Software-defined radio (SDR) is a radio communication system where components that have been traditionally implemented in hardware (e.g. mixers, filters, amplifiers, modulators/demodulators, detectors, etc.) are instead implemented by means of software on a personal computer or embedded system.
Experimenting with software defined radio used to be expensive, but now it is cheap. Nowadays it is very cheap to start experimenting with SDR. Most receivers use a variable-frequency oscillator, mixer, and filter to tune the desired signal to a common intermediate frequency or baseband, where it is then sampled by the analog-to-digital converter. Cheapest wide receiving range well working device is to use suitable DVB-T receiver stick (10-20 Euros/Dollars) and suitable software (very many alternatives, for example SDRsharp and Gnu Radio).
My article Software defined radio with USB DVB-T stick started the long list of SDR related postings. The newest postings now are Filter measurements with RF noise source and Antenna measurements with RF noise source.
432 Comments
Tomi Engdahl says:
Extend SDR Transmit Range – LimeSDR – HackRF – Adalm Pluto Amplifier
https://qrznow.com/extend-sdr-transmit-range-limesdr-hackrf-adalm-pluto-amplifier/
Tomi Engdahl says:
https://hackaday.com/2020/09/01/tinysa-is-a-49-spectrum-analyzer/
Tomi Engdahl says:
https://hackaday.com/2020/09/02/flipper-zero-blasts-past-funding-goal-and-into-our-hearts/
Tomi Engdahl says:
3D Printed Radio | No Batteries
https://www.youtube.com/watch?v=KGhe3OrNIlI
new 3D printed AM radio! I was inspired by the diy crystal and foxhole radios of the early 1900′s, but I created my own design to be as simple as possible. I made a few animations to help assist in explaining how this mystifying device can work with so few parts. I hope you like it and thank you for watching!
Tomi Engdahl says:
https://hackaday.com/2020/09/05/comparing-shortwave-antennas-with-rtl-sdr-and-python/
Tomi Engdahl says:
https://hackaday.com/2020/09/06/recognizing-activities-using-radar/
Tomi Engdahl says:
Raspberry Pi SDR Cyberdeck
A portable, rugged, self-contained system to suit all your RF SIGINT needs in every environment.
https://hackaday.io/project/174301-raspberry-pi-sdr-cyberdeck
Tomi Engdahl says:
Tutorial For Setting Up Raspberry Pi For Ham Radio Use
https://hackaday.com/2020/09/08/tutorial-for-setting-up-raspberry-pi-for-ham-radio-use/
Tomi Engdahl says:
Taking a look at Gerät 32620
The machine that powered numerous Number Stations
https://blog.ardy.io/2020/8/geraet-32620/
Tomi Engdahl says:
TinySA: RF Analysis in Your Pocket
Add the tinySA to your toolkit for MF/HF/VHF/UHF testing in the field
https://www.hackster.io/news/tinysa-rf-analysis-in-your-pocket-5c041d3bc9d1
Tomi Engdahl says:
SDR Transmitting Gets The Power
https://hackaday.com/2020/08/29/sdr-transmitting-gets-the-power/
Most hobby-grade software defined radio setups don’t transmit. Of the few that do, most of them put out anemic levels around one milliwatt or so. If you want to do something outside of the lab, you’ll need an amplifier and that’s what [Tech Minds] shows how to do in a recent video.
The video covers LimeSDR, HackRF, and the Pluto SDR, although the amplifiers should work with any transmitter. The SPF5189Z module is quite cheap and covers 50 MHz to 4 GHz, amplifying everything you throw at it. The downside is that it will amplify everything you throw at it, even parts of the signal you don’t want, such as spurs and harmonics.
https://www.youtube.com/watch?v=yOkdg1lGfes&feature=emb_logo
Tomi Engdahl says:
Software Defined Radio Academy Goes Virtual
https://hackaday.com/2020/07/08/software-defined-radio-academy-goes-virtual/
Tomi Engdahl says:
Driving A PAL TV Over RF Thanks To PWM Harmonics
https://hackaday.com/2020/08/26/driving-a-pal-tv-over-rf-thanks-to-pwm-harmonics/
While most analog televisions come with composite video inputs on a yellow RCA jack, the feature is not universal. This problem was even more prevalent in the 1980s, and most home consoles got around the problem by instead feeding video to the television’s tuner with an RF modulator. [Manzel Seet] had just such a television which used the PAL standard. Wanting to display images from a microcontroller, he put together PAL-Streamer.
The aim of the project was to display images on an analog television with minimal investment in hardware over and above what [Manzel] already had on hand. To this end, the project was built using a STM32F411 Nucleo development board. Capable of running at clock speeds up to 100 MHz, there’s plenty of grunt to handle demanding tasks like outputting video signals to a TV.
https://hackaday.io/project/171977-pal-streamer
Tomi Engdahl says:
https://hackaday.com/2020/08/29/auxiliary-display-makes-ham-radio-field-operations-easier/
Tomi Engdahl says:
https://hackaday.com/2020/07/10/how-early-radio-receivers-worked/
Tomi Engdahl says:
WiFi Goes Open
https://hackaday.com/2020/05/29/wifi-goes-open/
For most people, adding WiFi to a project means grabbing something like an ESP8266 or an ESP32. But if you are developing your own design on an FPGA, that means adding another package. If you are targeting Linux, the OpenWifi project has a good start at providing WiFi in Verilog. There are examples for many development boards and advice for porting to your own target on GitHub.
The demo uses a Xilinx Zynq, so the Linux backend runs on the Arm processor that is on the same chip as the FPGA doing the software-defined radio. We’ll warn you that this project is not for the faint of heart. If you want to understand the code, you’ll have to dig into a lot of WiFi trivia.
https://github.com/open-sdr/openwifi
Tomi Engdahl says:
https://hackaday.com/2020/06/27/433-on-a-stick/
Tomi Engdahl says:
https://hackaday.com/2020/08/07/lightning-analysis-with-your-sdr/
Tomi Engdahl says:
https://hackaday.com/2020/07/28/trunking-police-scanning-with-sdrtrunk/
Tomi Engdahl says:
Virtual Software Defined Radio
https://hackaday.com/2020/08/07/virtual-software-defined-radio/
Tomi Engdahl says:
Stop Bad Laws Before They Start
https://hackaday.com/2020/07/25/stop-bad-laws-before-they-start/
With everything else going on this summer, you might be forgiven for not keeping abreast of new proposed regulatory frameworks, but if you’re interested in software-defined radio (SDR) or even reflashing your WiFi router, you should. Right now, there’s a proposal to essentially prevent you from flashing your own firmware/software to any product with a radio in it before the European Commission. This obviously matters to Europeans, but because manufacturers often build hardware to the strictest global requirements, it may impact everyone. What counts as radio equipment? Everything from WiFi routers to wearables, SDR dongles to shortwave radios.
The idea is to prevent rogue reconfigurable radios from talking over each other, and prevent consumers from bricking their routers and radios. Before SDR was the norm, and firmware was king, it was easy for regulators to test some hardware and make sure that it’s compliant, but now that anyone can re-flash firmware, how can they be sure that a radio is conformant? Prevent the user from running their own firmware, naturally. It’s pretty hard for Hackaday to get behind that approach.
https://ec.europa.eu/info/law/better-regulation/have-your-say/initiatives/2042-Application-of-Article-3-3-i-and-4-of-Directive-2014-53-EU-relating-to-Reconfigurable-Radio-Systems
Tomi Engdahl says:
Eavesdropping On Satellites For Fun And Profit
https://hackaday.com/2020/08/20/eavesdropping-on-satellites-for-fun-and-profit/
Tomi Engdahl says:
Reception of Radio Waves Below 22 kHz
https://www.eeweb.com/reception-of-radio-waves-below-22-khz/?utm_source=newsletter&utm_campaign=link&utm_medium=EEWebEngInsp-20200924
The band we are going to “listen to” is located in the frequency between 0 and 22 kHz. As it can be seen from the table below, these are very low frequencies, corresponding to the audio frequencies that can be heard by humans, but which also involve emissions of electromagnetic waves. If the generation of a signal at these frequencies is very simple, it is not so easy to build the tuned antennas, as the corresponding wavelength is equal to hundreds and thousands of kilometers. For example, a half-wave dipole tuned to a frequency of 1,500 Hz should have a range of about 50 km. It’s an impossible thing to happen. On these low frequencies, there are no satisfactory receivers on the market and the antennas must be prepared with great care. Our computer’s sound card behaves like a great receiver but must be connected to a suitable antenna. In addition to the sound card, a software is required for viewing, recording, and analyzing the received signal. The VLF band is a very small fraction of the entire radio spectrum. It certainly gives a lot of satisfaction, even using low-cost emergency vehicles. Animals and humans are probably also able to receive some signals of this type and our brains may be more sensitive to the ULF band.
Band Frequency
ELF 3 Hz to 30 Hz
SLF 30 Hz to 300 Hz
ULF 300 Hz to 3 kHz
VLF 3 kHz to 30 kHz
LF 30 kHz to 300 kHz
Listen or read?
In these low-frequency bands, the signals are not heard in loudspeakers or headphones, or rather, the emission of sounds could occur but it is not the main activity, as is normally the case on other frequencies. On the contrary, the various emissions “listen” by decoding and appropriately interpreting a spectrogram
Today, it is very easy to receive low-frequency radio signals and it is not necessary to have an expensive receiver. It is sufficient to have a personal computer equipped with a sound card and software to obtain an analysis of the observed band. In a spectrogram at these frequencies, all kinds of natural and human signals can be observed. The latter are always coded and digital, so their interpretation is often complicated. The 0- to 22-KHz band is still a mysterious and not enough explored field. In it, there are natural signals of any kind, both external and internal, generated by the earth and impulses also transmitted by human stations of various kinds. Unfortunately, the main frequency (50 Hz or 60 Hz) is very present in the spectrograms and often constitutes a small obstacle to overcome, due to the interference produced and the noises generated.
A minimal station
As mentioned above, building your own listening station in the VLF band is very simple. As shown in Figure 2, the main components to be used are the following:
An electrically quiet and peaceful place
An antenna
A preamplifier
An audio card
A personal computer
Software
Note that most of the work is done by the software. There are programs (even in freeware version) of excellent quality that also perform the function of amplifier and filter. For initial tests, the preamp and filter can be omitted.
In theory, given the low frequencies used and the related enormous wavelengths, an antenna with gigantic dimensions would be needed, even hundreds and thousands of kilometers. For the antenna, there are at least three solutions to follow (see Figure 3), according to the difficulty of the work to be performed, the results to be obtained, and the space available in the house:
A random wire antenna
A loop antenna
A ferrite antenna
An Earth dipole (to listen to the interior of the earth)
It is often useful to amplify the antenna signal, especially if the “listening” tests are done in the open countryside, where the signal is really “silent” and useful messages are actually received, without business or domestic interference to be attenuated. Audio suitable for use with a VLF antenna is easy to build. A gain of about +15 dB helps the signal come from the antenna in a slightly stronger way. Because the antenna impedance is very high, the construction of a FET preamplifier is recommended.
The electrical circuit of the amplifier works at low frequencies, the audio ones. Building it is not difficult and can be easily done.
The audio card
The sound card is the device that replaces the radio receiver, in the band that is between 0 and 22 kHz. The limit of 24 kHz depends on the bandwidth and sample rate of the PC sound card. If the card allows sampling rates up to 192,000 samples per second, signals up to 96 kHz can be observed.
The software
The task of the software is to record the signals, to provide a representation on the monitor and a recording on the hard disk. There are many programs dedicated to this listening activity, but those used for the article (see Figure 8) are the following:
HDSDR
WASP
SoX
In short, HDSDR is a freeware (SDR) program for Microsoft Windows. Its typical applications are radio listening, SWL, radio astronomy, and spectrum analysis. WASP is a free program for recording, viewing, and analyzing audio tracks. It is also possible to view spectrograms with it. SoX reads and writes audio files in the most popular formats and can apply effects. All features are available using the SoX command only. It is a very powerful command line audio processing tool, particularly suitable for making quick and easy edits and for batch processing. It allows viewing spectrograms in very high resolution.
Conclusion
The observation of spectrograms in the VLF band is certainly a very fascinating and mysterious activity, which will keep you stuck on your PC even at night, at least in the first days of activity. Experience improves one’s sensitivity in recognizing various electrical and natural signals. Many signals travel in this extremely low band and demonstrate how ground waves are capable of carrying messages over long distances.
Tomi Engdahl says:
Make a wideband antenna matching transformer
https://www.onetransistor.eu/2015/10/wideband-antenna-matching-transformer.html
Tomi Engdahl says:
KiwiSDR Vs RaspberrySDR — A Tale Of Two SDRs
https://hackaday.com/2020/09/30/kiwisdr-vs-raspberrysdr-a-tale-of-two-sdrs/
Once you move away from the usual software defined radio (SDR) dongles, you have only a few choices unless you want to drop some serious cash. One common hobby-grade SDR is the KiwiSDR. This popular unit runs Linux and can receive up to 30 MHz. The platform uses a dedicated A/D converter, an FPGA, and BeagleBone computer. Success of course breeds imitators, and especially when you have an open source design like the Kiwi, you are going to find similar devices with possibly different end goals. That’s how the RaspberrySDR came to be. This is a very similar unit to the KiwiSDR but it uses a Raspberry Pi, along with a handful of other differences. What’s different? [KA7OEI] tells us in a recent blog post.
Other than the obvious difference of the computer and all that it entails, the RaspberrySDR has a higher speed A/D (125 MHz vs 66 MHz) and 16-bits of resolution instead of the Kiwi’s 14 bits. This combines to give the Raspberry a wider receive range (up to 60 MHz) and — in theory — better performance in terms of dynamic range and distortion.
Comparing the “KiwiSDR” and the “RaspberrySDR” software-defined receivers
https://ka7oei.blogspot.com/2020/09/comparing-kiwisdr-and-raspberrysdr.html
Tomi Engdahl says:
https://www.circuitstoday.com/tv-transmitter-circuit
Tomi Engdahl says:
Reverse engineering my cable modem and turning it into an SDR
https://stdw.github.io/cm-sdr/
got curious about an old cable modem sitting in my closet, a Motorola MB7220. Initially I was interested in what kind of hardware it had and if it was running Linux. Some quick searching brought me to a thread on a web forum where people were discussing the built in spectrum analyzer feature used for diagnostics. Someone mentioned that they could see spikes corresponding to FM radio stations. This sparked a thought: if a cable modem and a digital TV tuner dongle are fundamentally doing the same thing (receiving and demodulating QAM signals), could a modem be turned into an SDR (software-defined radio) a la RTL-SDR?
The device is running eCos on a MIPS processor which is part of a Broadcom BCM3383 SoC. It turns out there are actually two MIPS processors on this SoC although one of them is not used on this modem, explaining the other UART. On some devices, the second processor will run Linux for additional features.
Examination of the board reveals a single SPI flash chip which likely contains the bootloader, OS, and configuration
To actually read the chip, there is a fantastic tool called flashrom which supports an enormous number of chips. flashrom is present in the repos of many distributions including that of the Raspberry Pi OS (formerly known as Raspbian).
Although you get a full 15MHz since these are complex-valued samples, the usable range of the band pass filter is more like 7.5-8MHz with an assumed 15MHz sample rate which matches up.
At 15 million samples per second and each sample with occupying 8 bytes, less than a second of data can be stored in the approximately 100MB of free RAM.
Although dropping some data is bad some some applications, it can stream FM radio fairly seamlessly, although the audio has to be slowed down slightly so it is not consumed faster than it is being recieved. I have also been able to be recieved. I have also been able to pick up the 154MHz narrowband FM radio used by the local fire department.
Tomi Engdahl says:
https://hackaday.com/2020/10/10/the-cable-modem-to-sdr-transformation/
Tomi Engdahl says:
EASY-SDR GETS UPDATES
https://hackaday.com/2020/10/30/easy-sdr-gets-updates/
Back in 2018, we covered [Igor’s] Easy-SDR project that aimed to provide open hardware extensions for the chap RTL-SDR receivers.
https://hackaday.com/2018/11/09/all-the-goodies-you-need-for-your-rtl-sdr/
Tomi Engdahl says:
RF OSCILLATORS
http://mag.breadboard.pk/rf-oscillators/
Tomi Engdahl says:
Measurements on magnetic cores
https://www.qsl.net/in3otd/electronics/magnetics/magnetics.html
Sometimes one finds some magnetic core in the junkbox, at hamfests or dismantling electronic equipment and wonders if these could be useful for some projects.
Knowing the core material permeability and losses over frequency is of course the first step to understand of those cores can be useful for some RF applications or were intended for other applications.
Tomi Engdahl says:
This DIY DSP-based AM/FM/SW radio seems to be well ‘received’ by the community!
AM/FM/SW Radio Receiver – Si4730 / Si4735 © GPL3+
https://create.arduino.cc/projecthub/CesarSound/am-fm-sw-radio-receiver-si4730-si4735-79438f
DIY AM/FM/SW/ DSP radio receiver, using Arduino Uno/Nano and a color display TFT ST7735 1.8in.
Tomi Engdahl says:
This hands-on #review compares swept and real-time #SpectrumAnalyzers for #EMI debugging #PCB #TestAndMeasurement SIGLENT TECHNOLOGIES
https://buff.ly/2HY8R58
Review: Siglent SSA3075X-R real-time spectrum analyzer
https://www.edn.com/review-siglent-ssa3075x-r-real-time-spectrum-analyzer/?utm_content=buffer60232&utm_medium=social&utm_source=edn_facebook&utm_campaign=buffer
Digital circuitry can produce a wide range of harmonic frequencies and spectrum analyzers can show you this RF frequency spectrum (power or voltage), versus frequency. They are the one piece of gear that’s essential for EMC troubleshooting, but these instruments have traditionally been the most expensive item in anyone’s kit. However, several manufacturers are now making affordable quality instruments that are perfectly adequate for troubleshooting and pre-compliance work.
Both Rigol and Siglent Technologies released affordable swept spectrum analyzers several years ago and recently, both released real-time analyzers.
Swept or real time?
We now have a choice to make: there are basically two types of measurement acquisition in spectrum analyzers; swept and real time. Swept analyzers are very similar to classic oscilloscopes in that the frequency span is “swept” between the start and stop frequencies, then analyzed and displayed in a series of events (sweep – analyze/measure – display), so there is some deadtime between sweeps while the system is measuring, processing the data, and displaying the results.
This delay can miss some pulsating or intermittent frequency captures. Real-time acquisition, on the other hand, captures and displays the frequency information at such a rapid process that it appears as if the display is showing captured data in “real time.” This fast acquisition depends on extremely fast A/D conversion, simultaneous FFT processing, and powerful computer processors. Some of the higher-priced real time analyzers can generally capture impulsive RF events down to nearly 1 μs (with 100% probability of intercept (POI)) and are very useful for displaying intermittent interference or digital modulations and their characteristics.
As mentioned, a real-time spectrum analyzer has the ability to capture brief intermittent signals and are perfect for capturing modulated wireless or digital signals, as well as general EMI troubleshooting. For example, within the 2.4 GHz ISM band, you’ll see the entire spread spectrum Wi-Fi signal, as well as the frequency-hopped Bluetooth signals very clearly.
Tomi Engdahl says:
https://www.rtl-sdr.com/a-dual-aircraft-and-ship-tracking-system-with-rtl-sdr/
Tomi Engdahl says:
Transmit Radio Signals via Ethernet
This works by switching between 10Mbps and 100Mbps, which results in a change of the electromagnetic radiation that leaks from the devices. Switching to 100Mbps produces a signal at 125MHz, which is used to transmit morse code.
https://github.com/sq5bpf/etherify
https://lipkowski.com/etherify/
Tomi Engdahl says:
Review: Siglent SSA3075X-R real-time spectrum analyzer
https://www.edn.com/review-siglent-ssa3075x-r-real-time-spectrum-analyzer/
Tomi Engdahl says:
ETHERIFY – BRINGING THE ETHER BACK TO ETHERNET
https://lipkowski.com/etherify/
The transmission is implemented by a simple bash script, which sends the content of a short text file given as the argument, or “etherify demo” if none is given. The signal can be received as morse code around 125MHz, please use USB or CW mode in the receiver and use a narrow filter.
https://github.com/sq5bpf/etherify
Tomi Engdahl says:
PySDR: A Guide to SDR and DSP using Python
https://pysdr.org/
This textbook is designed for someone who is:
Interested in using SDRs to do cool stuff
Good with Python
Relatively new to DSP, wireless communications, and SDR
A visual learner, preferring animations over equations
Better at understanding equations after learning the concepts
Looking for concise explanations, not a 1,000 page textbook
Tomi Engdahl says:
Original mini software-defined radio turned out to be a little too mini for comfort, so its latest redesign concentrates on usability.
Circuit Salad’s Ray Ring Redesigns His Compact FV-1-Based Software-Defined Radio — to Make It Bigger
https://www.hackster.io/news/circuit-salad-s-ray-ring-redesigns-his-compact-fv-1-based-software-defined-radio-to-make-it-bigger-3d22accb67cd
Original mini software-defined radio turned out to be a little too mini for comfort, so its latest redesign concentrates on usability.
https://circuitsalad.com/2020/11/13/the-fv-1-based-sdr-revisited/
Tomi Engdahl says:
Ham Radio Needs To Embrace The Hacker Community Now More Than Ever
https://www.kj7nzl.net/blog/ham-radio-needs-to-embrace-the-hacker-community-now-more-than-ever/
Tomi Engdahl says:
New NPR-H Modem Upgrades F4HDK’s Original Design with On-Board Amps, Power Over Ethernet
Kuek’s redesign includes an on-board LNA and PA, additional SRAM, and an Ethernet port with integrated Power over Ethernet.
https://www.hackster.io/news/new-npr-h-modem-upgrades-f4hdk-s-original-design-with-on-board-amps-power-over-ethernet-3c10a94fe1a2
Tomi Engdahl says:
HackRF PortaPack Firmware Spoofs All The Things
https://hackaday.com/2020/11/28/hackrf-portapack-firmware-spoofs-all-the-things/
The HackRF is an exceptionally capable software defined radio (SDR) transceiver, but naturally you need to connect it to a computer to actually do anything with it. So the PortaPack was developed to turn it into a stand-alone device with the addition of a touchscreen LCD, a few buttons, and a headphone jack. With all the hardware in place, it’s just a matter of installing a firmware capable enough to do some proper RF hacking on the go.
Enter MAYHEM, an evolved fork of the original PortaPack firmware that the developers claim is the most up-to-date and feature packed version available. Without ever plugging into a computer, this firmware allows you to receive, decode, and re-transmit a dizzying number of wireless protocols. From firing off the seating pagers at a local restaurant to creating a fleet of phantom aircraft with spoofed ADS-B transponders, MAYHEM certainly seems like it lives up to the name.
https://github.com/eried/portapack-mayhem
Tomi Engdahl says:
Name That Unknown RF Signal With A Little FFT Magic
https://hackaday.com/2020/02/11/name-that-unknown-rf-signal-with-a-little-fft-magic/
Time was once that the amateur radio bands were an aurally predictable place. Spinning the dial up and down the bands, one heard familiar sounds – the staccato of Morse, the [Donald Duck] of sideband voice transmissions, and the occasional flute-like warble of radioteletype signals. Now, the ham bands are full of exotic signals encoding all manner of digital signals, each one with a unique sound and unique demodulation needs. What’s a ham to do?
Help is on the way. [José Carlos Rueda] has made progress toward automatically classifying unknown signals by modifying a Shazam-like app. Shazam is a popular smartphone app that listens to a few seconds of a song, creates an audio fingerprint of it, and searches a massive database of songs for a match. [Rueda] used a homebrew version of the app to search a SQL-lite database of audio fingerprints populated not with a playlist of popular music, but with samples from every known signal type in the Signal Identification Wiki.
http://jcrueda.com/?p=916
https://www.sigidwiki.com/wiki/Database
Tomi Engdahl says:
https://www.digikey.com/en/articles/how-and-why-to-use-pin-diodes-for-rf-switching
Tomi Engdahl says:
HAM RADIO NEEDS TO EMBRACE THE HACKER COMMUNITY NOW MORE THAN EVER
https://hackaday.com/2020/11/28/ham-radio-needs-to-embrace-the-hacker-community-now-more-than-ever/
Tomi Engdahl says:
#111 Texscan AL-60 70s Spectrum Analyzer 0-3 GHz Teardown
https://www.youtube.com/watch?v=6xr7mhMnj0s
Tomi Engdahl says:
https://www.electronics-tutorials.ws/amplifier/common-base-amplifier.html
Tomi Engdahl says:
Transmits AM radio on computers without radio transmitting hardware.
https://github.com/fulldecent/system-bus-radio
Tomi Engdahl says:
#129 MAX2870 LCD Signal Generator vs ADF4351 LCD Review Teardown
https://www.youtube.com/watch?v=DFtC7icVr-E
Tomi Engdahl says:
I Found & Eliminated My QRM / RFI (Radio Frequency Interference)!
https://m.youtube.com/watch?v=Pwbk8yP6SIkIt
This is the third in a series of videos following my efforts to track down a source of local QRM / Radio Interference. Following the build of a successful direction finding loop, in this video I build an RF sniffer probe and track down the source of QRM and finally eliminate it! The sniffer is for pointing to suspect items up close when perhaps the loop might be overwhelmed or non-directional if say inside a building.