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Location: Blogs The Classroom SessionsFM Radio Astronomy |
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| Posted by: Matthew Fox |
11/4/2007 |
This is the first of a series of documents that explain the wonderful hobby of FM Radio Meteor Astronomy. This set of documents fully explains in a non-technical fashion, the theory and implementation of your own FM Radio Astronomy Lab
Do you enjoy watching the night sky? Have you ever been known to gander towards the heavens, watching the stars slowly pass above you? Do you occasionally study the moon, it's phases, and where it is in the sky? Do you occasionally set aside some time to plan ahead for meeting up with friends to watch the next major meteor shower? And have you ever set your eyes in one part of the sky, just to see if one of the 'stars' is quickly moving directly overhead? If you have said "Yes!", to any of those questions, then I would like to say hello to you, as an astronomer friend. I have always had an obsession with the night sky. My Dad first explained to me when I was 8 years old, that the star I was seeing moving quickly overhead, wasn't really a star at all; but a man made satellite! "Wow!", I remember saying to myself. It just wasn't comprehendable to me. I relate my feelings then as to what my Grandfathers Mom must have thought many years back. My Grandfather Robert told me that when he was just a kid, he was outside the back porch one summer night watching the stars. His mom was inside doing the dinner dishes, when Robert started yelling excitedly for his mom to come outside. In a panic, she raced out the back porch and asked Robert what all the commotion was about? "Mom, look there...", he yelled pointing in the direction of a moving star. "That's a satellite! We put that into space, and it's over 200 miles above us, moving at over 15,000 miles per hour!!! We can see it because the satellite is reflecting the sun's rays!" His mom studied the moving star for a moment, and then looked at Robert, paused, and then took the dish rag and hit it over his head exclaiming, "Robert... you need to quit dreaming up these wild things, get back inside and do your homework!". Little did my Grandfathers mom know, but he had just studied about satellites in school a few weeks before!
Just as the our Ocean has so much left unknown, so does our outer space; if not more! When viewing pictures that the Hubble has recently taken, I forget that just a square centimeter of that picture of a Magellanic Cloud is really light years across! I forget that when I'm looking up at the stars at night, that I'm really seeing the stars as they were hundreds and thousands if not millions of years ago! Our view of the night sky is truly the only time-machine that we have here on earth! There is so much out there that we can't and don't know. It's an awesome balance of nature and our planet Earth is only a miniscule spec of space dust caught up in the balance of the gargantuan heavenly orbit.
Because I'm a simple man, and the thought of trying to understand all of the unknown is more than I can handle, I prefer the simpler side of astronomy. My personal astronomy tools include a 4.5" reflector telescope, a pair of binoculars, and a FM Radio! So your asking, "FM Radio?". Well... I love to tune into the oldies and listen to some Hendrix or Three Dog Night while viewing the heavens! Ha ha! No - not really. I actually love listening to static, and the occasional ping produced from 'stray' amplified radio waves. Okay... Okay... don't click on your browsers Home button or Back button just yet. Give me a chance to explain! This is something that thousands of amateurs and professional astronomers alike have started doing recently.
Observation of the heavens is harder or more difficult than most people think. A lot of things need to be just perfect to make the most of a night of visual observation.
- a clear clean sky subject to the least amount of *light pollution possible
- the weather must be cooperating - forget about visual observation when it's raining
- a full moon can increase light pollution too - unless you are observing the moon!
- generally speaking, you need "a night sky" (it's hard to visually observe during the daylight hours)
Most of all, you need patience and time. Many of the things above are beyond our control. We can't control when it's day or night and we can't control the weather. That doesn't leave us much time. Then we are at the mercy of our daily schedules to determine when we have time to relax and observe. But this isn't necessarily true of FM Radio Astronomy.
Being an astronomer isn't just about observing the heavens by using a telescope. Amateurs and professionals alike enjoy many different methods of observing the skies. As I stated earlier, FM Radio astronomy has been gaining popularity lately due to its ease and uniqueness. It's unique, due to the fact that it's not a visual observation technique, but an audible observation. For the techno-geek, it's called listening to Forward Scatter. The technique that I explain isn't for listening to the heavens, the moon, or the pulse of 'nearby' binary star. It's a technique for listening to falling meteors. That's right! You can 'listen' to falling meteors! "Why would I want to listen to meteors?", you ask? Well, mainly because it's "*geekish" and it can be done day or night, rain or shine. Well, actually let me correct my self. You could probably listen for falling meteors during a small steady rain-shower, but it would be hard during a thunder-shower. Lightning would cause interference that would make it difficult to distinguish meteors from lightning. Andy passing-by airplanes can cause interference as well, but these are just a few of things that make this hobby so exciting. Lighting, airplanes and meteors all have their own specific audible signature mark. So for a seasoned FM Radio Astronomer, it's fairly easy to distinguish between 'interference' and an actual falling meteor.
And you don't have to necessarily listen to falling meteors. NASA recently called upon amateur and professional FM Radio Astronomers alike to volunteer. They wanted signature data from different FM Radio Astronomers to record the re-entry of a de-orbiting satellite. They used this data from different observers to triangulate and document the re-entry process. Other amateur observers have web-sites that you can join, and submit your findings of fallen meteors in order to give more accurate predictions in the future for meteor per/hour peaks. They make available free software that you can use with your computer to ease the process; and make it more 'geekish' as I like!
Theory Time
Okay, I wouldn't be doing you a service if I didn't include a little theory. Don't fret! I won't get technical. But a basic understanding of the theory behind FM Radio Astronomy will go a long way in you being able to successfully implement your own FM Radio Astronomy lab and listening to the meteors.
Forward Scatter: This is what you are really 'listening' for. Forward Scatter is the result of the reflection of a radio signal off the ionization train of a meteor from a transmitter to a separate receiving station. Let's simplify this further.
The ionization train, for all intents and purposes, is the visible fireball trail you see when a meteor is falling through the atmosphere. The transmitter is a FM Radio Station tower that you have tuned your receiving station (or FM Tuner) into. Just as you tune your car radio into "KQRC 98.9 The Rock" to listen to the latest and greatest rock-and-roll, you need to tune into an appropriate radio station to listen to falling meteors.
So now you ask, "How do I know what station to tune my FM Radio into to listen to falling meteors? My city doesn't have a listed FM Meteor Station!". You are right. I'm not aware of any city that lists the local FM Transmitters to tune into for falling meteors. This is probably the hardest part of this hobby; trying to find a suitable station to tune into. But don't worry to much. I'll explain ways to find the appropriate stations.
When a meteor falls through the sky, in essence it "burns up" due to the friction from falling through the atmosphere at such a high rate of speed (ionization train). This burning up has an electrical effect on radio waves passing through the air. This effect is called amplification. Always remember that amplification is our friend! So we must now know how to harness this amplification effect and use it towards our intended goal; that is, to be able to listen to it. The amplification is very minuscule, and requires that you tune into a very weak radio station in order to hear a meteor ping. Meteor ping is what we amateur's call the sound made from the FM Tuner when we successfully hear a falling meteor. It really does sounds like a 'Ping'. So you just can't tune into any FM Radio station that you like. Local radio stations wouldn't work because they would way overpower the amplification the meteor creates when falling through the atmosphere. The idea here is to tune into a high-powered radio station that is too far away for you to actually listen to. In essence, all you will hear is static when you are tuned into the correct station. By tuning into a station that is far away, you will be able to detect the Meteor Ping amplification. You will perceive this amplification as a "Ping" sound on your tuner.
So here is the step-by-step lowdown.
You tune into a high-powered radio station that is out of your listening area. You will be listening to constant static on the receiver. As a meteor falls through the atmosphere, it will amplify the stations radio signal that you are tuned into. You will percieve this amplification as a 'Ping' on your receiver. Viola! There you have it.
Refer to the diagram below for a pictorial description. The circular dark-blue area on the map represents your local listening area. That's your house in the picture with all the antennas sticking out everywhere! All radio stations within this area would be too over-powered due to your close proximity of these stations. The light-blue colored area are the radio stations outside your listening area. These are the stations that would provide the best listening experience. As the meteor falls between you and your tuned in FM Transmitter, the falling meteor amplifies this signal slightly, and your receiver picks this up as a "Ping" through your speaker!
So what do I need to get started?
At the very least, all you need is a FM Radio. But without upgrading your lab, you will find it harder to listen to falling meteors. You may want a few more things. This document is geared towards a nice little FM Radio lab. You will find that most of the items are very inexpensive. And as always, feel free to experiment! The possibilities are endless.
- FM Radio Tuner : I suggest that you get a digital tuner. It's much easier to determine what station you are tuning into because almost all digital tuners have a LCD Display that shows you what frequency you are monitoring. FM Tuners can be bought at your local electronics store. Take a quick search on eBay and you find them dirt cheap! I bought mine on eBay for $10.00 with free shipping.
- Yagi Directional Antenna: Again, you can find these at your local Radio Shack, and they are even cheaper on eBay if you have the time to spend looking. It's important that your antenna is directional. That is, pointing it in the direction of your FM Transmitter limits the amount of interference you would get from a non-directional antenna.
That's all you need for a basic lab. But if you want to get a little more "geekish", add the following items to your lab.
- A computer running Windows 2000, XP or higher. You need a sound card in order to record your meteors.
- Software to record your findings. There is free-ware out there that you will find very useful.
The extended lab, or "geekish" lab as I like to call it, will allow you to constantly monitor for falling meteors, without you having to be physically present to constantly monitor the radio. The free software that is available can automate the process for you, and find the Meteor Pings automatically. That way you don't have to monitor through hours worth of static just to find your meteors.
Please refer to the next document of my series titled, "Building your own FM Radio Astronomy Lab" to learn in more detail how to make your FM Radio Astronomy Lab a reality!
Glossary
| Geekish: |
That which involves being a 'geek'.
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| Meteor Ping: |
The sound you hear from your FM Receiver when a Meteor passes through the radio space between you and your FM Transmitter radio station that you are monitoring. The radio transmission is temporarily amplified by the meteor passing through the atmosphere and it's this amplification that makes the distinct 'Pinging' sound on your FM Receiver.
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| City Zip Code Center: |
This is the generalized center of your city based on your Zip Code. Data was provided by the U.S. Census Bureau.
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Radius:
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The length of a line segment between the center and circumference (perimeter) of a circle.
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Comments (3)
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Re: Part 1 - FM Radio Meteor Observations - What's this all about? |
By karen on
1/21/2008 |
| Hi,thanks for this info - ive been searching round for something that makes this accessable and your website has done just that - i am in australia - i was thinking about joining up tot eh radio jove but i like the nmeteor idea much better.. cheers Karen |
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Great site |
By Simon on
6/17/2008 |
| Hi - your website is very helpful and interesting, thanks for making it! |
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Re: Part 1 - FM Radio Meteor Observations - What's this all about? |
By Alex Rivera on
8/11/2008 |
| I`m working with radio FM meteor detection during few months. I hope success with your tools. Thanks in advance. |
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