Analyzing 433 MHz Transmitters with the RTL-SDR

Over on his blog, Yashin has written a post showing how to analyze 433 MHz transmitters using several methods. Devices that transmit using low power 433 MHz are common and often include devices such as weather monitors, power monitors and alarm sensors.

To show his analysis methods Yashin used an ASK modulated FS1000A 433 MHz transmitter connected to an Arduino Teensy microcontroller. He first uses GQRX and baudline together with an RTL-SDR in Kali Linux to test that the transmitter is working and to visually inspect the RF spectrum. Then he shows how to use GNU Radio to receive the 433 MHz transmitter and how to record an audio file. The final tool he shows how to use is rtl_433 which will automatically decode the data into binary strings using the analysis option.

ASK 433 MHz Transmitter
ASK 433 MHz Transmitter
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Visualizing Doppler Signal Reflections with the RTL-SDR

Over on his blog DE8MSH has uploaded a video showing a timelapse of some Doppler signal reflections he recorded. He shows more information about his Doppler recording setup on this previous post which shows that he was even able to get a Doppler reflection from the ISS using the French Graves radar.

When an airplane or meteor reflects a signal from a strong transmitter such as an ATIS signal or the Graves radar in France, the received reflected signal frequency will change as the plane or meteor comes towards or away from your receiver. This is due to the Doppler effect. Its effect can be observed as the sloping lines shown in the video.

To do the recording, DE8MSH used HDSDR together with spectrum lab and an RTL-SDR.

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Receiving Signals from the Lunar Reconnaissance Orbiter with an RTL-SDR and WiFi Grid Antenna

Gat3way has recently posted on his blog an article showing how he was able to receive a signal from the Lunar Reconnaissance Orbiter (LRO) using only an RTL-SDR, WiFi grid antenna and a low noise block (LNB). The LRO is a NASA spacecraft which is currently orbiting and being used to create maps of the moon.

The LRO transmits a tracking, telemetry and control (TT&C) signal at 2271.125 MHz which is in the S band (2 to 4 GHz). Since the S band frequencies are commonly used for Indovision satellite TV, gat3way was able to find a cheap LNB which could downconvert the GHz level S band frequencies down into a frequency receivable by the RTL-SDR. For the antenna he used a high 22dBi gain motor controlled WiFi mesh parabolic grid antenna.

After aiming the antenna at the moon, gat3way was able to clearly see the LRO carrier signal in the RTL-SDR waterfall as shown in the image below.

WiFi Parabolic Mesh Antenna for the S Band
WiFi Parabolic Mesh Antenna for the S Band
LRO Signal Received by RTL-SDR, LNB and WiFi antenna.
LRO Signal Received by RTL-SDR, LNB and WiFi antenna.
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Automatic Heatmap Logging on a Raspberry Pi using an RTL-SDR and RTL_POWER

Amateur radio hobbyist DE8MSH recently wrote in to let us know about a project he has been working on. His project involves using a Raspberry Pi B and RTL-SDR to automatically log a wide band heatmap using rtl_power. Rtl_power is a command line tool that will log signal strengths to a csv file using the RTL-SDR over a very large definable bandwidth.

To do the automatic logging the Raspberry Pi runs rtl_power for 23 hours constantly writing data to a mounted hard drive. After 23 hours the heatmap image is calculated and then uploaded to a webpage at http://qth.at/de8msh/listheatmaps.php. The scheduling is performed by a cron job.

DE8MSH has also been working on a second related project over at http://www.qth.at/de8msh/hm/pic.html. The heatmap on this page shows various transmissions from weather balloons. As you mouse over those transmissions, the QTH (location) of those weather balloon transmissions is shown as well as the frequency and time of where the mouse pointer currently is.

Raspberry Pi Automatic Heatmap Logging with rtl_power
Raspberry Pi Automatic Heatmap Logging with rtl_power
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Monitoring Multiple AM channels with RTL-SDR Airband

A new command line program for the RTL-SDR called RTL-SDR Airband has recently been released. The program can be used to simultaneously monitor multiple AM channels per dongle. It is intended to be used with online streaming services like liveatc.net which provide live audio streams of air traffic control communications around the world.

Its features include

  • Decode multiple AM channels per dongle (within bandwidth frequency range)
  • Auto squelch and Automatic Gain Control
  • MP3 encoding
  • Stream to Icecast or SHOUTcast server
  • Low CPU usage on Windows (<4% on i5-2430m) thanks to SSE and AVX instructions
  • FFT using GPU on Raspberry Pi (50-55% CPU with default clock)
Monitoring Multiple AM Channels with RTL-SDR Airband.
Monitoring Multiple AM Channels with RTL-SDR Airband.
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RTL-SDR Based Coherent Multichannel Receiver

YO3IIU has written a post on his blog showing how he was able to create a coherent multichannel receiver using several RTL-SDR dongles all running on a single clock source.

To do this he used a CDCLVC1310-EVM board which provides up to 10 clock outputs and then connected four of the clock outputs to the clock inputs of four separate RTL-SDR dongles. He then uses a GNU Radio program to correlate the signals from each RTL-SDR stick.

Recently we have seen two applications of an RTL-SDR based coherent multichannel receiver used in passive a radar systems here and here.

Coherent Multichannel Receiver based on the RTL-SDR
Coherent Multichannel Receiver based on the RTL-SDR
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Transmitting DVBT HDTV from a Raspberry Pi to an RTL2832U

Over on his blog, OZ9AEC has uploaded a post showing how he was able to create a live HDTV transmitter out of a Raspberry Pi, a Raspi Cam module and a UTC DVB-T Modulator adaptor. As he does not want to interfere with commercial DVB-T broadcasts, he sets the module to transmit at 1.28 GHz, aka the 23 cm licenced ham radio band.

On the RTL2832U dongle side, he modified the RTL2832U Linux DVB-T drivers (not the SDR drivers) to work on the 1.3 GHz band. The intention of this camera is for it to fly on a rocket mission. In the YouTube video below he has uploaded some sample footage with the RTL2832U dongle receiving the stream from 300 meters away.

Rocketcam 1 test 3 (20140531_142625)

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Transmitting ADS-B with a HackRF and Receiving it with an RTL-SDR

Over on YouTube user Jiao Xianjun has uploaded a video showing how he was able to transmit an ADS-B signal from his HackRF One and receive it using an RTL-SDR with dump1090. He transmits a low power signal which shows a fake plane flying over the Senkaku islands.

Important Note: While this warning is also on the video we feel that we should re-emphasize that you should never transmit anything at 1090 MHz unless you are authorized to do so and are in a controlled RF environment.

ADS-B out by HACKRF and received by rtl-sdr + dump1090

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