Obtaining an Antenna Radiation Pattern with a Large Field, Android Device and RTL-SDR

An antenna's radiation pattern tells us how it radiates or receives electromagnetic energy in different directions, indicating the strength, directionality, and coverage area of its signals. These days, this is easy to simulate on a PC. However, getting real-world results can still be essential to ensure an antenna is constructed well. For commercial antennas, real-world testing is typically done in an RF anechoic chamber.

Over on Hackaday, Jenny List shows us an alternative method for measuring an antenna's radiation pattern: setting up an antenna in a large field and taking RF measurements at various locations around it using an RTL-SDR.

In the post, List tests an HB9CV two-element 144MHz Yagi antenna. As expected, the resulting polar plot from the measurements indicates that the HB9CV is a directional antenna.

We've seen a similar setup in the past, as shown in this post, where a NanoVNA was used to measure the antenna power.

Antenna Field Test Setup
Antenna Field Test Setup

 

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AI Cloud Detection for GOES Weather Satellite Images on a Raspberry Pi

Over on his blog account at Hackser.io Justin Lutz has uploaded an article describing how he uses AI object detection to automatically detect clouds on weather satellite images that he's downloaded from GOES satellites via an RTL-SDR.

Lutz's blog post first describes and shows his RTL-SDR GOES reception setup. Then, it explains how he used Edge Impulse on his Raspberry Pi 4 to create an AI model that automatically detects the clouds in the image.

The process begins by importing 100 images into Edge Impulse, manually labelling the clouds in each image, training the model, and testing it. The result was an average detection accuracy of 90%.

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SDR Television: DATV TX and RX Software for the PlutoSDR

Recently, Simon Brown (G4ELI), best known for being the author of the popular SDR-Console software, has released a new program called "SDR Television (Beta 2)". SDR Television is a program designed for transmitting and receiving Digital Amateur TV (DATV) signals.

At the moment, the software supports DATV on the QO-100 satellite, but in the future, further terrestrial DATV support has been promised. The software is designed to be used with a PlutoSDR (or PlutoSDR clone or spinoff), but also supports Airspy or SDRplay for receive only.

Over on YouTube, Tech Minds has also posted a great video demonstrating the software's setup and use.

SDR TELEVISION V1.0 - Game Changing DATV Software From G4ELI!

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The Open-Weather Project’s Year Of Weather: June 15 NOAA EOL Nowcast Scheduled

Dr. Sasha Engelmann and Sophie Dyer, the team behind the Open-Weather project have recently announced a NOAA end-of-life nowcast to be recorded on June 15 2025. An open weather nowcast is a collaborative effort with users all around the world sending in weather satellite images that they have received locally with their home SDR setups.

NOAA satellite weather image APT transmissions have long been a staple of RTL-SDR hobbyists as they are among the easiest and cheapest satellite transmissions to receive. A simple V-dipole, RTL-SDR, and a computer are all that is required.

Sadly, it was recently announced that the NOAA satellites will be classified as end-of-life (EOL) on June 16 2025. However, the good news is that APT and HRPT data transmissions are expected to continue as usual. The end-of-life status indicates that NOAA will cease its own collection of data from these satellites and, hence, will no longer be distributing the datasets online. It also means that the satellites should no longer be used for mission-critical or scientific purposes and that no attempt will be made to fix a failing satellite.

These satellites have been operating well past their operational life, and given their advanced age, failure could come at any time. So the Open-Weather nowcast on June 15 2025 remains a nice way to honor their service to humanity.

You can see the last Year of Weather map created by the Open-Weather team and contributors here https://open-weather.community/yow/map/

The recent newsletter from the Open-Weather team explains how to participate in the June 15 nowcast.

OpenWeather Current Screenshot
OpenWeather Current Screenshot
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Saveitforparts: Taking Videos of Geostationary TV Satellites via a DIY Radio Telescope

In a recent video on the saveitforparts channel Gabe shows how he used a DIY radio telescope to take a video of geosynchronous TV satellites. The system works by using a motorized dish to scan the sky at Ku-band frequencies. An SDR is used to receive the signal strength at each dish position, and this data is used to create a heatmap image.

Each scan takes an hour to scan the sky, but by running a scan every hour, Gabe is able to create a video of the geosynchronous satellites wobbling. While still mostly fixed at one position in the sky, unlike geostationary satellites, geosynchronous satellites can appear to move in a figure-eight pattern from the ground, and this wobbly movement is apparent from Gabe's video.

The video also shows the sun passing by every 24 hours as the sun emits some RF energy in the Ku-band, as well as brief blips from Starlink satellites. The video also shows the effect of rain fade, as Gabe shows how the heatmap power was attenuated during poor weather.

Videos Of Satellites In Space Made With DIY Radio Telescope

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New Khanfar Software: RTL-SDR CFAR Mask Analyzer

Recently, software developer M. Khanfar has been releasing a lot of new SDR and RTL-SDR compatible software, which you can see by searching for Khanfar on our blog.

Recently M. Khanfar has released a new program called "Khanfar RTL-SDR CFAR - Mask Analyzer" which is software designed for RF signal detection and analysis. Khanfar writes:

This powerful tool combines advanced Constant False Alarm Rate (CFAR) algorithms with innovative  Frequency Mask Trigger (FMT) techniques to provide reliable signal detection even in challenging RF environments.

CFAR (Constant False Alarm Rate) is an advanced adaptive threshold technique developed originally for radar systems but extremely valuable for any signal detection application.

The Frequency Mask Trigger (FMT) functionality allows you to define signal-free areas in the spectrum where you expect no signals or want to ignore existing signals. The software automatically adapts to these masks, preventing false detections in known signal areas while maintaining high sensitivity in areas of interest.

What You'll Learn:
How CFAR adapts to changing noise environments
Impact of different algorithm parameters
Mask creation and application techniques
Optimal settings for different signal types

Perfect For:
Students learning signal processing
Radar enthusiasts and researchers
SDR hobbyists exploring advanced features
Engineers developing detection systems

The Khanfar RTL-SDR CFAR - Mask Analyzer brings many features traditionally found only in expensive commercial spectrum analyzers and radar systems to the affordable RTL-SDR platform and provides an incredible value for education, hobbyists, and even many professional applications.
The software was also soon after updated to support Airspy devices, and add Telegram integration. The Telegram integration allows users to set up remote monitoring, and have alerts and data delivered directly to your mobile device via the Telegram messenger chat software.

As mentioned in previous posts, antivirus software can flag M. Khanfar's software as suspicious. We suspect these are false positive results due to the PyInstaller system used to create the exe, but please take your own precautions just in case.

Khanfar RTL-SDR CFAR - Mask Analyzer

 
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ESP32-Div: An ESP32 Based Swiss Army Knife for Wireless Networks

On his blog, Cifer has posted about a new device that he's created called "ESp32-Div." ESP32-Div is a multi-featured wireless analysis device for WiFi, Bluetooth, 2.4 GHz, and sub-GHz signals. While ESP32-Div is not based on SDR technology, it is still an interesting device for wireless hackers to discuss.

ESP32-Div can monitor WiFi packets, spam fake WiFi access points, scan for deauth attacks, and scan nearby WiFi networks. For Bluetooth, it can jam, scan, spoof, and cause unintended behaviours on Apple devices via spoofing the AirDrop function. It can also be used as a general 2.4 GHz scanner and jammer. Finally, it can perform replay attacks and jam signals for sub-GHz signals.

The device consists of a custom PCB with an ESP32 and a built-in battery pack. A piggybacking shield adds 3x NRF24 modules for the 2.4 GHz features and a CC1101 module for the sub-GHz features.

Obviously, functions like jamming and spoofing are highly illegal in most countries, but it is interesting to see the capabilities available to anyone with these cheap chips and the right software.

ESP32-DIV: Your Swiss Army Knife for Wireless Networks

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RTL-SDR Provides Vital Information during Portugal & Spain Blackout

Over on LinkedIn Khalil A. has uploaded a short post highlighting how critical monitoring radio communications was during the mass power outage in Spain. This week Spain and Portugal experienced country wide blackouts, leaving more than 55 million people without power for more than half a day.

During the blackout, news was difficult to obtain as mobile services and internet connections failed. Khalil used a charged laptop and an RTL-SDR to monitor FM, AM, amateur, and emergency services, providing up-to-date information to his neighbourhood.

RTL-SDR provides news during Spain and Portugal blackouts
RTL-SDR provides news during Spain and Portugal blackouts.
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