. The RTL-SDR connects fine, but when trying to run GQRX, the Pi 3 shuts down. To get around this problem we have to connect a second power supply directly to the Raspberry Pi 3's input. After doing this the board and kit runs smoothly with the RTL-SDR. Using a powered USB hub would also work.

RPiTX is software for the Raspberry Pi that allows you to transmit RF signals directly via PIN12 or PIN7 from the GPIO ports. On CrowPi PIN12 is already connected to the buzzer, and PIN7 is connected to the humidity sensor. Using PIN12 causes the buzzer to sound, so we tried PIN7. Even though it's connected to the humidity sensor, it doesn't seem to mind the GPIO bit flipping going on. The traces within the board and cable radiate sufficiently to transmit signals strongly enough to use within a room, so no external antenna is needed. Use of PIN7 can be activated in RPiTX by using the "-c 1" flag.

Using our Replay Attacks with an RTL-SDR, Raspberry Pi and RPiTX tutorial, we copied  the signal from the remote control of a 433 MHz alarm/door bell, and used RPiTX to replay the signal. Then by modifying some of the supplied CrowPi Python code we were able to get the doorbell to sound on a touch of the touch sensor, activation of the sound sensor and via activation the RFID sensor. We could see the CrowPi being used as a general tool for learning how to prototype simple IoT or home automatic devices. The video below shows a brief demonstration. 

It would have been nice if these RPiTX GPIO pins could have been exposed, and not connected to a sensor, but the developers of the board had probably not heard of RPiTX as the goal is for a more general classroom application.

CrowPi Demo
CrowPi Demo

Conclusion

If you're looking to get kids or STEM students/hobbyists interested in what Raspberry Pi's can do, then this kit couldn't make it simpler. The single board and briefcase design makes the whole thing very tidy and portable and the kit looks and feels sturdy and professional. If you know a kid interested in electronics, then this kit would make a great present.

You could probably purchase all the components cheaper individually, but at the end of the day an all-in-one kit just makes sense as it is a lot tidier, and much easier to get up and running quickly.

For RF experiments, it's possible to use the RTL-SDR with the minor annoyance of having to connect two power supplies or use a powered USB hub. RPiTX also functions fine on the device and can be used to transmit an RF signal on activation of any one of the sensor modules. This could easily be used to prototype simple home automation or IoT ideas.

Osmocom now accepting Donations

Osmocom, the team behind the original RTL-SDR driver project, the Osmo-FL2K discovery, OP25, gr-osmosdr, gr-gsm and various other open source cellular phone projects is now accepting monetary donations. If you weren't already aware, it was the efforts of Antti Palosaari and Eric Fry who made the original tests on DVB-T dongles, and then Osmocom who wrote the first RTL-SDR driver and software that is still currently used in the RTL-SDR project today. If you're interested, there is a full write up on the history or RTL-SDR at the bottom of rtlsdr.org.

Recently Osmocom have begun accepting donations via Open Collective. They write

The Osmocom project (if you count its predecessor OpenBSC) have been running for close to 10 years, creating a large number of Open Source projects related to mobile communications. We have never needed nor wanted any legal entity for it. It's a pure/classic FOSS project, open to contributions from anyone.

Until today, you could only contribute in one of the following forms:

  • by writing code (bug fixes, new features, etc) and submitting it (which means you need to be a developer)
  • by writing documentation / improving the wiki
  • helping other users on the mailing lists, IRC, or in other forums
  • donating cellular equipment (which many don't have)
  • hiring a freelancer or a company to write code and contribute to Osmocom on your behalf 
  • buying products or services from companies who dedicate lots of work to Osmocom

However, we've repeatedly getting requests from some individuals who wanted to contribute to the project in an easy way, even if they are not a developer, and/or don't have time, and/or don't have the size of a budget to fund development of entire new features or sub-systems.

Today, Osmocom announces that we have joined Open Collective in order to enable you to make financial contributions, either one-off or recurring.

We'll be using the funds (if we get any!) according to our funding policy outlined at https://opencollective.com/osmocom/expenses/new# in order to pay for expenses such as hosting costs for our servers / IT infrastructure, travel funding for the annual developer conferences, etc. Any and all expenses paid from those funds will be visible on the OpenCollective website. You cannot ask for more transparency than that :)

Thanks in advance for your kind assistance!

So if you've ever enjoyed the RTL-SDR project, and how much it's improved your access to the RF spectrum, please consider donating via Open Collective or contributing back in other ways. Donations may help Osmocom to continue making new and interesting discoveries, such as Steve M's amazing FL2K-SDR discovery that was released back in April this year.

Controlling moRFeus over a Network Connection

Thank to LamaBleu for submitting news about his new software for the moRFeus signal generator and frequency mixer called moRFeus_listener. The software allows you to remotely control a moRFeus device via Telnet, TCP/UDP or HTTP. This could be used to control the moRFeus in a similar way to the short script that we used for generating a tracking tone in our previous tutorial on using measuring filters and antenna VSWR with the moRFeus.

LamaBleu also shared his results with using the harmonics of the moRFeus to generate a signal well past it's upper frequency limit of 5.4 GHz. He writes that by using the third harmonic is was able to generate a CW signal at 10.8 GHz and that tones up to harmonic 11 seem to work well. 

Running Osmo-FL2K on VMWare Workstation Pro

Thank you to Sajjad Golchin Poor for writing in and letting us know about his success with getting Osmo-FL2K to run in WMWare Workstation Pro. Osmo-FL2K is a driver that enables very cheap VGA dongles to work as a SDR transmitter. Previously in our initial first tests with the FL2K-SDR we discovered that it wouldn't connect to a Virtual Box virtual machine, but theorized that it might work in the commercial (non-free) version of VMWare as that has known working USB3.0 support. Regarding his tests in VMWare, Sajjad writes:

...I started working with Virtualbox but as you said the USB 3.0 drivers have some problems and cannot disconnect dongle from the host and attach back to the guest. 

So I went for VMWare Workstation Pro 14 and after booting the GNU radio live image and attaching the dongle and installing the drivers it worked perfectly at transmitting WBFM on the virtual machine. For permanent use of dongle I downloaded and installed Ubuntu 16.04 latest version and it is working flawlessly right now on the VMWare.  

Something that I realized during my test was that the maximum achievable sample rate in VMWare environment is a little bit lower (by Max. 10Ms/s) than what was expected but I guess it is ok for most applications. (it may be because of VMWare USB 3.0 drivers.)

Another thing that I came up with was that some sample buffers may drop during the delivering process to FL2K and it can ruin the whole transmission process. for example, when I was transmitting WBFM after a few minutes it stopped transmitting without any warning/error in the console and the machine thought that it is delivering the samples right to the device. It happened to me both in the VMWare environment and GNU radio live bootable so it might be a software issue.

Sajjad also that he's able to achieve sample rates of at least 145 MS/s in VMWare, but that maximum rate that it locks at always seems to vary between 145 - 157 MS/s

We have been wondering if anyone else has been successful in getting an FL2K dongle to run smoothly in a virtual environment? If you have please post in the comments.

Examples of compatible Osmo-FL2K USB to VGA Adapters.
Examples of compatible Osmo-FL2K USB to VGA Adapters.

moRFeus Half Price Sale: $99 Signal Generator and Frequency Mixer

moRFeus is a low cost wideband signal generator and frequency mixer. It can be used to generate a tone anywhere from 85 MHz to 5400 MHz, and can also be used as a frequency mixer, allowing you to implement upconverters and downconverters. In past posts we've reviewed and seen it being used as a PC based signal generator with open source GUI's, downconverter, CW generator, and most recently as a tracking generator for measuring filters and antenna VSWR.

Currently Outernet are having a half price sale on the moRFeus. Normally it's US $199, but now with the coupon code "rtlsdrblog" it's only US $99. The sale only lasts until Saturday 09 June 2018, so get in fast if you want one.

moRFeus can be purchased from the Outernet store.

Update: Please note that the sale has now concluded.

moRFeus coupon "rtlsdrblog"
moRFeus coupon "rtlsdrblog"

Using an RTL-SDR and moRFeus as a Tracking Generator to Measure Filters And Antenna VSWR

The Outernet moRFeus

As Outernet is currently having a sale and selling their their moRFeus product at only US $99 (see next post for details - or simply use coupon code "rtlsdrblog" on their checkout - valid until Saturday 09 May 18), we thought that we'd show an interesting use for the moRFeus when combined with an RTL-SDR.

Outernet's moRFeus is a signal generator and frequency mixer that can be controlled either by it's built in LCD screen, or via software on a Windows or Linux PC. It can generate a clean low phase noise tone anywhere between 85 to 5400 MHz. Because it can be computer controlled it is possible to use moRFeus as a tracking generator for characterizing filters and measuring antenna SWR. A tracking generator is just a signal generator that can be set to output at the same frequency that the measurement receiver is tuned to.

In the past we've posted a tutorial showing how to use a wideband noise source for measuring filters and antenna SWR. However, if available, a tracking generator is usually preferred over a noise source. A wideband noise source outputs high power at all frequencies, and so can easily overload an RTL-SDR causing reduced dynamic range and accuracy in measurements. This is especially the case when measuring bandstop filters as they pass all frequencies, apart from a small blocking band. Since so much noise gets through to the dongle, dynamic range is reduced.

This post shows how to use the moRFeus as a tracking generator together with an RTL-SDR for making RF measurements. This could be called a scalar network analyzer. The set up uses GQRX and a Python script, but in the future it is possible that someone may develop a standalone app.

Equipment Required

  1. A directional coupler like the minicircuits ZFDC-20-5, or an RF Bridge with 50 Ohm dummy load.
  2. moRFeus or other computer controllable wideband signal generator.
  3. An RTL-SDR
  4. A ~20dB attenuator

Since the output of the moRFeus is quite strong, an attenuator is required to keep signal levels low enough to not overload the RTL-SDR.

The cheapest RF bridge we've found is available on eBay for about $7. With an RF Bridge you'll need a 50 Ohm dummy load as well to connect to the 'REF' port. Directional couplers seem to work more accurately however, and second hand minicircuits ones can often be found on eBay. A $2 TV 'tap' is also a directional coupler, and may also work, although we have not tested this.

Software Setup

In this tutorial we're using the method first described by 'LamaBleu' in his post to the Outernet forums. The method uses Linux and involves reading power levels from the RTL-SDR by using GQRX and it's remote telnet connection capabilities. The telnet command "F freq" can be used to change frequency in GQRX, and the command "l" can be used to read out the current power level in dbFS.

To control moRFeus we use Outernet's official "morfeus_tool",  which is a command line based tool.

A basic Python script was written to set the frequency in moRFeus and GQRX at the same time. After a 500 ms settling time the power level is measured and recorded in a CSV file, then the script iterates to the next frequency. We iterate at 1 MHz intervals.

If you have a moRFeus and want to try this project out, copy and paste the script from pastebin, and name the file morfeus_scalar.py. Place the morfeus_scalar.py file and the morfeus_tool_linux_x32 tool into the home folder.

To get the software started:

  1. Open GQRX and connect the dongle and required RF components for the test (shown below).
     
  2. Set the RTL-SDR gain to zero or just low enough so that the signal doesn't cause overload (moRFeus signal levels are fairly high).
     
  3. In the GQRX GUI ensure that the "Remote control via TCP" button is pressed in. (Looks like two computer screens).
     
  4. Edit the Python script and choose the frequency range that you'd like to scan by setting variable FREQ_MIN and FREQ_MAX.
     
  5. In a terminal run "sudo python morfeus_scalar.py".
     
  6. When the script completes you'll have a file "out.txt" which is a CSV file of frequency and signal power levels.

Characterizing Filters

To characterize a filter (find the response of a filter) simply connect the system like so:

moRFeus Filter Test
moRFeus Filter Test
  1. But first connect just the moRFeus, attenuator and RTL-SDR together.
     
  2. In GQRX increase the gain until just a few dB before the RTL-SDR overloads and starts showing signal images. This will maximize the available dynamic range.
     
  3. Run an initial calibration scan with morfeus_scalar.py. Save the results in out.txt into a spreadsheet.
     
  4. Connect the filter in the RF chain, and then run a second scan with morfeus_scalar.py. Save the results into another column in the spreadsheet.

  5. Subtract the calibration scan results from the filtered results. Plot the resulting values using the spreadsheet software. This will show the response of the filter.

Download Example Spreadsheet (.xls) (.ods)

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