Category: RTL-SDR

Using an RTL-SDR and OpenCV To Create an EMI Heatmap of Circuit Boards

Over on YouTube and his blog user Charles Grassin has uploaded a short video and blog post showing how he's using an RTL-SDR EMI (electromagnetic interference) probe and OpenCV to create a visual EMI heatmap.

Earlier this month we posted about Dmitris' experiments in which he was able to create a home made EMI/EMC probe out of a loop of semi-rigid coax and an RTL-SDR V3. This type of probe is useful for determining what components or areas on a circuit board are emitting electromagnetic interference. EMI testing for PCBs may be critical for passing compliance tests.

Charles' project takes the RTL-SDR EMI probe idea a step further by combining it with OpenCV. OpenCV is an open source library of code for computer vision applications. With the EMI data generated by the RTL-SDR EMI probe, and a camera pointed at a PCB, Charles is able to overlay a heatmap on top of the visual image which reveals the EMI hot spots on a PCB.

The video below shows the EMI heatmap of an Arduino PCB being mapped out. His blog post shows some other examples like a keyboard and a hairpin RF filter. The code he's created is open source and available on his EMI_Mapper GitHub page.

EMI mapping (OpenCV and RTL-SDR)

KerberosSDR Batch One End of Stock, Batch Two Preorders Available

If you weren't aware, KerberosSDR is our recently released 4x Coherent RTL-SDR which can be used for tasks such as direction finding and passive radar. KerberosSDR was successfully crowdfunded over on Indiegogo, and we have recently completed shipments to all backers. Currently there is only about 20 units of the batch one production left in stock.

We are currently offering discounted preorders for batch two units on Indiegogo which we expect will be ready to ship in July or hopefully earlier. If you are interested, please order soon to avoid missing out as the price will be raised again once we are shipping. Batch two will be the same as batch one except for some minor changes. For example we have decided to convert the microUSB port into a USB-C port as we have found that there are many very poor quality microUSB cables on the market which could cause issues for users. USB-C cables are generally of a higher quality.

More information about KerberosSDR is available on the Indiegogo page.

KerberosSDR Updates

Since our last post on this blog about KerberosSDR we have made some enhancements to the software.

  • The KerberosSDR code is now fast enough to run at 1-2 Hz update rates for direction finding and passive radar on a Raspberry Pi 3 B+.
  • There is now a web interface, so the KerberosSDR can be controlled via a WiFi hotspot and internet browser. Useful for use on the Pi 3 and Tinkerboard.

For future updates we are currently working on several new features:

  • Filters to remove low confidence DoA results on the Android app.
  • A secondary heatmap type display on the Android app based on signal strength, for two direction finding indications.
  • Methods to determine the center of multiple bearing intersection points.
  • Further enhancements to processing speed, possible improved results from processing gain and possible better accuracy from improved DoA algorithms.

Within the next few weeks we will also release full tutorial videos that will show how to set up and use the KerberosSDR for direction finding and passive radar with a Raspberry Pi 3 or Tinkerboard. If you prefer a text based explanation we already have a guide up at rtl-sdr.com/ksdr.

Below is an image that demonstrates the KerberosSDR direction finding Android app. A user of KerberosSDR has also submitted two of his own screenshots that show that he was able to determine the location of a GSM transmitter with a linear antenna array.

KerberosSDR Direction Finding Results
KerberosSDR Direction Finding Results. Multiple data points collected during a drive, with bearings pointing towards the TX tower (red marker). Circular array of whip antennas used at freq. 858 MHz.

Scanner School Podcast Talks SDR Topics with Signals Everywhere Host

Recently Scanner School released episode 70 of their podcast, and on this episode they talk about various SDR topics with Corrosive from the Signals Everywhere YouTube channel. If you follow out blog, you'll know that Corrosive is a YouTuber that is consistently putting out high quality YouTube videos on a range of SDR and other radio related topics.

Scanner School is an online workshop that aims to help you get setup with an RTL-SDR based DMR/NXDN/P25 trunking system in four classes. They also have a weekly podcast. The description of this weeks podcast with Corrosive reads:

Corrosive has been working on his YouTube channel for about 4 years, and has a ton of videos on the SDR topic. If there is something that I am looking a trying when it comes to SDR, the first place I look is on Corrosive's channel.

Today we talk about some advanced SDR topics, both for receiving and transmitting.

While we talk about the more advanced topics of SDR today, I know we all have to start somewhere. If you are looking for online training to help you get started with SDR, check out our new Intro to SDR Workshop. This course will guide you though purchasing an excellent and affordable SDR to get started with.

Additionally, we will turn this SDR into a DMR, P25, and NXDN trunked receiver that can do more than your expensive scanner.


HackSpace Magazine Discusses SatNOGS, Cubesats and More

HackSpace is a monthly magazine dedicated to modern maker projects. This month issue 18 was released and it focuses on space based projects. The HackSpace Magazine is available for free online in PDF form, and physical copies can also be purchased.  There are several interesting articles but one in particular shows us how to set up a SatNOGS ground station with a Raspberry Pi 3, RTL-SDR and a satellite antenna such as a turnstile. 

A problem with low cost satellites like cubesats is that it is difficult to monitor them as data can only be collected when they are passing over a ground station. So in areas with no ground stations data is simply lost. SatNOGS is an open source project that aims to make it easy for volunteers to build and run RF ground stations that automatically monitor satellite data, and upload that data to the internet for public access. SatNOGS ground stations typically use RTL-SDR dongles as the radio.

A related article in the magazine also discusses cubesats, giving an overview of some previous cubesat launches and what sort of payloads are available. A third article under the space topic discusses the Libre Space Foundation which is the team behind the SatNOGS and various other space based projects that aim to democratize space. Readers may also be interested in the articles showing how to build an ISS countdown timer and how to build a Slim Jim antenna.

HackSpace Magazine SatNOGS Article
HackSpace Magazine SatNOGS Article (Excerpt)

Testing a $2 USB Powered LNA with RTL-SDR

Over on his blog '19max63' has posted about his tests with a $2 Aliexpress low noise amplifier (LNA) and his RTL-SDR. The LNA is advertised as for boosting HDTV signals, but 19max63 has found that it does a decent job on other frequencies too. It can be found on Aliexpress for less than $2 including free shipping, by searching for "TV Antenna signal amplifier". One example listing is this one.

An LNA is useful to help lower the noise figure of a radio system which results in higher SNR values (especially at the UHF and higher bands), and can be used to overcome losses in the signal chain from components like coax cables and connectors. However, an LNA will not always help and when combined with strong in or out of band signals will make reception worse by causing overload and intermodulation products. Better quality LNAs have a low noise figure, and are able to handle stronger signals and not overload so easily.

Ultra Cheap $2 LNA
Ultra Cheap $2 LNA

Upon opening the cover, 19max63 found that the cheap LNA consists of a BFG425W transistor which should cover 40 MHz to 3 GHz, but may be band limited by the passive components. The BFG425W also has a max gain of 20dB at 2GHz and a noise figure of 0.8 dB at 900 MHz. 

In 19max63's tests, the LNA was able to improve his DAB radio (174 to 240 MHz) reception significantly, allowing him to receive several extra stations. His further tests also seem to show that it does a decent job at other frequencies from 137 MHz NOAA satellites to 1090 MHz ADS-B. Many of the comparison images do seem to show signs of overloading and intermodulation, but ADS-B in particular looks to be boosted quite nicely. So this looks like it might be a very cheap way to try and improve ADS-B reception.

Check out the his post for multiple SNR comparison images.

Cheap LNA PCB
Cheap $2 LNA PCB

Receiving and Decoding the NAVIC (Indian GPS) Satellites

NAVigation with Indian Constellation (NavIC) (previously known as IRNSS) is an Indian navigation system consisting of 7 satellites in geosynchronous and geostationary orbits above India. It is intended for both public and military use, with a public resolution of up to 20m, and military resolution of up to 1m. After a few set backs, the satellite constellation was completed in April 2018.

Over on his blog Radiojitter, Priyasloka has put up a post showing how he was able to receive and decode the IRNSS/NAVIC satellites. To do this he uses an RTL-SDR with a GNSS antenna connected, and a modified version of the MATLAB GPS code found in this previous post, and in SoftGNSS. His post first goes through how he was able to decode and receive GPS, then goes over the technical details of the NAVIC signal, and then shows some result screenshots where he was able to determine his location with both GPS and NAVIC.

Priyasloka writes that he hasn't uploaded the modified code yet, but he plans to do so soon.

NavIC positioning results received with an RTL-SDR
NavIC positioning results received with an RTL-SDR

Help Support RadioCapture – A Project that Records Entire Trunked Radio Systems and Provides Online Access to Audio

RadioCapture.com is a website run by Matt Mills that is capable of automatically capturing trunked radio communications from various agencies such as the emergency services and creating publicly accessible historical and live logs of the audio. This is a concept different to radio scanner streams, as all audio is logged and historical audio can be accessed easily at any time.

The system is based on SDR hardware such as the RTL-SDR. Currently Matt runs a receiver in Denver and captures Denver PD which can be listened to on the site without needing to log in. Once logged in (registration is free), other talkgroups available include various agencies in Colorado, New Jersey and Pennsylvania.

RadioCapture.com currently available Talkgroups being logged
RadioCapture.com: Currently available talkgroups being logged

Recently Matt has put a call out for people to help support the site via Patreon. He notes that RadioCapture is currently run as a hobby, but with monetary support he hopes to be able to expand the site into a business and have receivers listening and uploading worldwide. He writes:

Hey! Thanks for supporting the continued operation and development of Radiocapture.com. This is a hobby project I've been working on this since late 2011. I'd like to turn it into a real business with your help.

Radiocapture.com is a software defined radio system I built that captures entire trunked radio systems. It demodulates and captures every call on every channel of one, or many systems.

A single RadioCapture server can capture hundreds of simultaneous voice transmissions and a bunch of sites, additionally it's designed in such a way that it can run across multiple computers. My biggest RF site uses 3 machines to capture 19 P25 systems, and easily hits more than 100 active voice channels recordings simultaneously every day.

Matt has also noted that if the site is able to become self-sustaining via Patreon, he hopes to also be able to bring out a RadioCapture kit consisting of 10-16 RTL-SDR dongles, hubs and cables which would allow anyone to easily capture and upload almost all trunked communications from their area. He also notes that at the time of writing:

RadioCapture has 701790271 unique recordings of 503779875 unique transmissions (some calls get captured on multiple transmitters) from the 21 systems that have been captured

If you're interested in talking to Matt about the site, you can also join his Rocket.Chat room at radiocapture.chat.

RadioCapture logged audio
RadioCapture playing logged audio

SignalsEverywhere Podcast EP2: Common SDR Mistakes and How to Resolve Them

Corrosive from the SignalsEverywhere YouTube channel has recently released episode two of his new podcast. This episode is titled "Common SDR Mistakes and How to Resolve Them". In the podcast Corrosive discusses some tips like how to ensure that the gain on your SDR is set correctly, how to set the sample rate, how to optimize the waterfall display, and what antennas to use. Later he goes on to talk about our RTL-SDR Blog V3 dongles, and discusses some posts from our blog.