(meteorobs)

[GeoZay at aol.com]

>>Hi
How do you spot  meteors using a radio ?
What frequency do you use?
How do you know when  you have heard one?
All I hear is the normal of frequency   static
Regards Ian<<
 
Hello Ian...here's a little ditty  I wrote a long time ago...hope this gets 
you in the ball  park.
George Zay

---------------------------------------------------- 
CHAPTER VI   FM RADIO MONITORING OF METEORS 
George Zay 
6.1  Introduction 
Monitoring meteor activity by radio got it’s start right  after World War II. 
It was then found that meteors could reflect radio signals.  There are two 
ways that radio meteors can be detected. One is known as  backscatter. 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. 
It has been learned that when a meteoroid enters the  atmosphere, the plasma 
in the meteor’s wake and coma reflect radio waves. The  resultant ionized 
column of gas molecules and free electrons has the ability to  reflect radio 
signals from a transmitter to a distant receiver. The frequency  range that this 
occurs is between 40 and 150 MHz. Although the optimum lies  between 40 and 70 
MHz, the common FM band is frequently used for forward scatter  work. This FM 
band is between 88 and 108 MHz. 
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. Transmission from the station is not  heard, 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  up to 
minutes in duration. This contact manifests as a signal increase in a  piece of 
music, voice or noise. Since this technique uses electromagnetic waves,  it can be 
used during daytime when there is a bright moon, or during cloudy and  rainy 
weather. 
Radio signals reflected off a meteor’s ionized and free  electron column is 
done in two ways. These are known as Underdense and Overdense  echoes. 
Underdense - Underdense  echoes are caused by a weakly ionizing meteor. Which 
means only a few electrons  will be reflecting the radio waves. With this 
configuration of ionization, the  radio beam will be reflected pretty much like 
that of light with a flat mirror.  The ionized column has to be aligned 
correctly to reflect a signal from a  transmitter to a distant receiver.  
Overdense -  Overdense echoes are caused by a  strongly ionizing meteor. 
Which means that a high density of electrons are found  in the meteor trail. This 
high electron density has the looks and behavior of a  cylinder that reflects 
radio waves in all directions. Radio reflections can be  detected even when 
the ionized column is not aligned like a mirror to reflect a  signal. This 
allows the detection of overdense meteors in a larger area. Also  the number of 
overdense echoes will increase much steeper during a major shower  maximum than 
the underdense echo number. This is not only due to the lower  population 
index, but mainly due to the easier alignment for  “bright” echoes to be detected. 
 
This ability of meteors to reflect radio signals to  distant receiving 
stations has found a practical use within the weather service.  In remote locations, 
automated weather equipment transmit their accumulated data  to distant 
weather stations by relaying their signals off the ionized meteor  trails. The 
automated transmitter “senses” the presence of a meteor having the  proper 
alignment and transmits the accumulated data in a very short  period. 
6.2  Equipment 
Get an FM radio, but make sure it is of the digital kind  and that it has a 
shielded cable connection where the antenna plugs in. Digital  ensures that you 
are on the desired frequency without any  guessing. 
You next need an FM Yagi styled radio antenna. You can  get one at Radio 
Shack for about $17 or pay more (about $150) for a more  directional one from a 
local TV antenna company. Unfortunately which one to get,  depends on trial and 
error with the cheaper one first. Assuming that you got the  Radio Shack 
brand, hook your antenna to the radio with co-ax  cable. 
6.3  Finding Your Monitoring  Frequency 
Now punch in the frequency's one at a time from 88.0 to  108.0 MHz. What you 
want to do is write down all the frequencies that you do not  hear any kind of 
music or talking. All you want to hear is static noise. Be sure  to turn the 
antenna all the way around (360 degrees) to find this static area.  You do not 
want the antenna very high, because in most places in the US you  might 
receive unwanted continuous reception. So 6 feet is about it. The lower  the 
better, but beware of the tripping factor. Find a safe spot. Somebody is  bound to 
trip on it and most likely it will be yourself.   
If you are lucky, you will find several or more  frequencies where nothing 
but static is heard. These are your potential useable  frequencies. If you do 
not find any, you have two  options: 
i) Move your radio equipment  to another location, preferably in a valley and 
many miles away from the city  (30 plus miles). or... 
ii) Buy the more expensive and  directional (and most likely larger 12 foot 
long antenna), and try all the  frequencies again. If that does not work, try 
another location. If that do not  work, consider a different frequency band 
before  punting. 
Assuming you got a few useable frequencies. Most likely,  somebody is 
transmitting on these frequencies at least 200 to 1000 miles away.  You do not know 
from which direction though. So you must go to your local  library and find a 
book that lists the frequency and station locations. It’ll be  in the Reference 
Section. I found you are better off just going to the  Information area with 
your “hat-in-hand” and ask for help. Once you get the  book, just look up the 
stations that are transmitting on the frequency you only  hear static. If the 
library does not have such a book, look in phone books of  different major 
cities located within 200 to 1000 miles in the Yellow Pages  under “Radio 
Stations”. They usually list the frequencies along with addresses,  etc. Knowing 
their output is not really that important. Just try to find one  that mentions 24 
hour transmission and seems like a major commercial  broadcasting station. If 
they have that, they are transmitting with a reasonable  amount of power. 
Ideally choose a station that transmits over 30 kilowatts and  is located about 
300 to 500 miles away. List them all, just in case they are  needed later. 
6.4  Setting Up 
Okay, you have done all the initial leg work. Now find  your location on a 
decent map. Find the transmitting station’s location also on  the map. With 
Geographical North being 0 degrees, find what degree angle the  transmitting 
station is to you. This is the Transmitting station’s  Azimuth. 
Next step, take a compass to find True North with your  antenna pole at the 
middle. Be sure to do this with the pole and other metal out  of the way or you 
will get a false reading. Turn the antenna to point towards  your 
transmitting station. Use a protractor. I personally cemented a short piece  of antenna 
pole into a 5 gallon bucket. This way I can move the bucket around,  but it is 
heavy. If you do this, cement the short piece at a 45 degree angle or  as 
close as you can. When you slip in the other short piece with your antenna  
connected, this will give you the 45 degree angle without fooling around too  much. 
If instability is a problem, place a heavy rock on top of the bucket. If  you 
have not done the above, tilt your antenna so that it points up at a 45  
degree angle instead of the traditional horizontal  flat. 
6.5  Operations 
Now just listen. All you hear is static. When my daughter  was young, she 
called this “Fuzz." When a meteor comes by, it may or may not  (depending on 
angles and all kinds of things), produce a signal. You will hear  more signals 
than you see. Your radio can detect meteoroids down to 8th  magnitude at least. 
Most are very short signals on the order of 1/4 second. They  are actually 
small segments of what is being transmitted. They sound like bumps,  thumps and 
chirps. The longer signals are actually recognizable pieces of music  or 
talking. These are usually very sudden, loud and clear. They begin suddenly  and 
often end abruptly. From my experience, in-sight aircraft will interfere  when 
they fly by. They usually sound gradual before getting real loud. I  distinguish 
aircraft reflections from long duration meteor signals this way:  Aircraft 
makes increasingly loud, but very scratchy signals with interfering  multiple 
radio stations. Meteors are loud, but very clear on one radio station  only. 
During your observations, I highly advise you to use one  frequency 
exclusively with your antenna pointed in the same direction with the  same elevation 
always. This way, your day to day monitoring establishes a  reliable pattern 
that can be compared without being a variable. On the average,  you will hear the 
least amount of meteor activity around 6 p.m. and the most  around 6 am. A 
typical hourly rate for me around 6 p.m. is 7 and around 6 am is  about 40. 
Rates will vary, but should be somewhat proportional to this. Of  course, a major 
shower could change all this. 
6.6  Recording 
Now to record your data. I made my own recording form. I  was driving myself 
nuts in noting the times and signal duration for every little  meteor bump. I 
bought myself a small hand counter and simply pressed the button  for every 
signal heard, regardless how long the duration. If the signal was 1  second or 
longer, I would note them separately in an appropriate box. I do this  at half 
hour increments for each hour, although only 1 hour periods of data are  
considered useful. 
You can interpret signals lasting more than 5 seconds in  duration as being 
most likely caused by a visually bright meteor. The pattern  does seem to hold 
that there will be more long signals produced by brighter  meteors (-1 
magnitude on up) than less bright meteors producing long radio  signals. Also, it’s 
been noted from some observers that signal duration’s tend  to differ from 
frequency band to frequency band. Signal duration’s tend to be  not as long at the 
FM band level as it is with frequencies near 50  MHz. 
I often observe visually with a speaker next to me and do  my radio observing 
work simultaneously. Sometimes I get simultaneous events to  which I note on 
my recording form. I have noticed that if I monitored the radio  at night 
only, my brain dissipates and I am destined to fall asleep at the helm  in short 
order, or at least miss a healthy percentage of the reflections. When  this 
happens, I must discard the doubtful portions of  data. 
6.7  When to  Listen 
Actually, you can listen for meteors anytime of the day  or night. Generally, 
the most active 12 hour period is from Midnight to Noon.  Major shower 
activity usually produces exceptionally high hourly rates both  audibly and 
visually. So much so, that the radio can quickly become saturated  with reflections 
that it produces continuous radio reception. At this point,  it’s almost useless 
to maintain hourly rates. These moments are exceptions to  the rule. 
Just about everyone knows about the night time meteor  showers, but not 
everyone knows about the daytime showers. These are almost  exclusively monitored 
by radio. Usually these occur shortly after sunrise. For  your convenience, IMO’
s list of daytime showers is listed  below: 
Cap/Sagittarids                                Peak on Feb.             1     
                ZHR 15 
Chi-Capricornids                             Peak on Feb.             13      
             ZHR 5 
Piscids (APR)                                   Peak on Apr.              2 
Delta Piscids                                   Peak on Apr             24 
Epsilon - Arietids                        Peak on May             9 
Arietids (May)                                Peak on May             16 
Omicron - Cetids                          Peak on May             20          
         ZHR 15 
Arietids                                          Peak on June             7  
                   ZHR 60 
Zeta Perseids                                  Peak on June             9     
                ZHR 40 
Beta Taurids                                  Peak on June             28     
              ZHR 25 
Gamma Leonids                        Peak on Aug             25 
Sextantids                                      Peak on Sept             27   
     ZHR  30 

6.8  Where to  Send Data 
Okay, so you have started your monitoring and you have  piles of data stored 
up. This information is totally useless if you keep it in  some file where it 
will never be seen again. I recommend sending your data to  Christian Steyaert 
in Belgium. His mailing address is:          
Christian Steyaert 
Kruisven 66  
B-2400 Mol 
Belgium 
e-mail:  Steyaert at ws.innet.be 
I recommend contacting him first so that he can give you  the format for your 
data. Also to get other pertinent info about your location  and radio set-up, 
etc. 
I am primarily an observer that started listening to the  radio as an aid to 
keep me alert during my long observing sessions. Radio  monitoring meteors is 
a lot more complicated than what I presented. If you first  grasp what I have 
written here, you will be ready to dig a little deeper into  this field.