The first meteor scatter experiments date back to the 1930s through the use of active radar techniques - this is what we say when the observer sends a radio signal directly into space to receive back its reflections; however, this is generally not the case for those who practice this activity at an amateur level, as it requires the preparation of a real customized radar (although there are exceptions such as the BRAMS project).

The alternative consists in only receiving the signals generated by third parties and reflected towards the ground by the meteors and their ionized trails. In this case we speak of passive radar techniques, which are much more within the reach of amateurs, since they require a radio receiver, the relative antenna for the band on which one intends to operate (compatibly with the legislation in force in the country in which you operate) and a computer for data recording and representation.

The classic setup includes an analog receiver, set in SSB or CW mode, whose audio output is collected from a PC sound card, MIC or LINE input. We can briefly call it AAD setup (analogue radio + analog / digital acquisition). It was my first setup when I started with this activity in 2014, but I abandoned it immediately because I was never able to receive anything; perhaps due to my inexperience , maybe because the second hand receiver I bought - a MVT-7100 - was defected, maybe because the antenna was not well placed, I don't know. Probably a mix of all these reasons, as many people is using this setup successfully.

The fact is that to capture my first echo I needed to switch from an analog receiver to a digital one, also known as SDR, more precisely an RTL-SDR a very entry-level one.

Terratec DVB-T Terratec RTL2832U-based DVB-T dongle (Tuner: E4000)

This type of receiver derives from DVB-T dongles for receiving digital terrestrial TV based on the Realtek RTL2832U chipset, using an alternative driver to the one normally distributed along with dongles for viewing TV programs.

This alternative driver, by Antti Palosaari, Eric Fry and Osmocom (2012) allows direct access to the I/Q data of the radio signal acquired by the TV tuner contained in the chip. This has allowed the development of various software that use the DVB-T stick as a broadband digital radio. The following years saw several receivers derived from DVB-T dongles come onto the market, with the same chipset and more refined circuitry, intended to be used primarily as broadband radio receivers.

In my case it was still a DVB-T inserted in the same PC used for the signal acquisition. I was using HDSDR software to receive the radio signal. In the presence of a meteoric echo, the radio signal, demodulated in SSB or CW, produced the characteristic whistle-like sound. This sound came out of the headphone jack and back into the microphone jack. With a second program - Spectrum Lab - I generated the audio spectrum and detected the peaks by taking screenshots. It was therefore a DAD setup (digital radio + analog/digital acquisition).

However, I completed this setup later. In fact, I detected the first echo using only the HDSDR radio and standing in front of the PC waiting to hear a ping and to see something interesting on the spectrum. This happened on October 19, 2014, giving as result the picture below:

first capture My first radio echo captured

The radio signal used as a source was the same one I use today, the GRAVES, a French military radar located in Dijon which monitors space debris transiting over central-southern Europe by transmitting its carrier on 143.050 kHz.

With this setup I recorded discontinuously, keeping the receiver on only during periods affected by known meteor showers such as the Geminids, Quadrantids, Perseids, and Leonids. This was because I was using my home laptop: energy intensive, dated and noisy. At the end of each swarm I stopped the system, loaded the accounts into an Excel sheet and generated the graph of the daily accounts.

I then wrote about this experience (in Italian) on GABB website while the collected audio spectra have been included in the GABB Facebook page photo albums, of which the following screenshot a sample.
meteor SpectrumLab screenshot of a Quadrantid's echo, January 2015

Note that unlike the previous screenshot, which shows HDSDR, this spectrum has been generated with SpectrumLab.

Starting from 2016 - if you look at the albums on Facebook - you will see that the adopted software changes, it is no longer SpectrumLab. These are the first versions of Echoes, the program that I started developing in 2015.
lyrids 2016
Echoes 0.1 screenshot under Lyrids meteor shower 2016

Those who have already had the opportunity to use Echoes may not immediately recognize it, since from 2015 to 2018 - the year in which I published the project on (version 0.18) thus becoming an open source project - the appearance of the interface has undergone several changes.

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