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jarbi

My meteor detection system

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Hi Everyone,

Recently I started up with meteor detection here in Belgium, joining a group of 15 enthusiast people. I just would like to share with you how did I start up and how it looks like.

1. We have an 5W transmitter on 49.99 MHz in Ieper ( Belgium ), this is on continuously and transmits in all directions.

2. You need a simple Yagi antenna for this wavelength ( 6m ), mine is a CUSHCRAFT A503S with 3 elements. You can also make one, see design attached.

Point the antenna in the direction of Ieper. The elevation should be : arc tan ( 90/ dist *2 ), where dist is your distance to Ieper.

3. The radio receiver is the crucial part. It should be able to tune to 49.99 MHz ( most easy way if it has digital display ), with USB mode.

4. Connect the audio output of your receiver to the line in of your PC. Install the free software SPeclab on it, it is a spectrum analyzer.

5. Start speclab, and set it up to record jpg-s and wave-s of the detected Doppler event from meteors ( it is a longer story, I needed two days to learn how to set it up correctly ).

AND THIS IS ALL POSSIBLE FROM THE UK ALSO, because we know someone who is doing it from London, using the transmitter in Ieper.

So, it's time to show something how does it work in practice. I will gather some pictures/screenshots and will come back soon..

cheers,

Janos

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So, some pictures as promised.

1. The antenna ( temporary setup )

Stargazers Lounge - jarbi's Album: Radio astronomy - Picture

2. Pictures from yesterday's meteors. These are automatic screen captures, taken by Speclab. You can see some slow Doppler-efffects also ( reflections on airplanes ). The vertical one's are meteors !

Stargazers Lounge - jarbi's Album: Radio astronomy - Picture

One addition to my previous post: the link for Speclab is here:

http://freenet-homepage.de/dl4yhf/spectra1.html

Some more explanation to the pictures. What you see is time on the horizontal axis and frequence on the vertical axis. Speclab is creating a shifting "waterfall" of detected sound intensities for every frequency in the displayed range. This is moving to the left, so you get a history of frequency changes. I record the sound also ( 5 KHz is enough ), so you can acually hear a short beep when a meteor is coming. This is resulting in one JPG and one WAV file in every 5 minutes, which I evaluate every day. This way we can make a very accurate statistics about the number of meteors. Having more simutanious observations can be used for calculation of the direction/speed of the meteor as well. Since I am just starting, I cannot tell much more about it so far.

cheers,

Janos

Stargazers Lounge - jarbi's Album: Radio astronomy - Picture

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nice one - i was looking @ this the other day - but its a little new to me - so confusing

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Quite the interesting setup. Certainly something I think I will get into when funds become available.

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Thanks for the link as well. I didnt know they had freeware analyzers!

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Thanks for your replies,

One update from today: I have placed the antenna on a proper mast, see photo below.

Talking about budget, the whole setup was just above 300 EUR, most of it was the radio receiver ( second hand ), antenna and good antenna cable. If you decide to build a Yagi yourself, you certainly spare 100 or more. I was too impatient to do so..:).

Please reply or PM me if you are interested in more details.

cheers,

Janos

post-13278-133877385453_thumb.jpg

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Hi Janos,

You make it sound so easy! :)

I had a go at this last year and it was extremely frustrating. In retrospect, I had completely the wrong equipment - my receiver didn't operate in the correct frequency range, couldn't receive USB signals, and I was using a multi-element UHF TV antenna. I spent several fun evening listening intently to static... :)

I'm really impressed with your results. Particularly amazing that you're just using a 5W transmitter - I was expecting to have to listen for 100kW TV transmissions!

Baskii

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Hi Janos,

You make it sound so easy! :)

I had a go at this last year and it was extremely frustrating. In retrospect, I had completely the wrong equipment - my receiver didn't operate in the correct frequency range, couldn't receive USB signals, and I was using a multi-element UHF TV antenna. I spent several fun evening listening intently to static... :)

I'm really impressed with your results. Particularly amazing that you're just using a 5W transmitter - I was expecting to have to listen for 100kW TV transmissions!

Baskii

Baskii,

It doesn't only sound easy - it IS easy when you join a group of dozen amateurs. I received all practical/technical info I needed, and I was in business in 3 days time :headbang:. It is of course not that easy when you try to start on your own...

I think the secret is that 49.99 MHz is not used by any radio stations. That way you have a minimal amount of background noise, including "radio pollution" from electronic equipment in your neihbourhood ( badly shielded motors, drilling machines etc ). The other reason why 5W transmitter is enough that tha USB bandwidth is quiet narrow. I didn't explain in details, but the transmitter sends a modulated sound signal on the Upper Side Band ( USB ) of the 49.99 MHz carrier, so you know exactly what to look for, the reflection of the meteor is not spread through a wide fequency range.

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Hi,

Just to show how fascinating this can be, please check out this JPG below. It shows a special "epsilon reflection" on the left, this is caused by an expanding ionised reflective cone ( created by the meteor ).

You can see reflections from both sides of the cone ( one side is approaching the other is going away ), that is why you see ( and hear in the wave-file ) a double Doppler-effect in opposite directions. To see this effect the meteor has to come from the "side", so more or less perpendicular to the line between the transmitter and receiver.

There are also two "regular" meteor reflections shown shortly after the 01:27 & 01:29 mark.

cheers,

Janos

post-13278-133877385699_thumb.jpg

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Fascinating... can you upload one of the sound files Janos?

Arthur

Athur,

Here you go:

RapidShare: 1-CLICK Web hosting - Easy Filehosting

As you see the file name of the WAV file shows 01:25 and not 01:30 like the JPEG image. The reason: a wave file is created at the beginning of every 5 minutes but the image is only saved when the "waterfall" display is ready at the end of a 5 minute period.

Sound quality is not superb ( 5 kHz ), but with reason: I run this system continuously, so high quality=large sound files - the disc is more quickly full. The first meteor-sound is like two detuned flutes, but when you hear the second meteor you will say it's a more than obvious Doppler-effect.

cheers,

Janos

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Hmm, the flutey bit at the start was sort of understandable, if a bit longer than I expected but the later one really only sounded like a spring boucing to me?

Arthur

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Hmm, the flutey bit at the start was sort of understandable, if a bit longer than I expected but the later one really only sounded like a spring boucing to me?

Arthur

Arthur,

As you probablty know the speed of the frequency change in a Doppler effect is more steep when the radial speed of the object is bigger and vice versa.

The first sound shows a very seldom slow doppler effect, because the expansion speed of the ionized cone of air is very slow comparing to the speed of the meteor.

In case of the second meteor, you hear a flute tone wth quickly decrasing frequency - it means the meteor was moving very quickly when entered the atmosphere. From the length of the sound effect and the amount of frequency change it is possible to calculate the radial speed of the meteor ( I can lookup the exact maths if you are interested ).

cheers,

Janos

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Hello Janos,

As a collector of meteorites I find your post very interesting, even though the science behind it is beyond me. I can see that there are practical applications in regard to meteor counts, but can you use this system to distinquish a potential fall and to predict its location?

Regards, Kieron

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Hello Janos,

As a collector of meteorites I find your post very interesting, even though the science behind it is beyond me. I can see that there are practical applications in regard to meteor counts, but can you use this system to distinquish a potential fall and to predict its location?

Regards, Kieron

Hello Kieron,

I think we can detect a potential fall, because than you have a huge reflection which lasts for some minutes. But we can only detect something when it enters the atmosphere between the observer and the transmitter.

Regarding location of fall, it is possible to calculate the direction and angle of the meteor ( when more observers detect it from different locations ), but we never know distances. And without this there is no chance to trace location I am afraid...

cheers,

Janos

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Thanks for your reply, Janos - a most interesting topic.

Best wishes, Kieron

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Just to append some results of the last two days - sound spectrum analysis of 3 reflections. On all three you can see a relatively steep descending fequency line at the beginning - it shows that the meteor is slowing down very quickly. Than the speed stabilizes when the atmosphere has slowed it down, the line ends when the meteor has burned. On the third image you can also see some "sparkling", it is caused by quick intensity/reflection changes in the burning process.

cheers,

Janos

post-13278-133877385958_thumb.jpg

post-13278-133877385962_thumb.jpg

post-13278-133877385967_thumb.jpg

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Hi Jarbi,

Just wondering if you were making any radio observations during last night's Perseid peak? Since it was cloudy you probably got more out of it than I did..!

Baskii

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Hi Jarbi, This setup looks very interesting, myself and a friend are very keen to give it a try, we've got the radio side of things pretty much sorted, all the parts for the antennae are ready to start piecing together and the radio seems to be working fine.

Could you possibly give a bit more detail on the configuration of the SPeclab software, i've been playing with it for a while now and am still no closer to working it out.

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Hi Ryan,

I am on holiday abroad until monday, so I don't have access to my system at the moment. I will come back to you as soon as I am back home. I will send my ini-files from Speclab, and some guidelines to setup the frequency waterfall and wave/jpg recording.

You may start already by directing the antenna correctly. If you are intending to try our beacon, it is at 2° 55 E ,50°49 N ( Ieper, Belgium ). Please calculate the elevation angle of the antenna to point at 90km above the surface at the half distance between you and the transmitter. The exact frequency is 49.99 MHz, your receiver needs to be in USB mode. In this mode you should hear meteor reflections as about 800 Hz audio beeps ( depends a bit on actual wind speed and other parameters). Good luck !

cheers,

Janos

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Hi Ryan,

I have checked now what do you need to customize in Speclab. I would like to send you the ini-files, please PM me an email address where I can send them. You will need to replace the original ones with these.

Additionally, you need to adjust settings for scheduled actions to reflect your Pc and location data. This is under File/Screen capture/Screen capture options. You need to adjust the first and third tab ( after replacing the original ini-files ).

Please reply how is it going, I am very curious !

cheers,

Janos

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Hi Jarbi,

Just wondering if you were making any radio observations during last night's Perseid peak? Since it was cloudy you probably got more out of it than I did..!

Baskii

Hi Baskii,

During the maximum I was on holiday, but now I start analyzing the recorded data. This week I am preparing all my gear for the yearly belgian star party this weekend, so it might get a bit delayed :).

cheers,

Janos

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Hi Janos

just came across this thread ...

Are you sure about what you say on the doppler shift being caused by the speed of the meteor ? The signal comes from the ionisation trail, which will be stationary (although blown by winds). I understand there large meteor can cause a sort of shockwave which will give a doppler shift, but generally I can't see that you would get a speed related doppler. Help.

bests

Justyn

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Is this transmitter still switched on and working?

Thanks,

Paul..

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