Observing Meteors by Radio

JAS has recently started observing meteors by radio, ten trials were done until we successfully observed meteors by radio, the first eight trials were done in Amman (The capital of Jordan) in which the israeli radio stations affected our observations, and thus we held the 9th trial in Sahab City (20 km away from Amman), and we succeeded in observing one meteor only. However, the israeli station was still annoying ! So we decided to move to the desert, specifically in Al-Azraq desert (80 km away from Amman), and so on 7 September 1998 we went to the desert. During the first hours we just did some experiments for observing meteors by radio. Later on, after we were sure that every thing was going fine we started seriously observing on 8 September 1998 at 1:44 am (local time), and the observations lasted till 6 am (local time), with an effective observing time of 3 hours exactly, at which we observed 173 meteors by radio. The observers were:-

• Moh'd Alawneh
• Moh'd Odeh
• Tareq Katbeh

When a meteoroid enters the atmosphere, the particle will completely ionize its trail at an altitude that ranges between 120 km and 80 km, and the ionized trails are capable of reflecting radio signals from terrestrial stations, which include those broadcast by commercial FM and TV stations. The advantage of of this kind of observation that it can be done in daylight and during cloudy or rainy weather ! Also the moon's light is no more annoying when observing meteors by radio. Radio detection rates of meteors tend to be higher than visual observation rates. This occurs because particles down to 10^-5 kg can be detected visually, while particles down to 10^-10 kg can be detected by radio. Assuming a density of 1 t/m³, these mass limits correspond to diameter of about 3 mm and 0.06 mm, respectively. By radio observation you can detect meteors down to 8th magnitude !

The easiest way to observe meteors by radio is to use commercial FM radio (preferable digital), and attach it to an antenna (preferable FM Yagi antenna), then try to find an empty frequency from 87.5-108.0 MHz, where you do not hear any kind of music or talking, and is being used by a distant transmitter (mostly a distant FM radio station) about 300-2000 km away from your location of observation (preferably 500-800 km). It is better to choose a station that transmits over 30 kilowatts, and point the antenna towards the station. Now, all what you hear is a continuous static, and when a meteor passes and if its position is suitable then it will reflect the waves of the distant station and you will hear it, the period varies from 0.1 second to several seconds or even minutes (mostly on the order of 0.25 second). They are small segments of what is being transmitted. They sound like bumps, thumps and chirps. The longer signals are recognizable pieces of music or talking. To distinguish the signals reflected from a meteor than others such as aeroplanes, the signals reflected from a meteor is very sudden, mostly loud and clear, and end gradually.

Below are the results achieved during our first experiment in observing meteors by radio in the 21st Astronomical camp dedicated to observe meteors by radio, 173 meteors were observed in three hours.

• Observers: Moh'd Alawneh, Moh'd Odeh, and Tareq Katbeh
• Location: Al-Azraq desert, Jordan (37 07' E, 31 43' N)
• Frequency: 97.2 MHz
• Transmitter Location: Three stations from Turkey, (750 Km, 900 Km, and 1106 Km), 30 KW Power.
• Antenna: Yagi FM 3 elements.
• Receiver: Commercial FM radio (Eroica).
• Observing Method: Listening by ear.

• Q1) Is it necessary to use a digital radio ?
• Answer: It is highly recommended to use a digital radio, since the radio will be tuned to a frequency of a distant transmitter that you don't hear anything but a continuous static, and if a meteor passes in the right place in the sky, you will briefly hear the signal from a distant FM station for a while. The signal may be so short that all you hear is a brief "ping". Or you may hear several words or music. Consequently, how will you be sure that you are on the desired frequency if you are not using a digital radio ! However, if you are accurate enough, you may success in using an ordinary analog radio.
• Q2) Which frequency to choose ?
• Answer: Always do your best to choose the lowest frequency, since the lower the frequency the more meteors you hear, also the same meteor will produce longer duration and stronger reflection at the lower frequencies. If there are more than one low-frequency station, and all are transmitting from the desired direction, then choose the one with the highest power.
• Q3) From where can I get the frequencies of distant transmitters ?
• Answer: The best way we found is to look at the atlas to know which countries are included in your range (300 - 2000 Km), then you may search for the Fax or E-mail of the radio corporations in these countries, ask them to provide you of the FM frequencies that they transmit 24 hours a day, and it is preferable to ask about their locations and power. Also, mostly you can find these data already in their home page if they have one. I was able to get the FM frequencies of Kuwait and Egypt from the internet, while TRT in Turkey sent me a Fax of about 30 FM stations transmitting from Turkey 24 hours a days, and have a power of 30 KW.
• Q4) Can I use an ordinary antenna ?
• Answer: Yes, an indoor antenna can do the job, or even a car radio. But for sure the Yagi antenna picks more meteors and gives the best results.
• Q5) Where to point the antenna ?
• Answer: The most common method is to point the antenna horizontally towards the distant transmitter, and sometimes you might find it better to give the antenna a certain angle, which would prevent direct reception from local stations. If you are observing sporadic meteors, then it does not matter where to point your antenna, but it seems more useful if you point your antenna South in the early morning hours and listen for signals as Earth sweeps up meteoroids in its path. While if you are observing a meteor shower, then the antenna should be perpendicular to the radiant. Having in mind that in either case the antenna must be pointed towards the distant transmitter too.
• Q6) Does the number of meteors vary during the day ?
• Answer: Speaking about sporadic meteors, the maximum hourly rate occurs at nearly 6 AM local time, and the minimum at 6 PM. The ratio likely to be something like 4:1. As for meteor showers, the best results will be obtained when the radiant is between 30 and 60 degrees above the horizon, and the optimum position is 45 degrees.
• Q7) If there are two observers at the same time, will they detect the same number of meteors ?
• Answer: Number of meteors detected strongly depends on your equipment, frequency, location, time of observation, and atmospheric conditions. So any difference in the above points, may produce totally different results.

* References:-

• Zay's Meteor Observing GuideBook, by George Zay.
• Observer's HandBook, of the Royal Astronomical Society of Canada (RASC).
• Special thanks are to people who assisted us in this subject, such as: Eng. Hisham Shahin (Jordan Radio & Television Corp.), Mr. Moh'd Sayyah (National Petroleum Company), Jordanian Security Forces, Dr. Ahmad al-Tamimi, Eng. Ibrahim Faza', Eng. Abdullah al-Rimawi, Mr. Saleh Al-Saab (Saudi Arabia), Mr. Christian Steyaert (Belgium), Mr. George Zay (USA).