Tagged: airspy

Testing Airspy’s New WebSpy Web SDR Interface with an RTL-SDR

A couple of weeks ago we posted about "WebSpy", a new web client for Airspy software defined radios. Developer @lambdaprog, (aka Youssef Touil) has kindly provided us with an early beta of the server to test.

WebSpy is built into SpyServer, and SpyServer is an existing program that streams data from Airspy and RTL-SDR devices directly to SDR#. This new beta SpyServer now incorporates WebSpy into it, so once SpyServer is running on the server, all you need to do is run the binary and browse to https://SERVER_IP_ADDR:5555 in a browser, and the WebSpy interface will show.

As SpyServer supports RTL-SDR dongles, WebSpy also works as intended with RTL-SDRs. So in our test, we used a remote RTL-SDR connected to a networked Pi 5 and started up WebSpy. As the default includes self-signed certificates, you will get an unsecured warning from your browser, but this is safe to ignore. If you were to share your WebSpy publicly, you would want to generate your own certificates. Youssef recommended using acme.sh for that.

Clicking the power icon in the web interface starts the SDR connection, and then you can tune to frequencies using the top tuning interface like you would with SDR#. Audio is extremely clear, as if you were running the SDR directly. As Youssef explained in our earlier post, WebSpy uses some proprietary IQ compressors that preserve spurious-free dynamic range, and it does all the IQ decoding directly in the browser to avoid audio codec compression artifacts.

With an Airspy and RTL-SDR receiving a narrowband 12.5 kHz voice channel, we got about 25 kb/s network usage. Reducing the channel size to 2.4 kHz LSB reduces the usage to around 13 kB/s. A wideband FM signal at 200 kHz uses about 240 kB/s. Of course, expanding the channel size to the max 2.4 MHz of the RTL-SDR results in a much higher network bandwidth of 1.2 MB/s, but there are not many situations that would require that.

We tested in Chrome, Edge, and Firefox, and all browsers worked fine. In terms of CPU usage, it barely touched 10% on any core with a single user. Youssef mentioned that a single Pi 5 should be able to serve up to 40 simultaneous sessions for WFM users, and hundreds for SSB/AM users (and we suspect NFM too).

WebSpy CPU Usage
WebSpy CPU Usage

The implementation of WebSpy is still pretty bare in this beta. Most of the features present in SDR# are not there, but Youssef mentioned that these are being worked on, and plugin support may even be added in the future. You also can't tune individual frequency digits with the mouse wheel like you can in SDR#, and there are no squelch or bias-tee controls.  But as this is still in development, we expect more features and tweaks in the future. 

WebSpy Running an RTL-SDR
WebSpy Running an RTL-SDR
WebSpy Running an Airspy
WebSpy Running an Airspy

CellScope: LTE Sniffing on Windows

Over on YouTube, Sarah from the SignalsEverywhere YouTube channel has uploaded a new video showing a new open-source program she's developed called CellScope, which is used for LTE sniffing. She notes that CellScope is essentially LTE Sniffer, but ported for Windows. CellScope needs a wideband SDR, and it currently supports LibreSDR B210 Clone, HackRF and the Airspy R2/Mini

LTE (aka 4G) is a modern mobile wireless standard used by cellphones for data. While it is encrypted, there is still some data transmitted in the clear, such as the devices connected to the cell site and how much data they are pulling down, if there is an active call on the cell site, and of course the data activity can be useful to monitor too. 

In the video Sarah shows CellScope in action, demonstrating it detecting a call from her phone and visualizing the data transfer activity from her device when pulling down data.

CellScope is open-source and available on GitHub. If you don't want to compile it yourself, the Windows executable can be purchased from her site for a minimum $0.00 donation.

CellScope: LTE Sniffing on Windows

Airspy WebSpy: A High Performance Web UI Client for Airspy SDRs

Over on X @lambdaprog, (aka Youssef Touil), the developer of SDR#, has been teasing development of a new web client called "WebSpy" for Airspy software-defined radios. The web client allows users to tune in to a remote Airspy SDR via a web browser interface that mimics the SDR# Windows software. Before WebSpy, it has only been possible to access Airspy devices remotely via the SpyServer server software and the SDR# Windows application.

While the software is still in development and not yet available for download, you can access a demo version (HF server) (Broadcast FM server) that Youssef has currently set up on his own server in France. From the X posts on the development of the software, it seems that WebSpy boasts some impressive efficiency in terms of the low 6 kB/s network bandwidth required. This means that even over slow connections, the FFT and audio should be smooth and clear. The web interface also works well on mobile, providing a touch-optimized interface.

Youssef wrote in and wanted to share some additional information about how SharpIQ and SharpFFT work:

Under the hood, WebSpy streams both the radio signal and the spectrum display using two purpose-built compression codecs: SharpIQ for the channel data and SharpFFT for the FFT display.

A key design choice is what gets streamed: unlike most web receivers, which demodulate on the server and send you compressed audio, WebSpy sends the raw IQ signal of the tuned channel and does all the demodulation right in your browser — the same DSP chain as the gold standard SDR#. This matters more than it might sound: with server-side audio you're listening to a lossy rendition of what the server decided to demodulate, with voice-codec artifacts baked in; with local IQ, the actual signal arrives at your machine, so demodulation, filtering and mode changes happen instantly and the audio quality is limited only by the signal itself, not by an audio codec.

Unlike general-purpose compressors, SharpIQ and SharpFFT were designed from the ground up for radio: they adapt in real time to what's actually happening on the band, spending bits only where there is information worth keeping, while preserving the weak-signal fidelity that SDR users care about — a CW signal buried near the noise floor comes through intact.

The result is that a complete listening session — channel IQ, live spectrum, waterfall and all — typically fits in about 5 kB/s, a fraction of what conventional audio streaming would need. That's low enough to comfortably operate a remote receiver over a modest mobile connection, which is precisely what makes a full SDR experience in a browser tab practical — nothing to install, nothing left behind, just a tab you can close; and at 5 kB/s the stream itself hides in the noise of ordinary web traffic. Discreet SIGINT, if you're so inclined.

WebSpy: Airspy Web UI Desktop Interface
WebSpy: Airspy Web UI Desktop Interface

 

Exploring the Art and Science of Spectral Painting with SDR

Thank you to Paul Maine, who wrote in and wanted to share some experiments he and Gary Schafer have been doing with spectral painting. Spectral painting is the art of drawing pictures directly on the spectrum waterfall, which a software-defined radio makes visible. Paul has written the post below:

What happens when radio technology meets digital artwork? The result is something fascinating called Spectral Painting—the ability to create images that appear inside the radio frequency spectrum.

Gary Schafer (@signalgalaxiesunlimited) and Paul “The SDR Guy” Maine (@paulmaine6433) have teamed up to explore this unique combination of software-defined radio, signal processing, and creativity. Together, they have created companion videos on Spectral Painting and released them at the same time, each approaching the topic from a different perspective. For the best experience, it is recommended to watch Gary’s video first, followed by Paul’s practical demonstration.

Gary begins the journey by diving into the theory behind Spectral Painting. Using GNU Radio flowgraphs and GNU Octave scripts, he explains how images can be transformed into signals and displayed within the frequency spectrum.

Paul then takes Gary’s GNU Radio flowgraph and GNU Octave scripts from theory into practice. Using multiple SDR platforms, he demonstrates how to transmit spectral images using both the HackRF and TRX-DUO SDRs. He then completes the process by receiving and displaying the images using several different SDR receivers, including the RTL-SDR V3, RTL-SDR V4, and Airspy HF+.

Together, these videos provide a complete journey—from understanding the science behind Spectral Painting to seeing it come alive on real SDR hardware.

Below is an example screen capture of Spectral Painting in action.

Spectral Painting Example
Spectral Painting Example

Start with Gary’s video to learn the concepts and signal processing techniques:

Creating Spectral Paintings using Gnu Radio Companion (and other open source tools)

Then watch Paul’s video to see Spectral Painting transmitted and received using real SDR equipment:

E30 Spectral Painting

Demod: An iOS/iPadOS Client for rtl_tcp, SpyServer and KiwiSDR

Thank you to Alphonse Romero for submitting news about the release of his new iOS and iPadOS SDR receiver app called Demod. Demod is a network client that connects to remote SDR servers, so it can be tried out immediately with no dongle needed at all. 

The app works as a client for rtl_tcp, SpyServer (Airspy and RTL-SDR), and KiwiSDR, all in a single app. It features a Metal-accelerated waterfall and spectrum display, AM/NFM/WFM/USB/LSB/CW demodulation, and adjustable bandwidth, gain, and squelch. Other features include frequency memories with CSV import and export, AirPlay and Lock Screen controls, and native layouts for both iPhone and iPad. It can also browse and connect to public SpyServers directly from within the app, which is how it can be used with no hardware of your own. The developer notes that it collects no data, with no ads or tracking.

Alphose writes that Demod is a solo project and is available on the US App Store for US$9.99. More information and screenshots can be found on the project website, and the app itself is available on the App Store.

The developer has also provided us with 15 free codes that we will be giving away in one week. To enter the giveaway, simply comment on this post (make sure to include your email address in the comment so that we can send you the code), the X post, or the Facebook post. (UPDATE: ALL CODES HAVE BEEN ALLOCATED NOW, THANKS!)

Demod iOS SDR App
Demod iOS SDR App

InmarScope: An Inmarsat AERO and STD-C Decoder with Multichannel Decoding and Automatic Call Following

Over on the SignalsEverywhere YouTube channel, Sarah Rose has released InmarScope, a multichannel L-band Inmarsat decoder that connects directly to an RTL-SDR, Airspy, or HackRF. The software can receive and decode both aeronautical (AERO) and maritime (STC-C / EGC) traffic at the same time. Decoders are dropped directly onto the aligned FFT and waterfall by holding CTRL and left-clicking, and the software lets you stack Aero MSK (600/1200 bps), high-rate OQPSK (10500 bps), AMBE voice (8400 bps), and Inmarsat-C BPSK decoders side by side.

One of the more interesting features is automatic voice-call following. By monitoring the 10500 baud forward-link channels, InmarScope can receive C channel voice assignments and automatically retune the SDR to the assigned frequency, lock the carrier, decode and record the AMBE call, and then hop back to where it was. There is also a two-SDR mode that dedicates a second radio to voice with a live split-view spectrum so one radio stays on the P control channel while the other tunes to voice calls. For assignments that never get broadcast, there is also a Call Hunter feature that uses a squelch threshold to automatically drop the decoder when a call appears. When a call is playing, the built in flight map also decodes the aircraft hex ICAO address and looks it up on airplanes.live, showing the plane's position and route in real time.

Recent updates have added a community-editable band plan, message search and filtering, an IQ recorder that also captures the seconds before you hit record, and a web dashboard for browsing decoded data from a phone.

The software is completely open source on GitHub, and the C++ code can be compiled from source, or a precompiled Windows build is available on sarasforge.dev for $15, with Sarah's Patreon patrons getting it free.

We note that Inmarsat signals such as AERO and STD-C/EGC can be received with our RTL-SDR Blog L-band Patch Antenna, which is available in our store.

Multi-Channel Voice Following Inmarsat Decoder for Windows!

Decoding Inmarsat in 2026

Airspy 2026 Summer Sale: 20% Off All Airspy Products

Airspy has just announced its annual summer sale, offering 20% off all Airspy products from June 27 to July 4, 2026. 

  • Airspy R2: US$169.00 US$135.20
  • Airspy Mini: US$99.00 US$79.20
  • Airspy HF+ Discovery: US$169.00 US$135.20
  • Airspy SpyVerter R2: US$49.00 US$39.20
  • YouLoop Antenna: US$39.95 US$31.96

The sale is active at all participating resellers, which includes our own store, where we have the YouLoop on sale for US$31.96, including free shipping to most countries worldwide (excluding tariffs!). 

A New SDR# Panadapter Plugin

Thank you to Marco Argilli (IU4HMY) for writing in and sharing with us the release of a new SDR# Panadapter plugin that turns the popular RTL-SDR- and Airspy-compatible program SDR# into a panadapter for your transceiver. A panadapter gives you a live spectrum and waterfall view of the band around your radio's tuned frequency, which makes it much easier to spot activity, find clear frequencies, and visually navigate a busy band. Synchronization between the radio and SDR# is handled by OmniRig, so as you tune your transceiver, the panadapter display follows along.

To use the plugin, you connect your SDR to your transceiver's IF or antenna output, then set the receiver IF frequency and a per-mode offset in the plugin settings, with changes saved to a JSON config file. The plugin also has band presets, where a right-click on a preset button stores a snapshot of frequency, demodulation mode, and zoom level, so you can recall a favorite spot instantly. SDR# version 1921 or newer and the .NET 9 framework are required, and it runs on Windows 8, 10, and 11.

There are a couple of limitations worth noting. Marco recommends using Center Frequency mode for the best performance, and because OmniRig exposes the frequency as a 32 bit COM value, frequencies above around 2.1 GHz are not supported. The plugin does not appear to be open-source, but it is free for personal and non-commercial use.

SDR# Panadapter Plugin Screenshot
SDR# Panadapter Plugin Screenshot