In the autumn of 2024, Iolanda Ferro installed a small Yagi antenna on the south wall of her observatory shed outside Naples and pointed it at the GRAVES space-surveillance radar in eastern France. Within a week she was detecting meteors during her morning coffee.
Radio meteor detection is, for the amateur with modest electronics skills, one of the most rewarding and least appreciated branches of meteor astronomy. The technique works in cloud, in daylight, and through the worst urban light pollution.
It also works while the observer is asleep, eating breakfast, or out of the house. The receiver records, the software counts, and the results are available in the morning.
The physics is straightforward. A meteor entering the atmosphere creates a brief column of ionised gas at altitudes between eighty and one hundred kilometres. This column reflects radio waves much as a thin layer of mercury reflects light.
A radio transmitter and a radio receiver, positioned with the meteor's ionised column between them, can therefore detect the meteor's passage as a brief enhancement of the transmitted signal. The technique is called forward-scatter meteor detection.
The amateur does not need to provide the transmitter. Several powerful continuous transmitters operate in convenient frequency bands and serve, by accident, as ideal beacons for amateur meteor detection.
The most widely used in Europe is GRAVES, a French Air Force space-surveillance radar operating at 143.050 MHz from a site near Dijon. The American equivalents include various VHF television transmitters and some forms of FM radio.
Ferro's setup consists of a three-element Yagi antenna tuned to 143 MHz, a low-noise amplifier, a software-defined radio dongle, and a laptop running open-source spectrogram software. The total cost, in 2024 euros, was approximately two hundred and ten.
The antenna is the part most amateurs underestimate. A good 143 MHz Yagi is approximately two metres long and must be pointed in the general direction of GRAVES — for Ferro, roughly northwest, at a moderate elevation.
The software, Spectrum Lab or a similar package, displays the received signal as a waterfall plot. A meteor appears as a brief bright streak in the otherwise quiet band, lasting anywhere from a tenth of a second to several seconds.
Bright meteors and fireballs produce longer reflections, sometimes lasting tens of seconds, as the ionised column persists in the upper atmosphere and is gradually dispersed by high-altitude winds.
Ferro's typical daily count, integrated over twenty-four hours, runs between fifty and one hundred and fifty meteors in quiet periods and between three hundred and two thousand during major showers.
The August 2025 Perseid maximum produced a peak hourly rate of one hundred and ninety-three radio meteors during the most active hours, with a daily total exceeding two thousand four hundred over the three-day peak.
Compare this with her optical count from the same maximum — seventy-three meteors in two hours from the olive grove. The radio receiver, running unattended through cloud, fog, and daylight, recorded a substantially larger and more complete picture of the shower's actual activity.
The radio technique is particularly valuable for the daytime showers. The Arietids, peaking in early June, are one of the strongest annual showers but are almost entirely invisible to optical observers because the radiant is too close to the sun.
Ferro's radio receiver picks up the Arietids reliably each year. In June 2025 she recorded peak hourly rates above seventy from a shower that no Italian optical observer saw a single meteor of.
The data is also useful. The British Astronomical Association and the IMO both accept radio meteor counts in their global databases, and several long-running amateur radio meteor stations provide some of the most consistent datasets in the discipline.
There are, Ferro notes, two persistent problems with the radio technique. The first is interference from local electronics — LED street lights, switching power supplies, and digital television have all degraded the radio environment for amateur work over the last decade.
The second is the difficulty of distinguishing meteor reflections from aircraft reflections at low elevations. An aircraft passing through the GRAVES beam produces a long, slowly drifting trace that can be confused with a long-duration meteor by inexperienced observers and by poorly tuned software.
Ferro's recommendation, for the amateur considering a first radio meteor station, is to start with the smallest reasonable antenna, the cheapest reasonable SDR, and the free Spectrum Lab software. The investment is modest, the learning curve is steep but finite, and the reward — meteor counts in daylight, through cloud, while the observer is at work — is something the optical observer cannot match.
She closes her column with the observation that the radio receiver, humming quietly in the corner of her shed, has detected several meteors per hour, every hour, for the last fourteen months without interruption. The sky, she reminds her readers, is never empty.
