Using CubicSDR, rtl_433, MQTT and Telegraf to Stream Live Data to InfluxDB

Nimrod makes his own sourdough and wanted a way to track the temperature and humidity of the bread making environment. To do this he's set up a system involving rtl_433 on a Raspberry Pi which live streams all of his home temperature/humidity sensor data into InfluxDB. The program rtl_433 is software for the RTL-SDR that allows users to receive data from many different brands of home weather/temperature sensors, as well as many other wireless ISM band devices. InfluxDB is a type of database that specializes in storing and displaying time series data from sources like sensors.

The chain of data starts with rtl_433 which collects the temperature sensor data via an RTL-SDR. The output of rtl_433 is sent to Mosquitto, an MQTT messaging protocol server. A program called Telegraf then subscribes to the MQTT queue, and parses and transmits the metrics to InfluxDB. InfluxDB finally records the data, and provides graphical plots. 

Nimrod's post is a full tutorial showing how to download and set up each of the programs used in the system, and how to view the data collected with InfluxDBs graphing system.

RTL_433 temperature graphs via InfluxDB
RTL_433 temperature graphs via InfluxDB
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SignalsEverywhere: Decoding Digital Data via Audacity, Mulitmon-ng and MiniModem

SignalsEverywhere is back this week and in her latest video Sarah talks about using a combination of Audacity, Minimodem and Multimon-ng to decode digital data that could be obtained from an SDR or other signal source.

Sarah was interested in the 2020 Hackasat space security challenge and specifically in completing the 56k Flex Magic challenge which consists of an emulated signal from an old 56k modem. Within the 56k modem signal is secret information required to complete the challenge.

Sarah first shows how to use Multimon-ng to decode the DTMF tone section of the signal. These are the tones heard when dialling on a landline phone. She then goes on to show how to use Audacity in spectrogram mode to take a closer look and analyze the next chunk of the signal. Then by using the information gained about the signal from the spectrogram analysis she is able to decode the data via minimodem.

Audacity Decoding Data?! Using Audacity Multimon-ng and Minimodem to Decode Digital Audio Data!

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Tech Minds: Testing Antennas with the VNA N1201SA / PS100

Over on his channel Tech Minds has uploaded a new video where he tests the N1201SA / PS100 vector impedance analyzer. This is a US$160 antenna analyzer from China that allows you to measure the VSWR of your antennas. In the video Tech Minds explains a bit about VSWR, and goes on to show the unit in action on several of his antennas.

Compared to the NanoVNA V2 these units seems less useful with a smaller frequency range, and are also more expensive. The unit is also only 1-port, meaning that it can only do S11 measurements and cannot analyze devices like filters. But on the other hand it does come in a metal case with a battery and has a fairly easy to understand and use interface.

Easily Check Your Antennas Tuning - VNA N1201SA / PS100

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Frugal Radio: 2020 SDR Guide Ep 2 – Using Free Online SDRs

Over on his YouTube channel Frugal Radio has released the second episode in his 2020 SDR Guide series. In this video, Frugal Radio shows how to connect to remote SDRs such as KiwiSDR OpenWebRX, WebSDR, SDR-Console v3 Servers, and SDR# SpyServers. He shows how to use these remote SDRs to monitor long range aviation channels, amateur radio operators, and VHF Public Safety channels in the US. He also demonstrates how to decode HFDL signals from aircraft using WebSDR and free software, and verifies the aircraft locations via online tracking sites.

2020 SDR Guide Ep 2 : How to use over 500 remote SDRs free online (webSDR, KiwiSDR & HFDL decode)

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Tracking Wild Bats with SDRs – Featured in Science Magazine

Recently research from Tel-Aviv University by Sivan Toledo et al. involving the use of USRP SDRs to track wild bats was published in Science.  The Journal Science (aka Science Magazine) is one of the world's top peer reviewed academic journals.

Sivan and his collaborators developed inexpensive 434 MHz band tracking tags for bats that emit radio pings every few seconds. These pings do not contain any location data, however the location is accurately tracked by several USRP SDRs with high accuracy GPSDO oscillators set up around the target tracking area. A radio direction finding technique known as "time difference of arrival" or TDoA is used to pinpoint the location of each tag. Sivan writes:

A wildlife tracking system called ATLAS, developed by Sivan Toledo from Tel-Aviv University in collaboration with Ran Nathan from the Hebrew university, enabled a science breakthrough reported in an article in Science that was published yesterday.

The system uses miniature tracking tags that transmit radio pings in the 434 MHz bands and SDR receivers (Ettus USRP N200 or B200). Software processes the samples from receivers to detect the pings and to estimate their time of arrival. The overall system is a "reverse-GPS" system, in the sense that the principles and math are similar to GPS, but the role of transmitters and receivers is reversed. A youtube video explains how the system works. SDR-RTL dongles can certainly detect the pings, but their oscillators are not stable enough to accurately localize the tags.

The system has been used to track 172 wild bats (in batches, some consisting of 60 simultaneously-tagged bats). The results showed that bats can make novel shortcuts, which indicates that they navigate using a cognitive map, like humans. The system, and other ATLAS systems in the Netherlands, England, Germany, and Israel are also tracking many different animals, mostly small birds and bats.

The video below shows the bats being tracked on a map accelerated to 100x.

434 MHz Tracking Devices that Attach to Wild Bats
434 MHz Tracking Devices that Attach to Wild Bats

The Science article itself is mostly about the discoveries on bat behaviour that were made by the system. However the YouTube video embedded below explains a bit more about how the technical radio side works. 

A Technical Overview of the ATLAS Wildlife Tracking System

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Controlling Frequency in SDR# with a Barcode Scanner

Thank you to Manuel Lausmann for submitting his YouTube video showing how he has set up a system that allows him to rapidly change frequencies in SDR# with a barcode scanner and some barcodes printed via an online generated. This might be an interesting way for non-technical users to easily change frequencies on demand, for example in a public demonstration of various radio channels.

We note that the video is narrated in German, but you can use the YouTube auto-translation feature to get English subtitles.

Schneller Frequenzwechsel mit einem Barcode Scanner

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Testing a YouLoop on an RTL-SDR Blog V3 with Direct Sampling

Thank you to Frugal Radio for submitting a YouTube video where he tests the YouLoop on an RTL-SDR Blog V3 running in direct sampling mode. The YouLoop is a passive HF loop antenna that requires a highly sensitive SDR like the Airspy HF+ Discovery to work at its full potential. However, in direct sampling mode the RTL-SDR Blog V3 does have enough sensitivity to work with the antenna to some extent thanks to the HF amplifier that is used on the direct sampling circuit. In the video Frugal Radio demonstrates the YouLoop receiving various HF signals.

Will an AirSpy YouLoop work with an RTL-SDR v3 on HF in direct sampling mode? It shouldn't...

We also note a second video by Bartłomiej Marcinkowski which shows an RTL-SDR Blog V3 in direct sampling mode running with a DIY YouLoop and MiniWhip. The MiniWhip does have increased signal strength, but the YouLoop is still usable and may be a better choice in the presence of interference. Later in the video he compares the RTL-SDR Blog V3 with MiniWhip against the Airspy HF+ Discovery with DIY YouLoop. 

RTL-SDR v3 & YouLoop vs RTL-SDR v3 & MiniWhip vs AirSpy HF+ Discovery & YouLoop [80m,40m,20m]

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Electrosense+: Global Network of RTL-SDR Sensors with Decoding of FM/AM ADS-B AIS LTE ACARS

Back in late 2019 we posted about the Electrosense network which is an open source project aiming to deploy radio spectrum sensors worldwide. The idea is to help analyze and understand radio spectrum usage across the globe. Each sensor consists of an RTL-SDR, Raspberry Pi and an optional downconverter to receive the higher bands.

Recently Dr. Sofie Pollen wrote in and informed us that they have recently upgraded Electrosense and now users can use any sensor on the network to actually decode signals remotely over a web browser. The currently supported demodulators/decoders include FM/AM, ADS-B, AIS, LTE base station info and ACARS. This makes the Electrosense network kind of similar to the KiwiSDR or OpenWebRX SDR network where there are also various decoders built into the web software.

To test it out you need to create an Electrosense account at electrosense.org. Once logged in, go to "My Electrosense" on the top right, and choose "Spectrum Decoder". You can then choose from a number of Electrosense contributors stationed around the world. Once the waterfall is displayed you can click on signals to decode and listen to them, or change the decoder. Changing to ADS-B or AIS will bring up a map with decoded aircraft or boat positions. Changing to ACARS or LTE will show a text window with the decoded information.

A full electrosense kitset can be purchased from Jetvision, however Sofie notes that they do ship free sensors to some people who cannot afford the kit, and you can apply to increase coverage in your area via this link.

Currently active electrosense sensors
Currently active Electrosense sensors
Electrosense web GUI decoding a wideband FM signal
Electrosense web GUI decoding a wideband FM signal
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