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Radio amateur activity
Meteor Scatter communications We explained in another page dealing with Impacts stories (in French) that when meteors enter into our atmosphere they heat by friction and disintegrate in ionizing gases in their vicinity. Their ionization trail has the property to reflect shortwaves, hence the interest that they represent as reflectors, replacing temporary the layers of the ionosphere, to name E- and D-layers located below 150 km aloft. Their density is close to 10000 electrons/cm3 but it is no more measurable at night. Historically to establish long-distance calls on shortwaves, in the years 1940-50 American soldiers tried to draw advantage of these ionization trails left by meteors to transmit aeronautical information such as the follow-up of convoys or radars information about ionospheric winds. Knowing their interest for experimentation, from 1953 radio amateurs were interested in this activity and today it is common to heard them working far european stations (in QSO) during a relatively long period of time during meteors showers. They are working "Meteor Scatter" or MS for short, also called "MBC" for Meteor Burst Communications. The radio communication can last from a few seconds (Pings) to several minutes (Bursts) while the signal strenght can vary from a few points above the background noise to several dozen of decibels above "59" if the bolid is particulary bright. Using meteors it is thus possible to establish long distance VHF contacts up to 2500 km away. The record is held on 144 MHz by GW4CQT (Wales) and UA6MA (Russia) in CW mode on August 12, 1977 with a distance of 3101 km between the two stations. Thank you electrons ! To check: IARU Region 1 VHF/UHF/SHF/EHF DX records The 6 m band (50 MHz) remains the best band to work because MS signals are the strongest and their duration is longer than on the 2 m band (144 MHz). However due to the wavelength used, directive antennas cut the 6m band are a bit more expensive than on 2m and not all HF or VHF transceivers are equipped with a 6m module. For these reasons it is thus not suprizing to find most MS amateurs on the 2m band. On 28 MHz burst are 25 times longer than on 144 MHz and the potential energy of signals is 120 times higher than on 144 MHz. On the other hand, on 432 MHz the same burst will be 10 times shorter than on 144 MHz and will be up to 30 times weaker. Procedure There is only one constraint : the International Amateur Radio Union, Region 1 regulation (Document BM27) defined that the portion of the band used for this kind of traffic is limited between 144.020 - 144.150 MHz in CW and 144.150 - 144.500 MHz in SSB. The standard procedure to establish a MS communication consists in either working in Sked or on Random. Sked consists in arranging a fix appointment on HF or VHF bands, either personally in establishing a QSO (long and tedious) or via the VHF European Net on 14.345 MHz or 28.345 MHz ±10 kHz on weekends and all the week preceeding main showers, between 11:00 and 14:00 UT. An ordinary QSO lasts less than 5 minutes in CW and about 1 minute in SSB. HSCW software to download : WinMSDSP from 9A4GL
Random consists in sending a general call "CQ Contact Meteor Scatter", or answering to a call on reserved frequencies to this mode of traffic. During main showers the duration is of one minute in CW and only 15 seconds in SSB. Taking into account the brevity of received signals (a "ping" should last over 1 sec to be useful), most amateurs work in Morse using a special procedure to establish a long distance MS contact. Usually the message is recorded on magnetic tape or digitalized and sent on the air at high speed CW (HSCW), between 10 and 1000 words/minute, (the record being of 3320 words/minute !), the correspondent decoding the information from his computer. For CWers interested in this mode, there is an excellent receive shareware ($20), WinMSDSP, that allows you to manage MS contacts in CW up to speed of 4000 words/minute. The Mteors Zenithal Hour Rate (ZHR) being highly variable depending the shower, the type of meteor (sporadic or not) and the time of the day, contacts are privileged during the periods of high ZHR. The three mains concerned showers are the ones of Quadrantids in January, Perseids in August and Geminids in December.
MS Traffic during Perseids occuring at mid-August. As the 6 and 2m bands are also crowed at that times, generating a lot of QRM, to work in SSB some amateurs prefer to record their message electronically and send it at speeds up to 1000 words/minute, the correspondent decoding the message at lower speed. Beside showers periods, the position of the meteors trail can also determine DX communications. The point in the sky from where the meteors seem to appear, called the radiant (where nothing happens but well around it), varies according to the observer latitude and it must be as low as possible if the amateur wants to try to establish a contact with a very distant station, located several thousands kilometers away from the transmitter. When you take an appointment, arrange you so that the direction of the shower is perpendicular to that of your correspondent to guarantee the success of your MS communication. As we explained in various files, in general summer months are the most favourable to ham activities because of the strong ionization of the ionosphere. Mid-August is also one of the best "MS season" with the recurrent apparition of the famous Perseid meteor shower. But do not try to work an MS station too early in the evening because most meteors hit the Earth after midnight. Indeed in the first hour of the morning and until dawn (say between 3 am and the sunrise), the eastern side of the Earth captures much more meteors that strike also the atmosphere at higher speed than on the opposite side where meteors have to catch up with Earth on its orbit to be visible. Therefore in the morning the meteors are more numerous, they are more bolids and their trail is also brighter than before midnight.
MS equipment Far from you the idea that you need high-tech material to work with Meteor Scatter. If you own a radio amateur license, what is mandatory for emission, you can purchase a small Yagi antenna constituted from 4 to 20 elements, horizontally polarized, offering a gain of a dozen decibels and a VHF transceiver of at least 100-150W PEP (if necessary with external VHF amplifier). Purists will say that they will prefer using an antenna offering the greatest aperture to be sure to cover the ionization trail, in crossed polarization, and offering a high gain, not to forget, but this is more expensive, 2x2 stacked antenna systems. If you already work in aurora, tropo and other weak-signal modes, you should be successful with HSCW MS without hardware modification. The duration of pings is relatively short but they can be numerous durant the few hours preceding the sunrrise. However, it has been estimated that during a meteors shower you gave a 5% chance of completing a contact in SSB, against 95% in HSCW. Most contacts are established either at distances of less than 800 km (500 miles) or over 2250 km (1400 miles) because of the heigth of the meteor trails, antenna characteristics, the scattering mechanism, etc. You ony need of a good location and a lot of power is you desire to work stations located over 2000 km away in HSCW.
Depending on meteor showers, the antenna must be raised in site as the radiant position moves according the sideral revolution. In the past a german equatorial mount offered a very appreciated way to track stars or any celestial object but at the computer age it is easier to install a Uni-Trac card in your PC (Kansas City Tracker is not more available) to drive an antenna rotator in azimuth and elevation ia the serial or USB port. In theory, for a better receive quality, the VHF head of the receiver must present a noise-figure ranging between 1 and 2 dB. The receiver must have an excellent frequency stability and provide an accurate frequency-meter better than 1 kHz. Today all solid-state equipments satisfy these specifications, and much more. Due to a slow shift in frequency mainly due to the Doppler effect, in order that messages be always readable, especially in CW at low speed, a RIT shifting the centre frequency up to 2 kHz will be welcome. At last, just like in radioastronomy, antenna preamplifiers will use low noise transistors and will be placed as close as possible to the antenna to reduce losses. At last the coaxial feeding the antenna will be less than 15 m long otherwhise a preamplifier will be mandatory to prevent signal attenuation. These specifications respect the usual recommendations we provide to any operator whishing to work on VHF. About the tape recording, select preferably a recorder which speeds are commutable in order to offer a broad bandwidth. Some, like the old UHER Report 4000 recorder are completely insulated against RF fields. At last, there are several beacons that you can listen to begin like "MS operator". They are ZB2VHF on 50.035 MHz, 5B4C5 on 50.490 MHz, LA3VHF on 144.880 MHz, DL0PR on 144.910 MHz and SK4MPI on 144.960 MHz. So, let you tempt by this activity during the holidays in becoming a Meteor Scatter specialist, a hunter of "New squares", DXCC and other QTH Locator ! Software MBC/MS to download: Colorgramme WMeteor - HROFFT2RMOB The echo of bolids During main meteors showers radios and TV signals are constantly disturbed by ionization trails. These echoes can be heard all over the world listening to power radars and AM/FM transmitters. One of the most powerful transmitting stations is located in the base of Kickapoo, Texas : NAVSPASUR, acronym of Navy Space Surveillance Radar. Its power is 800 kW continuous (CW). The transmitting antenna is directed in a E-O direction and is tuned on the frequency of 216.98 MHz. Its principal mission consists in tracking satellites and their fragments for the US Strategic Command. Between 1958 and 2004 we launched 20000 tons of materials in orbit and currently 25500 objects are orbiting around the Earth, among which 700 are operational satellites representing a mass of 4500 tons. One day they they will fall down on Earth. Although meteors measure less than 1 mm and are in general too small to be detected, their ionization trail produces a strong echo that can be heard with radio amateur receiver. In 1998, Steven Bienvenu, who is also an amateur radio, worked at NAVSPASUR during the night of Leonids and Geminids and recorded at this occasion some meteors echoes. The signals of meteors, satellites and spaceships have distinctive signatures that dynamic spectrum analyzers equipping NAVSPASUR radars can identify. Dynamics of the signal
The signal of a meteor is distinguished easily from that of a satellite by its duration. A satellite echo is usually very short and sounds like "blips" or "pings" like those emitted by radars and sonars. In addition a satellite moves relatively slowly compared with a meteor : between 1 and 10 km/s according its orbit. As a satellite moves quickly in front of the antennas, and as the orientation of its the flight path vector changes compared to the radar position, the Doppler shift is accentuated, changing slowly the signal frequency from the short to the longer wavelengths. The ionization trail left behind a meteor moves at a speed of about 0.02 km/s (72 km/h), whereas the meteor itself moves between 12 and 72 km/s on its orbit. There is thus no Doppler effect in the meteor echo. For this reason its echo on a spectrum analyzer traces usually a horizontal line which does not shift gradually in frequency with time like it should do if the echo was reflected by an airplane. The echo of a meteor is on the other hand very long. They last a few seconds in general but certain echoes can exceptionally persist more than 10 minutes, and in extremely rare cases, persist one hour ! The signal looks to blips but with chirps and whistles a bit like the sound of lightnings that propagates in the ionosphere, which an example is presented below.
These meteors echoes can be captured at frequencies ranging between 40 and 100 MHz due to the fact that ionized trails are better reflected under 100 MHz, where are emitted the typical meteors low frequency signals. The frequency of 217 MHz used by the NAVSPASUR radar is also appropriate. Amateurs can capture the echoes of NAVSPASUR at the condition to live on the US territory or in the Caribbean region. Beyond this area VHF antennas are useless (their range is less than about 3000 km). The other solution is installing his own receive station. Receive equipment It is quite easy for an amateur to build a receiving MS installation. As explained on the NASA website, at home Bienvenu uses a simple receiver ICOM R7000 in USB mode centered on the frequency of 216.980 MHz with a small offset to center the signal of the NAVSPASUR in a narrow bandwidth of 2.5 kHz. The antenna is an ordinary TV/FM Yagi. During meteors showers the antenna is pointed towards the azimuth 275° (Western) in direction of the transmitter of the NAVSPASUR located in Louisiana, the nearest site in straight line. Knowing that a meteor trail appears around 80 km aloft, Bienvenu points his Yagi just 8° above the horizon to be sure to be aligned with the return echo reflected by the ionisation trail. Audio signals are recorded with a sampling of 11 kHz (11000 samplers/sec) thanks to a sound card installed in a Pentium computer running at 120 MHz. Of course with the development of DRM (digital radio), you can take advantage of receive cards like models sold by WinRadio, most of them covering HF and V/UHF bands. These cards are as performing as a classic receiver. This manufactuer also sells a short multi-band antenna. There are also cheaper solutions like using a SDR device. Most are not larger than a USB stick. As explained Jean-Louis Rault, F6AGR, we can also use the VLF band (0.1-10 kHz) with a whip or a loop antenna connected to a digital recorded like ZOOM H2. Of course, in all cases the receiver must be connected to an external VHF antenna. (requires an active Internet connection)
On his side, Stephen McGreevy, N6NKS, sells two ELF/VLF receivers and a whip antenna able to record signals emitted by aurora as well as the activity of meteors and thunders. Note that since an ELF receiver (3 Hz - 3 kHz) is very sensitive in the 50-60 Hz range, it must be used away from the electricity grid (several kilometers away from any electrical line or HV transformer) or it will capture a continuous buzz (hum), a condition impossible to meet in urbanized and even sometimes rural areas where there are high voltage lines and transformers every kilometer. In addition, such a receiver also sensitive to signals emitted by all low-frequency transmitters such as computer screens, a portable recorder (e.g. ZOOM H2) or a cell phone. This activity has proved its utility in counting meteors hard to see visually, those appearing during the full Moon or which appear at daytime. In this way Meteor Scatter communications allow radio amateurs fan of astonomy to extend their activity beyond the usual QSOs. If you are tired to work outside in winter, listen rather meteors at warm close to your radio ! Fore more information The sound of meteors (on this site) Listen live to Meteors (requires an active Internet connection) W8WN, High Speed Meteor Scatter Forward Scatter Meteor Radar, NASA/MSFC Radio Meteor (where you will find Meteor and Cologramme WMeteor software) On the potential meteors ELF/VLF radiations, Jean-Louis Rault, F6AGR ELF/VLF receivers, Stephen McGreevy, N6NKS Meteor Observation at the Observatory of the University of Ghent (B) Meteor Scatter Graves Radar, Florent Labelle (F) The American Meteor Society Radiometeor Project Perseid Below - ISS Expedition 28, 13 Aug.2011, APOD JAS, Jordanian Astronomical Society Detection software from Ilkka Yrjola, OH5IY WinMSDSP (High speed CW program for MS by 9A4GL) RIGPIX (hardware database) WinRadio.. |
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