Proper freq/observing technique for detecting meteor scatter by FM radio?

[banah]

Hello, masters!

I am absolutely a newbie, lives in Sweden, and just interested to detect meteor scatter by radio with VHF. 

Although it seems most people uses HAM radio, I am using normal FM radio from rubbish bin. (available FM freq range 87-107Mhz) I built my 3 element Yagi originally designed for targeting 91Mhz(+4dB) but it seems work with other freq band

as well. I had caught only few local station without Yagi, but now I can receive around 30 stations. It is installed at my balcony 14m height from the ground.

I was so exited to detect meteor but I have no idea where I am going to now. Even I've read many articles but still there are so many things I can't understand.

So could you masters please give me some advices? It would be really appreciated if you give anything advisable to me.

1. Which freq I have to use? 

 As I wrote, the antenna was designed for 91Mhz, which was picked up depend on FM transmitter reference and my antenna direction(SE).

 Highest power / 600~800Km distance from receiver / avoided from local stations

 But unfortunately I couldn't have listen any of interesting things from targeted freq. Instead of that, I found some other bands (for instance 102.4, this is also transmitted from Poland Warszawa) which I can hear strange ping. 

 So I wonder what's wrong with my circuit, is it okay just using other bands with the antenna which was designed for other range? It might be happened because my antenna building wasn't perfect?

2. Even though it's okay use the other band, my spectrum of sound seems not that much like real meteor's which I've seen from other explorers...also I guess this is too(?) frequently appearing now.

 I've seen many categorized meteor shape on the spectrum, but mine doesn't looks like that at all, sounds as well.. (It's okay, I didn't expect I could listen meteor every minutes. but then where they comes from???) 

here, some of things I've got..(basically they were white noise as input, I got them through band-pass filters / denoise threshold level.

 case 1)  consistent ping, and something broad in lower freq.

               I have no idea what are they. I was quiet happy when they appeared as if I found something. But I became do not trust they are meteor. 

 case 2) still some broad things appear but hardly possible to listen.

             Also, some pings which are sound like Morse code, usually horizontal figure. But they are not always on the same freq. Sometimes makes curve as well. Does it makes any difference?? 

Honestly I have no idea if I did properly set up system / my Spectrum lab. Because most articles were written for 54/143Mhz with proper receiver, I couldn't adapt them to my cases as it is.

My system quiet primitive that ( Ant - FM radio - Laptop / used 75 impedence coax / common audio cable ) I guess the FFT/audio card set is most critical, attached my things below. (audio card sample rate = 32000 )

3. I have more fundamental question, everywhere I've find radio meteor scatter sounds such as echo, ping..

But why they should be like dolphin sound? I mean if they are really reflected radio wave from radio station somewhere, then shouldn't I listen possibly human voice from radio station??

Thank you for reading my questions. I hope to be enlightened soon.

[The Admiral]

Hi Banah, welcome to the forum, and to your new pursuit. I don't know that I can answer your questions as I've no experience of using FM broadcast stations for meteor detection, and I'm not sure that I'd be able to analyse your screen saves, though traces 2, 3, and 4 do show what look like meteor returns. However, I have a few thoughts.

As you probably know, meteor detection is best done with a continuous radio wave, preferably unmodulated. That is not to say that you'd not be able to get some results using FM transmitter signals, but the spectrum of the FM signal is complex so I'm not sure what a meteor reflected signal will be like. I would imagine, though, that you would get transient snatches of the broadcast programme. After all, communications by meteor reflection is something that some amateur radio enthusiasts pursue. Another thing is that, normally, one would choose a transmitting station "over the horizon" so that, ordinarily, you wouldn't be able to detect it. It is only when it is reflected by the meteor that it becomes detectable. If you didn't do that,  your faint meteor signal will be lost in the "direct" signal, though of course that would depend on the signal strength of the direct signal. In turn, that will require you to "tune" to the distant station without actually receiving it, which in turn requires you to have a receiver that will enable you to do that precisely. I've also read that you will need to find a distant transmitting station that transmits on a frequency where your reception is not swamped by your more local stations, and that may be a problem as the FM band is quite congested. This is not helped by the fact that the FM broadcast signal is typically 100kHz wide, thus enhancing potential overlap. This will probably dictate which frequency to use at your location. If it was me, I'd probably tune around to find the "quiet" frequencies and use published information to see if there were distant stations transmitting on those frequencies that I could target.

I wouldn't have thought that the SL settings would need to be different for use on other frequencies. I wouldn't have thought either  that the use of a Yagi, designed for 91MHz, on other frequencies would give rise to problems; it might not be as sensitive as one designed for the correct frequency, and its polar response might go a bit awry, but it should work. Some designs are more broad band than others I believe.

I'm sorry I can't help further, but may be there is someone who has experience of this. I'm sure a web search for meteor detection using FM signals, which I guess you've already done, is likely to yield the most amount of information.

Ian

[John101]

Banah,

This download from Spaceweather dot com  >>“Pierre Terrier’s Meteor 4 software<< may help confirm your snippets of meteor scatter.  

http://spaceweather.com/glossary/forwardscatter.html

Congratulations too on ‘spectrumlab’ up and running, from my experience that was not an easy task.  

The Yagi is not only highly directional but polarity sensitive too,  vertical polarized if elements align to earth’s zenith, horizontal if parallel to earth suffice.

On earth, FM broadcast radio emission is vertical polarized.

Over-the-horizon (that is NOT line of sight) FM station meteor scatter reflection will be neither vertical nor horizontal but close to ‘circular’ polarization. For best meteor reflection rotate the Yagi on its axes for best over the horizon reception.  At best you will observe about 3dB (that is double) the advantage as you ‘twist’ or ‘rotate’ the Yagi on it ‘boom axis’.  

That said, note too, a change in Yagi azimuth and elevation make an extremely large difference (more than double) signal detection, therefore try 90  to 180-degree azimuth changes. Maybe this particular meteor shower is between you and the commercial FM station or flanked by the FM station.

Enjoy

John
N3AAZ
FM19xb
 

[banah]

Hello, Ian

Thank you so much for kind answer. It is super helpful to me. Now, at least I don't need to be obsessed about my antenna or SL settings. I am quiet relieved.

And "snatches of the broadcast programme" was exactly what I've imagined, although it never happened yet.

Yes, the FM frequency what I choose wasn't used by any radio station near my area, but transmitted from over the horizon. However you should be right. As most FM bands are overlapped, so there would be chaotic waves even though empty bands. In some cases, I could listen some vague radio programmes with heavy noises so I reckon they are reflected by meteor. However still there would be possibility that they were actually some fragment of local station. Unfortunately this is impossible to recognize the station precisely cause they are underneath the noises..

Sorry, I thought it could be so primitive question. But if I can ask you one more question, how could I find/determine "quiet" frequencies? It seems every frequencies are full of noise to me. I wonder if these noises are caused by congested FM band or my equipment? Or basically every frequencies would normally be with heavy white noises?

Hi Banah, welcome to the forum, and to your new pursuit. I don't know that I can answer your questions as I've no experience of using FM broadcast stations for meteor detection, and I'm not sure that I'd be able to analyse your screen saves, though traces 2, 3, and 4 do show what look like meteor returns. However, I have a few thoughts.

As you probably know, meteor detection is best done with a continuous radio wave, preferably unmodulated. That is not to say that you'd not be able to get some results using FM transmitter signals, but the spectrum of the FM signal is complex so I'm not sure what a meteor reflected signal will be like. I would imagine, though, that you would get transient snatches of the broadcast programme. After all, communications by meteor reflection is something that some amateur radio enthusiasts pursue. Another thing is that, normally, one would choose a transmitting station "over the horizon" so that, ordinarily, you wouldn't be able to detect it. It is only when it is reflected by the meteor that it becomes detectable. If you didn't do that,  your faint meteor signal will be lost in the "direct" signal, though of course that would depend on the signal strength of the direct signal. In turn, that will require you to "tune" to the distant station without actually receiving it, which in turn requires you to have a receiver that will enable you to do that precisely. I've also read that you will need to find a distant transmitting station that transmits on a frequency where your reception is not swamped by your more local stations, and that may be a problem as the FM band is quite congested. This is not helped by the fact that the FM broadcast signal is typically 100kHz wide, thus enhancing potential overlap. This will probably dictate which frequency to use at your location. If it was me, I'd probably tune around to find the "quiet" frequencies and use published information to see if there were distant stations transmitting on those frequencies that I could target.

I wouldn't have thought that the SL settings would need to be different for use on other frequencies. I wouldn't have thought either  that the use of a Yagi, designed for 91MHz, on other frequencies would give rise to problems; it might not be as sensitive as one designed for the correct frequency, and its polar response might go a bit awry, but it should work. Some designs are more broad band than others I believe.

I'm sorry I can't help further, but may be there is someone who has experience of this. I'm sure a web search for meteor detection using FM signals, which I guess you've already done, is likely to yield the most amount of information.

Ian

[banah]

Great! John, thank you tell me good point,

I haven't think about that. I've thought only transmitted polarization then just installed my antenna literally 'horizontal'. I'll try right now. But I am afraid how could I recognize if I got better gain? Because with my poor circuit, I could listen tuned radio station only. Please let me know if you have better suggestion, Thank you!

Banah,

This download from Spaceweather dot com  >>“Pierre Terrier’s Meteor 4 software<< may help confirm your snippets of meteor scatter.  

http://spaceweather.com/glossary/forwardscatter.html

Congratulations too on ‘spectrumlab’ up and running, from my experience that was not an easy task.  

The Yagi is not only highly directional but polarity sensitive too,  vertical polarized if elements align to earth’s zenith, horizontal if parallel to earth suffice.

On earth, FM broadcast radio emission is vertical polarized.

Over-the-horizon (that is NOT line of sight) FM station meteor scatter reflection will be neither vertical nor horizontal but close to ‘circular’ polarization. For best meteor reflection rotate the Yagi on its axes for best over the horizon reception.  At best you will observe about 3dB (that is double) the advantage as you ‘twist’ or ‘rotate’ the Yagi on it ‘boom axis’.  

That said, note too, a change in Yagi azimuth and elevation make an extremely large difference (more than double) signal detection, therefore try 90  to 180-degree azimuth changes. Maybe this particular meteor shower is between you and the commercial FM station or flanked by the FM station.

Enjoy

John
N3AAZ
FM19xb
 

[The Admiral]

I could listen some vague radio programmes with heavy noises so I reckon they are reflected by meteor.

 I'm not sure that these would necessarily be caused my meteors. Don't forget that meteor reflections last from only a fraction of a second to a few seconds, and that interference from various transmitters is quite prevalent and variable from moment to moment.

By "quiet frequencies" I mean those frequencies where there is no interfering signal. But you will always get background noise (just a hiss). So check out the band and see where all you get is hiss.

Ian

[The Admiral]

One other thing, banah, I wouldn't get too worried about the pointing accuracy of your antenna. 3-element Yagis aren't tremendously directional. Here's a plot for the 3-element Yagi published in Sky at Night magazine, at its intended 144MHz.

Note how broad an angle sensitivity is between maximum and 3dB down from max (magenta lines). So alignment isn't critical.

Interestingly, if this antenna is used for 100MHz, not only is there a tremendous impedance mis-match, but the sensitivity plot changes as well:

Of course, this is way off the design frequency. Using a Yagi designed for 91MHz at 102MHz isn't going to be as dramatic.

[banah]

Thank you Ian, I've just tried to change position of my antenna. What I've realized was it really influence the quality of band. It was really tough, groaning deal with 2m size antenna..

Even few changing few centimetre of antenna height and angle showed different gauge of signal level. (As I have no way to gauge dB level, I just saw the amplitude level on the radio panel.)

Some what I discovered now is those frequencies with consistent ping were actually local radio station programmes. I guess if the signal is too weak, then I might listen only ping. (After I changed my antenna position, I could listen local stations. What a disappointment!)

Now I have more detection of stations, so I've got more dense, crowded FM charts which I should avoid...

Anyway, I've enlightened how it is important to have proper position of antenna, but still I have no idea how I can test / determine the position for meteor...Might be possible to fine perfect angle for specific radio station, but signals from meteor usually not steady and just moment. Should I assume the wave reflected by meteor would have same angle? Any idea would be appreciated! 

[The Admiral]

It will have to be trial and error I think, though personally I don't think it is too critical (though some might argue otherwise). My antenna is horizontal and pointed just above the horizon in the general directionof the Graves transmitter. The recommendation, though, is to have the antenna in a vertical plane. One of the advantages of using 143MHz is that the antenna is smaller and easier to handle. Have you thought about getting one of the SDR dongles? Some types are not very expensive.

[banah]

Absolutely it would be nice playing with SDR. Maybe I'll do in further future..

At this moment I am more interested in catching real voices from radio station as I've imagined. If I use the 143Mhz it wouldn't possible to catch up the radio station, isn't it? 

It will have to be trial and error I think, though personally I don't think it is too critical (though some might argue otherwise). My antenna is horizontal and pointed just above the horizon in the general directionof the Graves transmitter. The recommendation, though, is to have the antenna in a vertical plane. One of the advantages of using 143MHz is that the antenna is smaller and easier to handle. Have you thought about getting one of the SDR dongles? Some types are not very expensive.

[The Admiral]

Have you Googled "meteor scatter" or "meteor burst communications"? That's more what you are seeking to do, rather than detect meteors per se.

[banah]

Thank you Ian, I am so grateful to your help. I found one youtube channel, it seems quiet close what I wanted. (Still I have no idea what's difference my system with his.)

https://www.youtube.com/channel/UCclhK0FGmlXSMTuogKGBIgg

I've sent some message, hope to hear something from there.

Have you Googled "meteor scatter" or "meteor burst communications"? That's more what you are seeking to do, rather than detect meteors per se.

[The Admiral]

One final thought. If you are going to hear short snatches of the broadcast programme, then the meteor reflection will need to last a significant time. During some occasional testing recently the number of 'long' events (i.e. greater than about 1 second) I've recorded over a period of 10 or 12 hours can be counted on the fingers of one hand, at most! Obviously, the odds increase dramatically during a meteor shower. So unless you are prepared to sit by your radio for a very, very long time  , you'll need to record these events somehow.