Tagged: rtl-sdr

Open Source Close Call Monitor for RTL-SDR

Thank you to Fabian for writing in and sharing with us his newly released RTL-SDR close call monitoring software called "rtl-sdr-close-call-monitor". The software is open source and written in Python. It's main purpose is to log any signal peaks that appear within a defined frequency range. Over on the GitHub Fabian explains the software:

These scripts use an RTL-SDR device to detect peak signals on a user specified frequency range. The scripts can also make an automatic blacklist so that different sources of RF noise won't cause continuous false positives. There are two scripts provided as examples. The scripts can be used to monitor certain frequencies for a wide range of purposes such as:

  • In criminal investigations, a close-call RF signal monitor can be used to detect and track communication signals used by criminals. This can help law enforcement agencies gather intelligence and evidence, and even prevent future crimes from being committed. By analyzing the frequency and strength of signals emitted by communication devices, a close-call RF signal monitor can provide valuable insights into the movements and activities of suspects, allowing investigators to piece together a timeline of events and make informed decisions about how to proceed with a case.
     
  • In military operations, a close-call RF signal monitor can be used to identify and track enemy communication signals, providing valuable intelligence for strategic decision-making.
     
  • In scientific research, a close-call RF signal monitor can be used to collect and analyze data related to wireless communication systems, providing valuable insights for thesis projects and other research studies.
An excerpt of Fabian's close call monitoring Python code.

Hunting for Space Radio Pirates on the US Military Fleet Satcom Satellites

In the 70's and 80's the US government launched a fleet of satellites called "FLTSATCOM", which were simple radio repeaters up in geostationary orbit. This allowed the US military to easily communicate with each other all over the world. However, the technology of the time could not implement encryption. So security relied entirely on only the US militaries technological advantage at being the only ones to have radio equipment that could reach these satellites.

Of course as time progressed equipment which could reach the 243 - 270 MHz range of the satellites became common place, and the satellites began picking and repeating terrestrial broadcasts of things like cordless phones. These days the satellites are often hijacked by Brazilian radio pirates, who use the satellites for long range communications.

A common hobby of RTL-SDR users is to listen to these pirates. All you need is a simple antenna and to be based in a region where the satellites cover both your ground station and the pirates.

Over on YouTube the "saveitforparts" channel has uploaded an entertaining video overviewing the pirate phenomenon, and showing how it's possible to listen in using a cheap Baogeng scanner and RTL-SDR. He uses a homemade Yagi and cleverly makes use of an old security camera motorized PTZ mount to accurately aim the antenna. Once the Yagi antenna is aimed at the satellite, pirates can be heard on the radio.

Searching For Space Pirates On Old Military Satellites

On a previous post, we showed an interview by SignalsEverywhere and an anonymous Brazilian radio pirate who explains how and why they do what they do. If you search our blog for 'satcom' you'll also find several previous posts including examples of receiving SSTV from pirates.

Visualizing RF Fields in Augmented Reality with a tinySA-Ultra or RTL-SDR and Android Smartphone

The tinySA-Ultra is an affordable handheld spectrum analyzer that can be purchased for around US$130 on Aliexpress and authorized resellers such as R&L Electronics in the USA.

Recently on YouTube Manahiyo has used his tinySA-Ultra, and combined it with an RF EMC probe and an Android smartphone to create an augmented reality RF display. This is useful for measuring and visualizing the RF power around electronic devices for example. The code is entirely open source and released on GitHub. 

Manahiyo has also released an identical version that works with RTL-SDR dongles on GitHub as well.

In the past we've also posted about Manahiyo's previous work, in which he implemented a very similar augmented reality project using an RTL-SDR.

Augmented Reality EMC Probe with a tinySA-Ultra
[RadioFieldAR -tinySA-] Visualize radio wave strength. [電波可視化]

Listening in on Hollywood Reality TV Show Wireless Microphones with an RTL-SDR

Over on Reddit user u/mknlsn has posted an interesting use for his RTL-SDR. He happens to live next door to a Hollywoood reality TV show production and was able to use his RTL-SDR to listen in on the wireless microphones fitted to the cast. The wireless microphones used by the production appear to be simple analogue FM modulated, without any sort of security.

We remind readers to check local laws on this sort of use, especially if recording audio, as some countries and US states may have differing laws on what can be recorded, or even listened to live. This would likely be considered private communications, so recording and sharing would definitely be illegal in most regions. 

Recently we also posted about Frugal Radio using an Airspy SDR to listen in on wireless microphones from outside a theatre show.

Wireless microphones picked up by RTL-SDR

Hacking Beepers at a Fish & Chip Shop with an RTL-SDR and HackRF

Over on YouTube Paul from "Tall Paul Tech" has uploaded a video showing how he was able to reverse engineer the wireless protocol used by a simple restaurant beeper (aka 'burger pager') notification system that is used to let customers know when their food is ready.

By reading the label on the base unit, Paul found that the beeper system transmits at 433 MHz. He was then able to record it's transmissions with an RTL-SDR. Then using Inspectrum, he was able to determine the bit string and the symbol period.

From there he was able to use a GNU Radio program to replicate the signal, allowing him to use a HackRF to activate the beepers on demand.

In the past we've posted similar stories [1][2][3].

Hacking A Fish & Chip Shop

SDRDue Updated: Passive Radar Software for RTL-SDRs

Thank you to Daniel Kaminski for writing in and sharing with us news that he has recently updated his SDRDue Passive Radar software for RTL-SDRs. The major update is that thanks to NVIDIA CUDA GPU processing, the ambiguity function can now be calculated extremely quickly, allowing for very high frame rates. Daniel writes:

Last time I was playing with my Passive Radar. I finally created an ambiguity library which is a really fast 70 frame/s analyzing a continuous string of data 2*1024*1024 bits per frame. This allowed me to record signals from slowly moving cars in real-time. I used a normal TV antenna without any modifications in one dongle mode. To support the library I created a Passive Radar program with all the parameters available for tuning. The code is open and available on GitHub. The movie is available on my website Passive radar | Web page od Daniel M. Kamiński (umcs.pl).

SDR Due Passive Radar
SDR Due Passive Radar

Job’s Radio Telescope Observes Maser W3(OH)

Over the past few years we've seen a lot of interesting observations coming from Job's Radio Telescope, which is Job Geheniau's 1.5m dish connected to an RTL-SDR (with additional filters and LNAs). He has done things like mapped the galaxy via the Hydrogen line, observed red supergiant stars, imaged a supernova remnant, detected a Pulsar, and measured the basis for the dark matter hypothesis.

In his most recent work Job has managed to detect the W3 star forming region at the Hydroxyl (OH) frequency of 1665.405 MHz.

W3 is an enormous stellar nursery about 6200 light-years away in the Perseus Arm, one of the Milky Way galaxy's main spiral arms, that hosts both low- and high-mass star formation. - Source

Hydroxyl (OH) can be observed both in emission and absorption. Emission frequently manifests itself as maser emission which is of specific interest. Energy Levels of OH Diatomic molecules like OH have numerous energy levels as they not only have electronically excited levels, but they can also vibrate and rotate. Both rotation and vibration are quantized and give rise to the large number of levels. Because of the wealth of energy levels, OH can be observed at various wavelength in the optical, infrared and radio regime. - Source

Over on the RTL-SDR Facebook group (not affiliated with this blog), Job has described his experiment in more detail (link requires a Facebook account and membership). He writes: 

As you may know or not...., I have been busy the last few weeks trying to detect maser W3(OH) with my 1.5-1.9 dish. The W3 complex lies in a darkened part of the Perseus galactic arm, at a distance of ∼2.2 kpc, and is one of the most intensively studied star-forming regions in the Milky Way Galaxy. Quite a challenge! It looks like I have a hit now after all.

Adjusting the Feed, calibrating the position of the dish and a lot of trial and error and a lot of patience seem to be leading to a result after all.... For now, I will keep this as my W3(OH) registration at 1665.405 MHz. Taking into account the Vlsr of currently 17 km/s (speed of earth and rotation around the sun), the final result comes close to the correct measurement. 1665.789 MHz = -32.22 km/s. Vlsr according to my calculations in terms of location and time is 17 km/s. -32-17=49 km/s. I think and hope that -49 km/s is the correct velocity of W3(OH) also considering the reasonably clear peak in the measured values in the graph.

These W3(OH) results were done with a special 1665 bandpass filter and 2 mini circuits lna/s. I will keep measuring for a while in the coming days, but soon I will switch back to another Feed over, namely the now under construction 611 MHz Feed with associated bandpass filter to once again 'capture' pulsar B0329+54. My ultimate goal with this dish!

I was very close last six months, but after extensive research with fellow radio amateurs we unfortunately could not confirm with 100% (!) certainty that the pulsar was detected at 1420 MHz with the 1.9 dish.

Also that research continues with longer exposure times and now research at 611 MHz, there is still some soldering and drilling and sawing to be done..... But first things first. Glad with this result anyway. Takes a lot of perseverance and patience.

Job's Radio Telescope detects Maser W3(OH).
Job's Radio Telescope detects Maser W3(OH).
Job's Radio Telescope detects Maser W3(OH).
Job's Radio Telescope detects Maser W3(OH).

Tech Minds: Testing an RTL-SDR Wideband Scanner with WebUI

Over on YouTube Matt from the Tech Minds YouTube channel has put up a video demonstrating an open source program released on GitHub called "RTL SDR Scanner", or "rtl-sdr-scanner-cpp". This program is compatible with RTL-SDR and HackRF software defined radios, and allows users to record multiple analogue FM audio channels within the active bandwidth simultaneously. 

To get a wider bandwidth, you can use a HackRF as your SDR, or you can also use multiple RTL-SDR dongles, or a device like the KrakenSDR which has multiple RTL-SDRs built into it. Alternatively, you can also have the software scan a much larger swath of bandwidth, however this could result in some transmissions being missed. 

The audio is recorded as a wav file, and can be accessed through a web UI. We note that currently only FM recordings are supported but AM may be supported in the future.

RTL SDR Scanner - FULL Bandwidth Recording With WEB UI