Frugal Radio: Listening in to Live Theatre Wireless Microphones with an SDR

In one of his latest videos, Rob from the Frugal Radio YouTube channel gives us an interesting alternative way to enjoy a theatre show by demonstrating what he heard on his Airspy SDR when taking it to a Christmas theatre show. In a modern theatre show the actors and actresses typically wear hidden wireless microphones and earpieces, allowing their voices to be amplified and instructions from the producers and directors to be heard. If close enough, these devices can easily be picked up with a SDR and antenna.

In his video Rob explains what sort of radio devices and frequencies are used at the theatre, and despite a few set backs he manages to listen in on these devices from the lobby and from just outside the theatre complex. 

Some of the things he hears includes backstage instructions from the directors and production team and of course audio from the performers, including backstage conversations.

2021 SDR Guide Ep 12 : SDR Theatre fail with my AirSpy R2 and RTL-SDR dipole kit

A Comprehensive Beginners Guide to HRPT Weather Satellite Reception

Over on his blog Derek (OK9SGC) has recently uploaded a very comprehensive beginners guide to receiving HRPT weather satellite images. HRPT reception can be a little daunting as it requires a good L-Band dish setup which involves choosing and building a feed, and importantly, a way to track the satellite with the dish as it moves across the sky. Tracking can be achieved manually by hand, but that can be very difficult and so a motorized tracking mount is recommended.  

This is unlike the much easier to receive NOAA APT or Meteor LRPT satellite signals in the VHF band which can be received by a V-dipole antenna, or the geostationary GOES HRIT satellites that can be received with a WiFi grid dish and LNA. Both of which do not require tracking.

The advantage of HRPT however, is that you end up with high resolution, close-up, and uncompressed images of the earth. For example Derek notes that NOAA APT gives 4km/px resolution, and Meteor LRPT gives much better 1km/px resolution but it is heavily compressed. Whereas HRPT gives peak resolutions of 1km/px uncompressed. There are also nine satellites in operation sending HRPT, so there are more opportunities to receive.

Derek has created a very comprehensive beginners guide that covers almost everything from purchasing and building the hardware, to finding and tracking the satellites, to setting up the software and decoding images. He notes that an RTL-SDR can be used as the receiver, and that a WiFi dish with GOES SAWBird LNA can work, although the difficult tracking requirements are still there so a smaller offset dish with custom helix feed might be preferred. Derek also provides useful tips, like the fact that the NOAA15 HRPT signal is quite a lot weaker than others.

Images from Dereks HRPT Guide

TechMinds: Testing the GA-450 Portable HF Active Loop Antenna

Over on the Techminds YouTube channel, Matt has uploaded his latest video which is a review of the GA-450 portable HF active loop antenna. The antenna costs between US$60-$80 + shipping and is available on Chinese market sites like Aliexpress and Banggood. It's advertised as covering 2.3 - 30 MHz, and uses a very portable and sturdy 20cm stainless steel loop. The active base amplifier is powered via a USB-C connector, and it even has a built in lithium battery for portable field use.

In his review Matt shows the antenna in action, noting that it's performance is quite a lot better than expected for it's small size, but it can't compare to his large half-wave end fed antenna. He notes that it appears to work best from 7 - 21 MHz, but not so well below 7 MHz. Overall he recommends it if you're looking for a small sized loop antenna.

GA-450 Portable Active Small Loop HF Antenna

Nils Reviews our RTL-SDR Blog L-Band Active Patch Antenna

Over on his blog Nils Schiffhauer (DK8OK) has recently uploaded a review of our RTL-SDR Blog Active L-Band Patch Antenna. This is a satellite patch antenna designed for experimenters who want to receive Inmarsat, Iridium, GPS and other GNSS signals. It covers 1525 - 1660 MHz. (Please note it does not cover GOES or other L-band weather satellites as these are much weaker signals that require a dish). The antenna comes as a set with mounting hardware and extension cable and can be purchased on our store for $49.95 including free worldwide shipping to most countries.

In his review Nils tests the patch antenna with his wideband BladeRF software defined radio showing a wide 60 MHz of bandwidth being received. He then goes on to show it being used to receive AERO, via the JAERO decoder, and STD-C via the Tekmanoid decoder.

We want to take this opportunity to pre-announce that due to rising shipping costs the price of this antenna set will be going up by $10 in early 2022. Before the price raise we will put out another post, but if you are interested in one we'd recommend picking one up soon.

Nils tests the water resistance of the antenna.

A RS41 and DFM09 Radiosonde Decoder Plugin for SDR++

A new decoder for RS41 and DFM09 radiosondes has been released as a plugin for SDR++ by dbDexter.  A radiosonde is a sensor package with RF transmitter that is attached to a weather balloon. Meteorological agencies around the world typically launch two per day in order to gather weather forecast data. With an RTL-SDR, appropriate antenna and a decoder it is possible to receive this data, and plot the GPS location on a map.

Installing a plugin for SDR++ requires adding the build options to the SDR++ source, and building SDR++, so it could be a little difficult for Windows, but relatively simple build instructions for Linux are provided in the Readme.

A Radiosonde Decoder for SDR++

Over on Twitter FelixTRG (@OK9UWU) has tested the plugin out and has found it to work well.

Multiband OpenWebRX Receiver via Multiple RTL-SDR Dongles

Thank you to Marko who has submitted his blog post showing how he's set up a multiband OpenWebRX receiver via multiple RTL-SDR dongles connected in server based network architecture. OpenWebRX is a open source software platform that allows users to set up multi-user network accessible RTL-SDR and other SDR receivers.

In his post Marko explains the architecture he's set up which consists of multiple antennas, and a Raspberry Pi running multiple RTL-SDRs right by each unique antenna. The Raspberry Pi's send the complete receiver bandwidth over the network to a more powerful virtual server running OpenWebRX. This architecture allows for scalability, and for many users to be able to connect at once.

Marco's Scalable OpenWebRX Architecture

The rest of Marko's post shows how he set up OpenWebRX and supporting software such as SoapyRemote, which handles the network transfer of the raw SDR data. Marko has created a YouTube video demonstrating multiple connections to the OpenWebRX server, and you can also try out his server directly via this link

An Raspbery Pi running multiple RTL-SDR dongles, sending raw data to the OpenWebRX server.

Guglielmo FM and DAB Receiver Software Updated to V0.3

Thank you to Marco Greco, author of Guglielmo for writing in and noting that v0.3 has now been released. Guglielmo is a Linux based RTL-SDR FM and DAB tuner software that supports SDRs including the RTL-SDR, Airspy, SDRplay, HackRF and LimeSDR. It is designed to be an easy to use program designed for media users, rather than hobbyist technical users. He notes:

In the last two releases I have substantially improved FM and RDS decoding and added support for MOT slides.

MOT slides allow DAB broadcasters to send JPEG or PNG images files over the DAB broadcast, and compatible receivers will display it.

A ready to use Appimage for Linux systems is availalble on the Github Releases page.

Guglielmo: Screenshot of the DAB Interface

Browser Based Weather Station Graphs via RTL-SDR, rtl_433 and Dash.plotly

Thank you to Gerrit Polder who has submitted his project where he has used an RTL-SDR and the rtl_433 decoder running on a Raspberry Pi, along with some custom software to create a browser based dashboard for his wireless weather station

Gerrit's weather station wirelessly displays data on a wirelessly connected LCD screen, but he notes how difficult it is to view historical data, or to graph trends. Having discovered that the rtl_433 RTL-SDR decoder supports his particular weather station (a Fine Offset Electronics WH1080/WH3080 compatible Weather Station (Alecto WS-4000)), Gerrit decided to write some code to log data to a SQL database, and display that data via a Python Dash.plotly web interface. The RTL-SDR, rtl_433 and custom software all run on a Raspberry Pi.

The interface allows Gerrit to view live and historical data all on neatly plotted graphs. HIs complete open source code can be found on Github.

Dash.pltly based weatherstation with data received by RTL-SDR and rtl_433