Category: Applications

Building a 3D Printed LHCP Helical L-Band Feed for Inmarsat, AERO and HRPT

Thanks to Manuel a.k.a. Tysonpower for submitting his latest YouTube video tutorial about building an 1550 MHz L-band LHCP helical antenna for receiving satellite signals such as Inmarsat, AERO and HRPT.

Manuel's design is based on a 3D printed part which is used to accurately form the helical winding. The winding then mounts onto an aluminum plate and a satellite dish arm using a custom 3D printed adapter for the dish arm. In the video he uses the helical feed with an 80cm satellite dish and a standard 40mm LNB mount on the dish arm. Attached to the feed are two LNAs in series which help to lower the noise figure and reduce losses in the coax cable.

With this setup he writes that he was able to get very good AERO and Outernet reception from Alphasat (25E geostationary). He also writes that he's had good results using it for HRPT reception as well.

The 3D printing STL files and list of parts required are available on Thingiverse, and the companion video is shown below. Note that the video is narrated in German, but English subtitles are available.

[EN subs] LHCP Helix L-Band Feed - 3D Druck für eine genaue Helix

Manuel's L-Band Helical Feed
Manuel's L-Band Helical Feed

QrssPiG: Decoding QRSS on a Raspberry Pi with an RTL-SDR

QRSS is a ham communications mode that is essentially just very slow CW (morse code), with each dash/dot being broadcast for a number of seconds. With QRSS instead of audibly decoding the morse code signal, it is decoded visually via a spectrum display (or automatically by software). It is designed to be a QRP mode, which means that hams transmitting QRSS can be heard all over the world even though very low transmit power is used. 

QrssPiG is a QRSS grabber program that runs headless on a Raspberry Pi and can interface with an RTL-SDR. It automatically generates the waterfall graphs of received QRSS images, and supports uploading them via SCP or FTP. The software can also run with a HackRF, or via audio piping from another SDR or standard hardware radio.

Recently on Twitter @ON4CDJ has been trying QrssPiG with an RTL-SDR V3 and has been having good results.

SDR Programming For Kids: LimeSDR Mini with Scratch on a Raspberry Pi 3

Scratch is a visual block based programming language aimed at getting kids into programming. Recently the LimeSDR team have been working at creating a Scratch interface for their LimeSDR Mini. It is basically working as a wrapper/interface to the processing backend which is handled by LuaRadio.

The idea is to keep the barrier of entry to SDR as low as possible, by making SDR programming accessible to kids as well. The software is currently a work in progress, but they write that they are attempting to develop the Scratch blocks necessary to enable the transmission and reception of text messages. Something like that would make a great learning tool for educators.

The video demo shows Scratch and the LimeSDR running on a Raspberry Pi 3. During the demo he creates a simple 433 MHz spectrum display by connecting up several blocks.

Scratch running with a LimeSDR Mini on a Raspberry Pi
Scratch running with a LimeSDR Mini on a Raspberry Pi

QRadioLink Development Webpage Now Up

Back in September we posted [1, 2] about the QRadioLink software which is an RTL-SDR compatible digital amateur radio voice decoder and encoder program for Linux and Android (with chroot). It supports modern digital voice codecs like Codec2 and Opus. It is capable of being used with multiple SDRs, and can be used for transmitting digital voice too if you have a transmit capable SDR.

Andrian the developer recently wrote in to let us know that QRadioLink now has a website at qradiolink.org that you can follow for updates about its development. The website also explains some of the features of the software, and lists possible performance values of digital voice. The features include:

  • Receives and transmits analog voice, digital voice, low resolution video, text, IP protocol.
  • Narrow band modem with Codec2 or wideband modem and Opus.
  • Digital Modems: BPSKQPSK2FSK4FSK
  • Modes: narrow FM, SSB, digital voice, digital video, digital data
  • Formats: Codec2 700B, Codec2 1400, Opus 10 kbit/s
  • Video formats: JPEG
  • Supported hardware: Ettus USRP, RTL-SDR, HackRF, BladeRF and in general all devices supported by gr-osmosdr

Typical Receiver performance is given in the following table, with all values being measured on an R820T RTL-SDR.

Mode Condition Sensitivity (dBm)
Codec2 700B 20 db SINAD -115
Codec2 1400 20 db SINAD -112
Opus 20 db SINAD -102
Narrow FM 12 db SINAD -118

In the future Adrian hopes to expand the software to include features like VOIP integration, SSB transceiver, DTMF & CTCSS encoder/decoders, multi-channel RX, HD video, remote control and a GUI improvement.

QRadioLink Main Page

Building your Own Cell Phone Network with a Raspberry Pi and BladeRF

As part of their senior project Matthew May & Brendan Harlow of Champlain College worked on a project that involved creating their own software defined radio based portable cell phone network. If you're interested their setup is nicely documented on their project page. Basically it consists of a bladeRF software defined radio and Raspberry Pi running the YateBTS base station software. This is nothing new in terms of work done before, but the clear documentation makes it a good starting point for anyone looking at building their own SDR based cell basestation. 

A custom cell basestation may be useful for those in remote areas without commercial cell phone reception, during disasters or even just to create a type of secondary network in your home.

[Also seen on Hackaday and Motherboard]

A cell phone connected to their custom network
A cell phone connected to their custom network

Testing a 16x RTL-SDR V3 WebSDR System for the Satcom Band

Over on Twitter Denis (@uhfsatcom) has recently been teasing us with photos of his 16 dongle RTL-SDR V3 setup. The system looks like it's designed to be a satcom band WebSDR receiver. 

The satcom band is around 240 - 270 MHz and mostly consists of various military satellites that act as simple repeaters which are often hijacked by pirates. WebSDR is a piece of software that allows for online web streaming of SDR radios. Users from all over the world can listen in if made public. Denis has also uploaded a short video showing a test of 8 dongles running and receiving the satcom band on his WebSDR system.

We look forward to hearing more updates on this project!

8 rtlsdr websdr test

RadioForEveryone New Posts: Antenna Weatherproofing, NooElec Nano 3 Review, ADS-B Antenna Shootout

Over on his blog 'Radio for Everyone' author Akos has uploaded three new posts. The first shows how to cheaply weatherproof antenna connections by wrapping electrical/plumbing tape around the connection. He shows and example with the FlightAware ADS-B antenna.

The second post is a review of the relatively new NooElec Nano 3, which is a small form factor RTL-SDR that comes with a TCXO and metal case. Akos shows how the form factor is good for using it with Mobile phones. Akos opens the unit up and shows us how the unit is sandwiched inside the metal case with two thermal pads for improved heat dissipation. Later in the review he also discusses the MCX connector, TCXO and heat.

The third post compares three commercially sold antennas at ADS-B reception. The compared antennas are the FlightAware ($45) and Jetvision ($90) ADS-B antennas as well as our RTL-SDR Blog general purpose dipole ($10). The results show that the Jetvision antenna performs the best followed by the FlightAware and then the dipole. However we note that Akos has incorrectly used the dipole as he did not orient it as a vertical dipole.

Radio For Everyone: Nano 3 Size Comparison
Radio For Everyone: Nano 3 Size Comparison

Meteor Logger: A Tool for Counting Meteor Detections with an RTL-SDR

Thanks to Wolfgang Kaufmann for submitting news about his new software called ‘Meteor Logger’. This tool can be used to count the number of meteors entering the atmosphere which have been detected by a meteor scatter setup using an RTL-SDR or similar SDR.

Wolfgang writes about his software:

I have developed a new piece of software “Meteor Logger” to detect and log radio meteors from the digital audio stream of a PC-soundcard. It is based on Python 3. It is addressed to those meteor enthusiasts who want get the most information out of forward scattering of radio waves off meteor trails. “Meteor Logger” do not display spectrograms, it delivers an instantaneous and continuous numerical output of the detected signal with a high time resolution of about 11 ms. Thereby a radio meteor signal is not detected on the basis of an amplitude threshold but on its signature in the frequency domain. “Meteor Logger” has a built in auto notch function that may be helpful in case of a persistent strong interference line. From these data not only hourly count rates can be derived but it is also possible to easily study power profiles of meteors as well as Doppler shifts of head echoes.

As receiving front end a RTL-SDR is fine, if you strive after a very high signal resolution you may use a Funcube Dongle Pro. I employed SDR# to run the RTL-SDR. GRAVES-radar is used as transmitter. The added screenshot shows this setup together with “Meteor Logger”.

Additionally I wrote an also Python 3 based post processing software “Process Data” that allows for clearing the raw data, viewing and analysing them and exporting them in different ways (e.g. as RMOB-file for opening with “Cologramme Lab” of Pierre Terrier, see added screenshot).

Everything else you may find on my website http://www.ars-electromagnetica.de/robs/download.html

Meteor Logger
Meteor Logger

Meteor scatter works by receiving a distant but powerful transmitter via reflections off the trails of ionized air that meteors leave behind when they enter the atmosphere. Normally the transmitter would be too far away to receive, but if its able to bounce off the ionized trail in the sky it can reach far over the horizon to your receiver. Typically powerful broadcast FM radio stations, analog TV, and radar signals at around 140 MHz are used. Some amateur radio enthusiasts also use this phenomena as a long range VHF communications tool with their own transmitted signals. See the website www.livemeteors.com for a livestream of a permanently set up RTL-SDR meteor detector.