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<H1>CHAPTER 5:<BR>OBSERVING TECHNIQUE - RADIO</H1>Contributed By: George Zay,
IMO Member
<P><IMG src="Chapter 5_files/bar.gif">
<P>Currently, monitoring radio meteor activity is beyond the scope of NAMN. But
to those who wish to investigate it, the following should prove to be a start.
<P><B>A. BACKGROUND</B><BR>Monitoring meteor activity by radio got its start
right after World War II. It was then found out that meteors could reflect radio
signals. There are two ways that radio meteors can be detected. One is known as
back scatter. This is monitoring with radar equipment and is mostly in the realm
of professional work. A simpler method, and one that amateurs can participate
in, is forward scatter.
<P>It has been learned that when a meteoroid enters the atmosphere, it produces
an ionized column of gas molecules. This ionized gas has the ability to reflect
radio signals between a transmitter and a distant receiver. The frequency range
that this occurs at is between 40 and 150 MHz. Although the optimum lies between
40 and 70 MHz, the common FM band is frequently used for back scatter work. This
FM band is between 88 and 108 MHz.
<P>The technique used to register forward scatter meteors is actually quite
simple. A receiver is tuned to a distant radio station that is located below the
observer's horizon. The distance between the receiver and transmitter varies
from between 200 and 1000 miles. Most often a commercial radio station is used
as a transmitter. Aircraft ground beacons are also suitable transmitters. The
station may not be heard, usually only background noise is apparent. At the
moment a meteor appears at the correct angle, there is a short contact (usually
0.1 to 4 seconds) with that radio station. For larger meteors, it is possible to
have longer lasting signals, often up to minutes in duration. This contact gives
itself away as a signal increase in a piece of music, voice or noise. Since this
technique uses electromagnetic waves, it can be used during the daytime, when
there is a bright moon, or during cloudy and rainy weather. Therefore, this
method is ideal for continuous periods of observing.
<P><B>B. EQUIPMENT</B><BR>The best FM radio to use is one that is digital and
that has a shielded cable connection where the antenna plugs in. The digital
type of radio is easier to set on the desired frequency. A Yagi style FM radio
antenna is also required (at the time this was written, Radio Shack sold
suitable antennas for about $16 and local TV antenna companies sell a more
directional FM radio antenna for about $150). Unfortunately, which type of
antenna to use depends on trial and error. It would probably be best to try the
lower cost antenna first. Assuming that this type is used, hook up the antenna
to the radio with a coax cable.
<P><B>C. FINDING A MONITORING FREQUENCY</B><BR>To find a frequency, try them one
at a time from 88.0 MHz to 108.0 MHz. Write down all the frequencies where there
is no music or talking. All that should be audible is static noise. Be sure to
turn the antenna all the way around (360 degrees) to find this static area. Do
not direct the antenna very high, because in most places in the United States,
the antenna may receive unwanted, continuous reception.
<P>If you're lucky, you'll find several or more frequencies where nothing but
static is heard. These are the potential useable frequencies. For those who are
unable to find any, there are two options. Move your radio equipment to another
location, preferably in a valley and many miles away from the city (30 or more).
Another alternative is to buy the more expensive, more directional, and most
likely, larger (12 foot long antenna), and try all the frequencies again. If the
directional antenna still doesn't work, try another location and/or consider a
different frequency band.
<P>On useable frequencies, it is probable someone is transmitting on it at least
200 to 1000 miles away, but at an unknown direction. The only way to determine
the direction is to go to the local library and find a book that lists frequency
and station locations. If the library doesn't have such a book, it may be
possible to find it by looking in the phone books of different cities located
within 200 to 1000 miles. Ideally, choose a station that transmits over 30
kilowatts and is located about 300 to 500 miles away.
<P><B>D. SETTING UP</B><BR>Next, find your location and the location of the
transmitting station on a suitable map. Taking geographical north as being 0
degrees, find what degree angle the transmitting station is in relation to the
observing location. This is the transmitting station's azimuth.
<P>Then, with your antenna pole at the middle, use a compass to find true north.
Be sure to do this with the pole and other metal out of the way or a false
reading will result. Turn the antenna to point toward the transmitting station.
Using a protractor, tilt your antenna so that it points up at a 45 degree angle
instead of the traditional horizontal angle.
<P><B>E. OPERATION</B><BR>Now, just listen to all the static. When a meteor
passes by, it may or may not (depending on the angle among other things),
produce a signal. The radio can detect meteoroids down to 8th magnitude at
least, with most being very short signals on the order of 1/4 second. They are
actually small segments of what's being transmitted. They sound like bumps,
thumps and chirps. The longer signals will register as pieces of music or
talking. These are usually very sudden, loud and clear, and will begin and end
abruptly. Aircraft can interfere when they fly nearby, but they usually produce
signals which are gradual before getting real loud.
<P>During observations, it is advisable to use one frequency exclusively with
the antenna always pointed in the same direction and at the same elevation. This
way, day to day monitoring establishes a reliable pattern that can be compared.
On average, expect to hear the least amount of meteor activity around 6 pm local
time and the greatest activity around 6 am local time. A typical hourly rate
around 6 pm is about 7, while at 6 am it may increase to about 60 or so. Of
course, a major meteor shower could change these rates.
<P><B>F. RECORDING</B><BR>One recording method is to purchase a small hand
counter and simply press the button for each signal heard, regardless of their
duration. If the signal is 1 second or longer, note them separately on paper. Do
this for half hour increments during each observing hour.
<P>Interpret signals lasting more than 5 seconds in duration as being most
likely caused by a visually bright meteor. It appears that longer signals are
produced by brighter meteors (-1 magnitude and up) rather than fainter ones.
Also, it's been noted from some observers that signal durations tend to differ
from frequency to frequency. Signal durations tend to not be as long at the FM
band level as they are with frequencies near 50 MHz. Try to observe visually
with a speaker close by. Sometimes, it's possible to get simultaneous events
which can be noted both visually and by radio.
<P><B>G. WHEN TO LISTEN</B><BR>Actually, it is possible to listen for meteors
any time of the day or night. Generally, the most active 12 hour period is from
midnight to noon. Major shower activity usually produce exceptionally high
hourly rates both audibly and visually. The radio can quickly become so
saturated with radio reflections that it produces continuous radio reception. At
this point, it's almost useless to maintain hourly rates. But fortunately, these
moments are exceptions to the rule. Observing periods will have the greatest
scientific benefit if they are carried out in one hour increments. Periods
shorter than this become unreliable.
<P>There are meteor showers that are almost exclusively monitored by radio.
These are known as the daytime showers and usually peak shortly after sunrise.
The IMO's list of daytime showers include:
<P>
<CENTER>
<TABLE border=5 cellPadding=2 cellSpacing=4>
<TBODY>
<TR>
<TH align=middle>Meteor Shower</TH>
<TH align=middle>Peak</TH>
<TH align=middle>ZHR</TH></TR>
<TR>
<TD align=middle>Cap/Sagittarids</TD>
<TD align=middle>Feb. 1</TD>
<TD align=middle>15</TD></TR>
<TR>
<TD align=middle>Chi Capricornids</TD>
<TD align=middle>Feb. 13</TD>
<TD align=middle>5</TD></TR>
<TR>
<TD align=middle>Piscids</TD>
<TD align=middle>Apr. 2</TD>
<TD align=middle>--</TD></TR>
<TR>
<TD align=middle>Delta Piscids</TD>
<TD align=middle>Apr. 24</TD>
<TD align=middle>--</TD></TR>
<TR>
<TD align=middle>Epsilon Arietids</TD>
<TD align=middle>May 9</TD>
<TD align=middle>--</TD></TR>
<TR>
<TD align=middle>Arietids (May)</TD>
<TD align=middle>May 16</TD>
<TD align=middle>--</TD></TR>
<TR>
<TD align=middle>Omicron Cetids</TD>
<TD align=middle>May 20</TD>
<TD align=middle>15</TD></TR>
<TR>
<TD align=middle>Arietids</TD>
<TD align=middle>June 7</TD>
<TD align=middle>60</TD></TR>
<TR>
<TD align=middle>Sigma Perseids</TD>
<TD align=middle>Jun. 9</TD>
<TD align=middle>40</TD></TR>
<TR>
<TD align=middle>Beta Taurids</TD>
<TD align=middle>Jun. 28</TD>
<TD align=middle>25</TD></TR>
<TR>
<TD align=middle>Lambda Leonids</TD>
<TD align=middle>Aug. 25</TD>
<TD align=middle>5</TD></TR>
<TR>
<TD align=middle>Sextantids</TD>
<TD align=middle>Sep. 27</TD>
<TD align=middle>30</TD></TR></TBODY></TABLE></CENTER>
<P><B>H. REPORTING OBSERVATIONS</B><BR>As mentioned above, the NAMN is not
equipped to handle radio observations. Instead, we recommend sending your data
to:<BR>
<P>Christian Steyaert<BR>e-mail: 72650.3513@compuserve...
<P>It is recommended that observers contact him first so that he can specify the
format data should be submitted in. Also, he will need to gather the required
information about your location, radio set up, etc.
<P>
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