A Video on Optimizing VLF Loop Antennas

VLF (Very Low Frequency) refers to signals in the 3–30 kHz range. Software-defined radios like the SDRplay RSPdx can pick up these signals with an appropriate antenna.

Over on YouTube, @electronics.unmessed has uploaded a video showing how you can build a high-performing VLF loop using a single loop of wire and a balun. The one-turn design results in a naturally low impedance at low frequencies. A balun is then added to step up the impedance, resulting in impedance compatibility with an SDR.

The video explains the concepts behind VLF loops using an equivalent circuit model and shows how conductor thickness offers little benefit above 10 kHz (though wide sheet conductors can add ~3 dB), larger loops scale with area but 2 m is a good indoor compromise, extra turns help small loops but underperform a single turn with a proper transformer, and alternative ferrite mixes give little improvement over standard choke cores. Ultimately, it is concluded that a one-turn loop with a well-chosen balun is one of the most effective designs.

If you're interested in similar content, there are also several other interesting videos on the @electronics.unmessed channel about VLF antennas, mag loop antennas, SDR reception, and more.

VLF Loop - What really Matters? (EP172)

Reverse Engineering the RF Communications on a 27 MHz RC Toy with an RTL-SDR and GNU Radio

On his blog, Jacob has recently uploaded an interesting post showing how he used an RTL-SDR to reverse-engineer the 27 MHz RF communications protocol used by his kids' RC toy truck.

To reverse engineer the protocol, Jacob used GNU Radio to visualize and demodulate the signal. He discovered that it was modulated via Amplitude Shift Keying (ASK), and viewing the waveform in a time-domain plot confirmed the on-off nature of the signal. Next, using symbol sync and thresholding blocks, he generated a bit pattern, which was then processed using Python.

Reverse Engineering the RC Toy Truck 27 MHz Signal
Reverse Engineering the RC Toy Truck 27 MHz Signal

Decoding ADS-C with a Cheap Aliexpress LNB and SDRplay RSP1B

Thank you to Nagy István for sharing with us his setup for decoding ADS-C with a 180cm prime focus dish, a cheap Aliexpress LNB, an Aliexpress bias tee, and an SDRplay RSP1B.

István receives the ADS-C signal from the Inmarsat 4A-F4 satellite, which he can see from his home in Hungary. 

István also notes the following information about the Chinese LNB:

This LNB original for DVB reception, but it works on Inmarsat reception, 3.6Ghz where ADS-C signals are, without any modification... But sometimes you need correcting frequency because of LNB oscillator drifting. I don't use dielectric plate, I don't have any material for this, at the moment.

Compared to ADS-B, which continuously broadcasts an aircraft’s GPS position and velocity to any ground station or nearby aircraft, ADS-C instead sends position reports via satellite, and is especially used over oceans and remote areas without ADS-B ground receivers.

However, ADS-C is relatively complex for hobbyists to receive due to the need for a large satellite dish and LNB to convert the 3.6 GHz frequency down to a frequency receivable by most SDRs. However, fortunately, as István shows, the LNB can be obtained cheaply these days.

Inmarsat ADS-C decoding with Jaero and Virtual Radar

ADS-C Being Received with an 1.8m dish, cheap Aliexpress LNB and SDRplay RSP1B.
ADS-C Being Received with an 1.8m dish, cheap Aliexpress LNB and SDRplay RSP1B.

rtl_tcp_echo: Record and Replay IQ Streams with a Transparent rtl_tcp Proxy

Thank you to Sarah Rose Giddings for submitting news about the release of one of her latest software programs called "rtl_tcp_echo". This “man-in-the-middle” application enables you to simultaneously monitor and record signals of interest, then replay the captured IQ data at a later time using software compatible with rtl_tcp.

The software is compatible with Linux, and Sarah notes that a Windows build will be available soon.

RTL_TCP_ECHO is a Go application that acts as a proxy between an rtl_tcp server and its client. It transparently passes control commands (such as frequency, gain, and sample rate), forwards IQ data, and records the IQ stream to a file. Later, you can run the application in playback mode, serving the recorded IQ data as a fake rtl_tcp server—allowing SDR software to connect and replay the IQ stream.

Features

  • Proxy Mode:
    Forwards all rtl_tcp commands (including frequency and gain) and IQ data between client and server. Simultaneously records IQ data to a file.

  • Playback Mode:
    Serves a previously recorded IQ file as an rtl_tcp-compatible server for SDR software to connect and decode.

  • Transparent Command Handling:
    All client commands (frequency, gain, sample rate, etc.) are passed through with optional logging.

  • Simple Configuration:
    Easily specify listen/forward addresses and recording/playback file paths via command-line flags.
rtl_tcp_echo usage
rtl_tcp_echo usage

An Introduction to SDR’s and GNU Radio using an RTL-SDR

Thank you to Paul Maine for submitting his latest YouTube video titled "Introduction to SDRs and GNU Radio Using an RTL-SDR". The video introduces the RTL-SDR and GNU Radio, and then proceeds to demonstrate how to build a simple FM receiver using GNU Radio. Paul goes on to explain some further concepts, such as sampling, aliasing, interpolation, decimation, upsampling, and finally shows a few more example receivers built in GNU Radio.

E18 Introuction to SDR's and GNU Radio Using an RTL-SDR

EU Ham Radio Shops Suspend Shipments to the United States

With the recent changes to US import policy, many shops in the EU, including ham radio shops, have begun suspending shipments to the United States. This is the result of both a widespread suspension of shipments to the US by most EU mail carriers and the ongoing unpredictability of the situation.

One French reseller of our products has written in to our blog, and wanted to explain the reason for their decision to suspend shipments to the US. We believe that other ham radio shops in the EU may also be in a similar position.

To our US Amateur Radio Clients and Community

Because of the recent 15% tariff increase on products imported from the European Union, the suspension of several carrier services to the US, and the growing complexity of the US import system, our online shop Passion-Radio.com must suspend all shipments to the United States until further notice.

In particular, La Poste, the French national postal operator, suspended parcel shipments to the United States as of August 25, 2025 (1), removing one of the main EU–US postal channels. At the same time, UPS announced that starting September 8, 2025, an additional international processing fee will apply to all import shipments, regardless of origin.

There has also been some misunderstanding regarding customs procedures. When parcels arrive in the United States, the buyer must settle not only the 15% customs duty, but also the service fee charged by the carrier for filing customs declarations and advancing duties to US Customs. These charges are billed locally at delivery and remain outside the seller’s control. Import duties and tariffs are always the responsibility of the buyer, not the seller.

"Unfortunately, with constant changes in tariffs, rates, and carrier processes, we cannot guarantee fair, efficient, and transparent shipping conditions," said David, F1JXQ, Director of Passion Radio. "Our goal is to resume shipments to the US as soon as a reliable and cost-effective solution is available for everyone."

Meanwhile, our collaboration with five US-based suppliers continues without disruption, as the European Union has not imposed any retaliatory tariffs or reciprocal 15% import duties on products arriving from the United States.

Updates will be communicated through our shop: https://www.passion-radio.com/store/hamradio-us-tariff-43 and our social channels.

To all our US friends on the bands: we thank you for your understanding and support, and we look forward to resuming deliveries as soon as possible.

They go on to explain an example:

Practical tariffs impact on an item €50

Before tariffs (without 15%, rate €1 = $1.12 April 2025 rate)

Conversion: €50 × 1.12= $56.00*

Total payable ≈ $56.00

After tariffs (with 15%, rate €1 = $1.16 August 2025 rate)

Conversion: €50 × 1.16 = $58.00*

Customs duty 15%: $58.00 × 0.15 = $8.70

Carrier fees (on average, import processing): $15.00

Total payable ≈ 58.00 + 8.70 + 15.00 = $81.70

Total surcharge ≈ +$25.70 (~+45.89% increase compared to $56.00, before tariff tax)

* Not calculated, fees that may apply when converting Euro € <> US $.

FAQ

• Q1: Who pays import duties and tariffs when ordering from Europe?

By law, the US buyer must pay all customs duties, tariffs, and fees when importing goods from Europe. These charges are not paid by the seller.

• Q2: Why do carriers charge extra fees?

Carriers like UPS, FedEx, or DHL must submit customs declarations and advance duties to US Customs. For this, they bill a brokerage or processing fee directly to the buyer.

Sources :

(1) https://www.lemonde.fr/economie/article/2025/08/22/la-poste-suspend-l-envoi-de-colis-vers-les-etats-unis_6633516_3234.html

WOW@Home: A Global Network of RTL-SDR Based Radio Telescopes Looking for Alien Technosignatures

The Wow! signal is a famous, strong, and unexplained radio signal detected in 1977 by the Big Ear radio telescope in Ohio, lasting 72 seconds and appearing to originate from the constellation Sagittarius. Its origin remains unknown, with some speculating that it could be an extraterrestrial technosignature. Upon reviewing the signal data, Astronomer Jerry R. Ehman discovered the powerful signal burst in the readout and wrote a large "Wow!" next to it, unintentionally coining the name.

Wow@Home is a new project that aims to coordinate a network of small radio telescopes globally, in the hopes of increasing our chances of detecting interesting astrophysical and technosignature events, such as the Wow! event.

A network of small radio telescopes offers several distinct advantages compared to large professional observatories. These systems are low-cost and can operate autonomously around the clock, making them ideal for continuous monitoring of transient events or long-duration signals that professional telescopes cannot commit to observing full-time.

Their geographic distribution enables global sky coverage and coordinated observations across different time zones, which is especially valuable for validating repeating or time-variable signals. Coincidence detection across multiple stations helps reject local radio frequency interference (RFI), increasing confidence in true astrophysical or technosignature transient events.

These networks are also highly scalable, resilient to single-point failures, and capable of rapid response to external alerts. Furthermore, they are cost-effective, engaging, and accessible, ideal for education, citizen science, and expanding participation in radio astronomy.

However, these systems also come with notable limitations when compared to professional telescopes. They have significantly lower sensitivity, limiting their ability to detect faint or distant sources. Their angular resolution is poor due to smaller dish sizes and wide beamwidths, making precise source localization difficult.

Calibration can be inconsistent across stations, and frequency stability or dynamic range may not match the performance of professional-grade equipment. Additionally, without standardized equipment and protocols, data quality and interoperability can vary across the network.

Despite these constraints, when thoughtfully coordinated, such networks can provide valuable complementary observations to professional facilities.

The team note that the Wow! signal was strong enough that it could have been detected by a small home radio telescope. They go on to make the case that we could be missing out on detecting many compelling signals simply because radio telescopes aren't watching every part of the sky simultaneously. 

The project will monitor the Hydrogen Line frequency for interesting signals. Currently, the team is using a WiFi grid dish and an external LNA as the radio telescope hardware, but they also aim to evaluate our Discovery Dish with H-Line feed.

Wow@Home Typical Radio Telescope Hardware
Wow@Home Typical Radio Telescope Hardware

WHY2025 Conference: Passive and Active RADAR using Software Defined Radio

Videos from the WHY2025 (What Hackers Yearn) have recently been uploaded to YouTube, and there is one interesting talk by Jean-Michel Friedt titled "Passive and active RADAR using Software Defined Radio". 

RAdio-frequency Detection And Ranging (RADAR) aims at using electromagnetic signals for detecting target location and motion. We demonstrate in this talk various RADAR architectures using dual-channel coherent Software Defined Radio (SDR) receivers and the associated signal processing techniques relying heavily on cross-correlations. Embedded systems are tackled, with a Raspberry Pi providing enough computational power for recording and post-processing.

RAdio-frequency Detection And Ranging (RADAR) aims at using electromagnetic signals for detecting target location and motion. Being constantly illuminated with electromagnetic smog, we can benefit from existing radiofrequency emitters meeting RADAR requirements -- strong power and wide bandwidth -- for passive RADAR measurements where no active emitter is needed, using only coherent passive dual-channel Software Defined Radio (SDR) receivers for passive recording of existing signals. If existing signals are unsuitable, we can use the same principle with non-cooperative emitters such as a Wi-Fi dongle in an active RADAR setup.

All processing flowcharts are implemented using GNU Radio for real time acquisition, and GNU/Octave or Python for post-processing: generic principles will be demonstrated, applicable to all sorts of receiver hardware. We will conclude with Synthetic Aperture RADAR (SAR) where antenna motion is used to simulate wide aperture receiving antennas, adding azimuth resolution to range resolution.

Supporting documents are found a https://github.com/jmfriedt/SDR-GB-SAR or https://github.com/jmfriedt/passive_radar orhttps://github.com/jmfriedt/sentinel1_pbr

WHY 2025 - Passive and active RADAR using Software Defined Radio