Category: RTL-SDR

MagicSDR: Streaming Audio over UDP to Decoders like Multimon-NG

Back in May 2021 we first posted about the release of MagicSDR, which is an Android and iOS SDR app that receives data from an rtl_tcp server elsewhere on your network. Apart from the RTL-SDR, MagicSDR also supports the SDRplay, LimeSDR, HiQSDR, Flex 6-seris and sound card based radios.

Recently MagicSDR programmer Vlad wanted to share a new feature in MagicSDR that allows users to stream audio over UDP. He notes that this allows external data decoders such as direwolf or multimon-ng to be used. The example in the video below shows MagicSDR sending demodulated audio over UDP to multimon-ng running on the same Android device.

Decoding Morse CW on android phone

MagicSDR sending demodulated audio over UDP to multimod-ng decoder

An Improved ExtIO for RTL_TCP

Back in 2020 we posted about a modified ExtIO interface which exposed advanced RTL-SDR driver settings such as decimation, manual gain and tuner bandwidth and filtering controls. These features allow users to tune filters to avoid ADC overload and to overall fine tune reception better, especially for narrowband signals. ExtIO is the driver interface used by some popular SDR programs like HDSDR.

Thanks to contributor Ladislav (OK1UNL) for notifying us about an improved version of that ExtIO interface by DG2YCB.

DG2YCB improved version adds the following features:

  • Auto-Q: The RTLSDR stick automatically switches to direct sampling (Q channel) for frequencies below 24.5 MHz and direct sampling is automatically disabled when tuned to any frequencies above 24.5 MHz.
  • My ExtIO_RTLTCP_improved.dll drivers set the chip AGC to ON, which brings you a better RX sensitivity than the original version.
  • My ExtIO_RTLTCP_improved.dll drivers are available in the following versions:
    • ExtIO_RTTCP_improved1.dll uses autoGain for the tuner gain.
    • ExtIO_RTTCP_improved2.dll uses optimized manual gain settings for the tuner gain, which shall prevent that the RTLSDR stick is overdriven on VHF / UHF frequencies.
    • ExtIO_RTTCP_improved3.dll has Auto-Q as well as the optimized gain settings profile but has a more sophisticated GUI, so that you can adjust more parameters manually. (Currently available as beta version.)

This ExtIO also allows users to connect to an RTL-SDR when software like HDSDR is run on Linux via an emulator such as WINE.

Ladislav also pointed out that DG2YCB has improved versions of WSJT-X and JTDX that might be of interest to some.

ExtIO Improved dll 3

ESAR – Extraordinarily Simple AIS Receiver written in C

Thank you to Richard Gosiorovsky for submitting his latest SDR project called ESAR (Extraordinarily Simple AIS Receiver). AIS stands for Automatic Identification System and is used by marine vessels to broadcast their GPS locations in order to help avoid collisions and aide with rescues. An RTL-SDR with the right software can be used to receive and decode these signals, and plot ship positions on a map.

Richards code comes as raw C code, so you will need some knowledge on C code compiling to use it. Being so simple, the code is also a great resource for learning how to access data from an RTL-SDR, and write a decoder. Richard writes:

[ESAR] takes less then 300 lines of programming code and no additional software is necessary (like SDR# or audio piping).

It was intended mainly as exercise in digital signal processing.

All you need is RTL-SDR dongle with driver and rtl_tcp command. Simple dipole antenna is sufficient. If all this you have just compile C code (in the attachment) using MS Visual Studio.

Before running ESAR run rtl_tcp command with this parameters:

rtl_tcp.exe -f 162e6 -s 300000 -a -p 2345 -g 48.0

It comes with GNU licence so converting output to NMEA format or any graphical output is free choice of other SDR enthusiasts.

Richard has shared the C code file directly with us, and it can be downloaded from our server here.

ESAR Code Screenshot

RTL-SDR Blog V3 Dongle and SDR# Spotted on The Secret of Skinwalker Ranch TV Show

An RTL-SDR Blog V3 dongle and multipurpose dipole antenna set has been spotted in action on the popular TV Show "The Secret of Skinwalker Ranch" in Season 3 Episode 7. Skinwalker Ranch is a History channel conspiracy theory reality TV series where a team of scientists and researchers are sent to look for various explanations for "otherworldly" activities supposedly occurring on the ranch. In the past we have also seen an SDRplay RSP software defined radio with SDRuno software featured in a previous episode.

In this episode the team are drilling into a mysterious mesa rock formation on the ranch, and are monitoring the RF spectrum with an RTL-SDR during the drill. They take note of a mysterious signal at 1.6 GHz that appears during the drilling.

Screenshots from "The Secret of Skinwalker Ranch" Season 3 Ep 7

Low Cost Shielding Idea for Plastic RTL-SDRs

Generic RTL-SDRs that come with a plastic enclosure can be prone to picking up interference directly via the PCB itself. Higher end RTL-SDRs generally come with a metal enclosure.

Thanks to Alan R. for submitting a low cost idea he's come up with for shielding his plastic RTL-SDR dongles. Alan writes:

I’ve used this attached method with quite a bit of success for shielding the RTL dongle. It’s just a fizzy orange tube with two holes drilled at each end and some sticky metal insulating tape, which can be bought at any DIY store. Once the USB adapter and RTL dongle are inside they fit snuggly and any standard printer cable with reasonable length works well. Usually this allows for shorter coax connections which again helps keep the signal to noise level reasonable. I opted for a USB with a ferrite core at either end and I also added one to the coax - just because.

If you leave the antenna detached and tune in to any FM radio station you get a strong signal, and as soon as you put the RTL-SDR inside the insulated tube the signal stops. Needless to say if you plug the antenna in then the FM radio comes through with a strong signal. It certainly helps cut down a lot of FM broadcast noise (cheaply!)

I’m not using any band stop / band pass / pre amps and currently I’m receiving loud and clear satellite transmissions - NOAA / Meteor 2. I can even grab the telemetry from AO-73 Funcube with no problems. As the USB is shielded too and is away from the computer it also helps. Plugging the dongle directly into the computer tends to pick up a lot of unwanted noise.

The only thing to watch is it can get a little hot, so some common sense when using it (especially on a hot day). The other advantage is the weather proofing should you get caught in rain!


TechMinds: Testing the ISM Packet Decoder Plugin for SDR Sharp

Over on the TechMinds YouTube channel Matt has uploaded a video demonstrating the use of the ISM Packet Decoder plugin for SDR# which was released a few months ago. The plugin authors website also contains more information about the installation and features of plugin.

The plugin makes use of the well known rtl_433 software behind the scenes, which is a command line based RTL-SDR compatible decoder for various wireless ISM band devices such as weather stations, car keys, tire pressure sensors, doorbells and various other remote controlled devices. The plugin GUI makes using and displaying data from rtl_433 much more convenient.

ISM Packet Decoder Plugin For SDR Sharp - RTL 433

Probing a Cable Internet + TV Line with RTL-SDR USB

Thank you to Adam from Double A Labs for submitting his latest YouTube video where he uses his RTL-SDR to probe the coaxial cable that provides his broadband internet and cable TV. In the video Adam explains how hybrid fiber-coaxial internet and TV broadband networks (such as Comcast/Xfinity) work, and how the Specktrum software can be used with an RTL-SDR to explore the spectrum on these cables. Adam writes:

What I found was pretty interesting, including a few unmodulated analog TV carriers on the line producing a black screen on my TV. I also explain how coaxial broadband networks work (bi-directional amplifiers, upstream/downstream splits, etc.) and how internet service providers are upgrading them.

How Broadband Cable Networks (Xfinity etc.) Work and Probing One with a Spectrum Analyzer (RTL-SDR)

Feeding ACARS Data to

Thank you to a contributor for submitting an article about, which is an ACARS/VDL2/HFDL/Satellite ACARS aggregation site. The article below it attributed to Kevin Elliott and was edited by Frank Vance. They would also like to attribute the large group or volunteers at

One of the most popular hobbyist uses of SDR is receiving and decoding vehicle information data such as ADS-B for aircraft or AIS for marine traffic.  Some hobbyists have been banding together to exchange their mutual data streams to provide coverage over wide geographic areas.

One of the largest and most successful such projects in the aviation realm is ADS-B Exchange (, where over 8,000 volunteer feeders provide ADS-B data to a global aviation map in real time.  

But modern air carriers have much more data to and from their aircraft than just the position information from ADS-B.  In the 1970s, ACARS was created to carry that traffic.  Today, ACARS is seen on its own frequencies on VHF, embedded in AVLC on the VDL2 VHF frequencies, on HF (shortwave) frequencies using the HFDL network of stations worldwide, and on satellite on both the Inmarsat (ACARS over AERO, or AoA) and the Iridium (called ACARS over Iridium, or AoI) systems. ( is a project that has been under development for a while to aggregate ACARS data in the same way ADS-B Exchange is aggregating ADS-B data.  Under the capable leadership of Kevin Elliott (, software development has progressed to the point that new feeders are actively being sought to improve the global coverage and provide a broader base of data to improve the decoding.

With a wide variety of data sources, this is a collaboration project that is open to all levels of SDR hobbyists.  A simple RTL-SDR.COM unit attached to a Raspberry Pi with a smaller antenna works well with the VHF coverage.  Depending on one's interest level, an HFDL feeder may require multiple SDRs with much broader frequency range, capable of reception in the sub-30 MHz bands.  The L-band based Iridium AoI uses a small antenna as well, but requires a wide bandwidth SDR.  Finally, reception of the C-band Inmarsat (AoA) traffic may involve a moving dish antenna of at least 6 foot diameter to obtain usable signals.

What kind of data is seen in ACARS?   One can observe weather conditions aloft, messages to/from the carrier operations staff, information about the origin and destination of the flight, and technical data on the aircraft operation (not all of which can be decoded at this time.)  Additionally, the HFDL and satellite feeds offer location information out of sight of the traditional ADS-B coverage, such as over the oceans and polar regions.
The About page at ( has plenty of good information to help anyone get started with feeding, including links to popular software packages useful for running different types of feeders.  Support is available on the #airframes-io channel ( on the ADSBExhange Discord server (
Additional information about setting up a receiver/feeder for HFDL, Inmarsat L-band, Inmarsat C-band, and Iridium L-band is available on The Bald Geek's GitHub page: joining with the dozens of volunteers already feeding and contributing software updates to the project. Map ACARS Messages