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Stormchaser

Meteor Detection with RTL-SDR

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Good morning everyone,

since some time ago, when I started tinkering with my Raspberry Pi board and company, I became interested in trying to capture meteors using the GRAVES radar in France. 

I bought myself, to start, a R820T2 RTL2832U 1PPM TCXO SMA RTL-SDR dongle, (picture here) with a YG27 35 Dual Band HI Spec 2/70cm Yagi Antenna (picture here) connected with an RG58 coax cable.

Then I started tinkering with the raspberry, and I managed to make a couple of spectrum-showing software to work, after making the board recognize the dongle. This was around a couple of weeks ago, and I wanted to wait to see if the general system would be able to work 24/7 without too many problems. Luckily, the performance of the little RasPi board is excellent in that, and the results were positive.

Now I am starting to see if the rx part works as well, and reading many topics here on the forum, I saw that many of you have successfully managed to detect meteors, even big ones, with similar equipment. Since this is the part where I am not really familiar with, I wanted to ask a couple of questions, which I hope you can help me with.

1) I tried receiving the GB3VHF beacon attaching the dongle to my laptop with HDSDR software on, to try and see if everything I've built was good, but (possibly or surely because I didn't set it properly) I cannot manage to obtain a strong signal out of the bg noise like some images I've seen here on the forum. I will attach a screenshot of what I can see. Is there something wrong somewhere? Can someone list their setup data for me to compare them? I have also SDRSharp to work with if needed.

2) When I tried to tune to the GRAVES frequency, unfortunately I didn't manage to catch anything, but doing the disconnect the antenna and test the dongle alone trial, I can tell that the antenna is receiving something. Do I have too much interference around and maybe I need some kind of filters along the rx pipeline?

3) Really, any kind of advice is more than welcome, since I'm just starting. My antenna is naturally outside, with a clear view towards Dijon, around 4 metres high above the ground, with 10m of cable (approx.) between her and the dongle. I am located, as you can see from the profile, in Stornoway, around 1700km away from the radar detection zone if my measuring is correct.

Thank you for all the assistance I'm sure you will be able to provide! If you need any other info about my system to help, feel free to ask! 

73 from IZ6GSM

 

image.png

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Posted (edited)

You have the LO at the RX frequency, may be better to move it away a bit.

GB3VHF runs about 30watts split between two antennas, one does beam approx your way but
would be surprised if you could hear it unless conditions were up.

Mike G1HWY

Edited by wxsatuser
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2 hours ago, Stormchaser said:

2) When I tried to tune to the GRAVES frequency, unfortunately I didn't manage to catch anything, but doing the disconnect the antenna and test the dongle alone trial, I can tell that the antenna is receiving something. Do I have too much interference around and maybe I need some kind of filters along the rx pipeline?

Well of course you shouldn't be able to see a cw signal direct from Graves, only a meteor scatter signal as and when it occurs. Outside of meteor showers you may have to wait many minutes before getting a 'ping'. As wxsatuser suggests, one normally sets the 'tuned' frequency 1-2kHz away from Graves in order to make the scatter audible. You are a long way from Graves as well, so it will be interesting to see what can be detected.

Ian

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1 hour ago, wxsatuser said:

You have the LO at the RX frequency, may be better to move it away a bit.

GB3VHF runs about 30watts split between two antennas, one does beam approx your way but
would be surprised if you could hear it unless conditions were up.

Mike G1HWY

Thank you Mike. I knew that there was something that didn't add up in the whole thing.

Playing a bit with the software I managed to firstly do what you said, and secondly to hear something very faint in the background. No visible sign of the alternating sound pattern like some images here on the forum on the spectrum (screenshot attached) but listening to it for a bit seems to give the idea of morse code, even if I cannot precisely discern the letters/numbers. It seems cyclical though, so possibly it's a confirmation that the system works.


image.thumb.png.9c6705027064158c4b1e384e5d7b1cb2.png

 

Is there another way to check (possibly with another beacon?) if my system is effectively receiving something? I tried (second screenshot) with our local FM radio and I'm getting a good signal, so I want to think that I assembled everything appropriately...

image.thumb.png.91f0b130f88e2fee13e0f14a81461f2b.png

 

1 hour ago, The Admiral said:

Well of course you shouldn't be able to see a cw signal direct from Graves, only a meteor scatter signal as and when it occurs. Outside of meteor showers you may have to wait many minutes before getting a 'ping'. As wxsatuser suggests, one normally sets the 'tuned' frequency 1-2kHz away from Graves in order to make the scatter audible. You are a long way from Graves as well, so it will be interesting to see what can be detected.

Ian

Thank you for the info Ian! I was imagining something like that, but thanks for the confirmations.
Exactly, that was mainly why I am doing this little tinkering of mine (adding also the testing of the RasPi in these conditions). Will I be able to see only the bigger meteors? Or maybe even some smaller one? Or nothing at all?
I am also looking forward to the ISS transit of this evening over Dijon, to see if it will be visible on the spectrum.

 

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As has been noted, you'll be  too far north from GB3VHF to receive tropospheric ground waves unless there is ducting underway.

You may detect meteor echoes from it however.  Many years ago, I would often hear echoes from the now defunct Lerwick beacon from my (then) site in central England, without tropo ducting.

Your range to GRAVES is pretty extreme.  I have postulated elsewhere that there may be significant rear lobes from the radar as the geometry requires forward scatter off rear lobes from the radar to be able to detect a signal at my location near Biggar and I am some 350km south of you.

Remember, your range to Dijon is just the start. You need to be able to see a common volume of the sky at about 95km altitude.  For south facing lobes this would be over Iberia, southern France, Italy, the Aegean Sea, northern Balkan states etc.  I suspect these areas will be over the horizon from Stornoway,  so it will be very interesting to see what signals you detect off any north facing lobes, which would be over the Channel and southern England.  Detection of these signals will provide further evidence of significant rear lobe radiation.

I would ensure the antenna is pointing at the horizon to maximise the chance of illuminating the common volume of the sky.

My antenna is a simple HB9CV 2-element phased array, with around 10m of RG58u coax feeding an RTL-SDR and achieves good results.

There's not much shower activity just now, so you'll need to rely on background rates, which peak in the early hours of the morning.

Try tuning to somewhere between 143.048 to 143.049MHZ on USB, depending on the accuracy of your SDR.  That should give you sufficient offset to see echoes at around 1 to 2kHz.  My SDR is tuned to143.048850MHz USB and yields 1.2kHz baseband echoes.

Good luck,

Richard

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Richard, this was a mine of information for me to elaborate on! 

I did some volumetric simulation of the sky and even this far north I should be able to see around 85% to 95% of the common sky reached by the GRAVES, so in that sense, I should be ok. My antenna is already pointed towards the horizon, which the only obstacles are the hills of the mainland, but they occupy an area of around 1 to 2 deg in elevation, so they should not pose a problem either.

I've now tuned my HDSDR to those frequencies, leaving a bit of bandwidth open for any accuracy discrepancies, I think that now all that's needed is to wait and see.

Thanks again!

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Did you detect the ISS pass this evening?

The pass at 19:24 was detected here at the extreme range:

event20190323_192500_294.jpg.3961ae82a917849573506c0f7a5b4900.jpg

The zero radial Doppler shift occurred at 19:24:18, which corresponds to the the ISS at the maximum elevation according to Heavens above:

PassGTrackLargeGraphic.aspx?satid=25544&date=58565.808542&lat=55.6234&lng=-3.524&loc=Biggar&alt=215&tz=GMT

The footprint here is where the ISS is 10° above the horizon, which should still be above your horizon in Stornoway and hence should be detectable.

 

I'm interested in understanding more about your meteor common volume simulations.  If my arithmetic is correct, the 95km altitude range is ~1100km with the antenna pointing at the horizon.  Perhaps a badly drawn sketch may help explain my arithmetic:

image.png.308258e1b50a9e61d9caca64abded62e.png

Therefore, to receive meteoric reflections from a common volume 95km above the surface of the Earth, that common volume should be approximately 1100km distant.  There will be some blurring in this as the GRAVES radar signal is not uniform and the scattering media not constant, but it will do for approximations I think.

Normally, expected ranges for forward scatter is up to ~2200km where both stations are pointing at each other and the common volume bisects them.  However, that is not the commonly accepted position for GRAVES which, based on articles and photographs of the site, illuminates a semi circle from West through South to East.  If this commonly accepted position is correct, we are receiving backscatter echoes from south of the site.  However, that would be outside the 1100km range to the common volume from my site.

My contention is therefore that there must be significant rear lobe radiation at sufficiently high angles to illuminate the sky over northern France in order for me to receive meteoric reflections.

It follows that for your site at Stornoway, the common volume would be over Southern England and the English Channel and definitely require significant rear lobe radiation.

Have you seen any meteor echoes yet, as these would be very interesting at such range.

Richard

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16 hours ago, Stormchaser said:

Thank you Mike. I knew that there was something that didn't add up in the whole thing.

Playing a bit with the software I managed to firstly do what you said, and secondly to hear something very faint in the background. No visible sign of the alternating sound pattern like some images here on the forum on the spectrum (screenshot attached) but listening to it for a bit seems to give the idea of morse code, even if I cannot precisely discern the letters/numbers. It seems cyclical though, so possibly it's a confirmation that the system works.

Is there another way to check (possibly with another beacon?) if my system is effectively receiving something? I tried (second screenshot) with our local FM radio and I'm getting a good signal, so I want to think that I assembled everything appropriately...

 

 

You could try and receive the GB3VHF JT65B mode which is a very weak signal mode.

The beacon keys like this.
At the start of every even minute it will key JT65B for 48secs.
At the start of every odd minute it will key CW for 13secs and then at 30secs it will reverse the phase of the carrier until the new even minute.
This reversal sounds like ticking, a 1bit/sec pattern of 101010.

Have just checked and it is keying this system at the moment.
The JT65B can disappear if the beacon loses GPS lock but is replaced with morse until lock is re-established.

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1 hour ago, wxsatuser said:

You could try and receive the GB3VHF JT65B mode which is a very weak signal mode.

The beacon keys like this.
At the start of every even minute it will key JT65B for 48secs.
At the start of every odd minute it will key CW for 13secs and then at 30secs it will reverse the phase of the carrier until the new even minute.
This reversal sounds like ticking, a 1bit/sec pattern of 101010.

Have just checked and it is keying this system at the moment.
The JT65B can disappear if the beacon loses GPS lock but is replaced with morse until lock is re-established.

Thank you for the advice Mike, I am trying this right now but the rx this morning is way more disturbed than yesterday, so I will be waiting for a better time to listen to this weak signal. It's a bit of a problem being this far away from a stable reference, but we'll manage to overcome it in time.

I've tried with the local FM radio, I know that it's not a precise method, but since it gave me quite the difference from the declared frequency I want to be sure that my dongle is properly tuned because otherwise, I would just waste time looking at a screen that doesn't show what it should in the place that it should be.

 

11 hours ago, BiggarDigger said:

Did you detect the ISS pass this evening?

The pass at 19:24 was detected here at the extreme range:

The zero radial Doppler shift occurred at 19:24:18, which corresponds to the the ISS at the maximum elevation according to Heavens above:

The footprint here is where the ISS is 10° above the horizon, which should still be above your horizon in Stornoway and hence should be detectable.

I'm interested in understanding more about your meteor common volume simulations.  If my arithmetic is correct, the 95km altitude range is ~1100km with the antenna pointing at the horizon.  Perhaps a badly drawn sketch may help explain my arithmetic:

[...]

My contention is therefore that there must be significant rear lobe radiation at sufficiently high angles to illuminate the sky over northern France in order for me to receive meteoric reflections.

It follows that for your site at Stornoway, the common volume would be over Southern England and the English Channel and definitely require significant rear lobe radiation.

Have you seen any meteor echoes yet, as these would be very interesting at such range.

Richard

4

Hello Richard, thank you for your very helpful insight! I managed to reach your conclusions and I discovered an error in my calculations done yesterday. I've redone them this early morning and I thank you for confirming my result: I applied reverse reasoning, being, how much horizon could I see if I was anywhere but at 95km of altitude above ground, and my result is 1104.9km (so pretty in line with yours).

So, to reach the common volume, with my antenna pointing at 0 degrees elevation (horizon) this is my distance. I tried looking for the ISS yesterday (btw great capture for you!) but I didn't manage to see it. It could be, however, that since from my position the space station was below the horizon, I could not see any signal reflection. For me the southernmost transits that can be seen are the ones transiting well over the GRAVES (just shifting the lines around 300km nnw of your position in terms of above horizon elevation, so I want to check this fact too. And also, since I've seen that it can be done, to see if when the moon is in the common sky area, I can see some echoes from that, but this will need to wait for next lunation.

I agree completely with your conclusion on my situation, and no, unfortunately I still didn't manage to get any meteors. I left my Echoes sw working overnight, but it got just false positives. However, as I wrote to Mike, I firstly want to be certain that the tuning is correct, otherwise I will be only looking at the wrong part of everything, and definitely waste time. However, I'll try again for the ISS transit tonight, while working on the tuning aspect.

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18 minutes ago, Stormchaser said:

I tried looking for the ISS yesterday (btw great capture for you!) but I didn't manage to see it. It could be, however, that since from my position the space station was below the horizon, I could not see any signal reflection. For me the southernmost transits that can be seen are the ones transiting well over the GRAVES (just shifting the lines around 300km nnw of your position in terms of above horizon elevation, so I want to check this fact too. And also, since I've seen that it can be done, to see if when the moon is in the common sky area, I can see some echoes from that, but this will need to wait for next lunation.
 

ISS would have had a max elevation of about 6degrees and a range of 1770kms from you.
Peak elevation would have been around azi 140degrees but it would be eclipsed about 1minute after peak elevation.

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I think you're correct in your approach: setup the tuning first so you have echoes, either from ISS or meteors, then look at your detection software.  All things being equal, the ISS would have been detectable from your site last night, being only 3 or 4 degrees lower than for me.

Perhaps experiment with Spectrum Lab and the published scripts to correlate against your Pi software.

Bear in mind, the majority of echoes I recieve out of shower peaks are very short duration (between 0.1 and 0.5 seconds) and may be almost inaudible, so you may need some form of automated logger to see them just to get the tuning right.

Take heart though, even though your range to GRAVES is extreme, you may still receive signals.  If there is backfire radiation illuminating a common volume north of the site providing the path for the signals that I detect, it follows there is a good chance you may have a similar path.

If GRAVES turns out to be too far over the horizon for you then wxsatuser presents an alternative of using GB3VHF, which is radiating in your direction, albeit with less ERP.

Richard 

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Yes, I want to be sure that my tuning is exact before looking at the screen for something that isn't there to start with ?

For now I am fully experimenting with my laptop, since the operations are smoother with more processing power. As soon as I will receive a good confirmations that everything is ok, I will go back to the RasPi and see if I need to adjust something on that too. A bit of a long process but a fun and challenging one.

I got an online SDR which streams GB3 constantly, so as soon as I'll manage to detect it I will be able to check where the correct frequencies are. I'll keep everyone updated as soon as I have news on my system.

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Short range MS to GB3VHF could be possible as Richard points out.

Going back around 20 years a go we used to work a survey ship, forget the callsign, but it was relatively easy to
work on 144MHz while sailing around the top of Scotland and top of the North Sea.
Always worked it around 4>6am here on the south coast.

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5 hours ago, Stormchaser said:

I got an online SDR which streams GB3 constantly, so as soon as I'll manage to detect it I will be able to check where the correct frequencies are. I'll keep everyone updated as soon as I have news on my system.

 

Little update, I used a couple of hours without rain this afternoon to check the hardware part, so far I found that the cable was not transmitting well, so I redid the connections from scratch. The multimeter test now goes smoothly in indicating that there are no shorts, so it should tx without problems.

Tested again on two FM signals with broad bandwidth, the Isles radio here in Stornoway at 103 MHz and the BBC Gaelic at 104.5 MHz and the output is strong and clear, discernible without too much interference (or none at all), and the tuning is centered on the declared frequency.

Tried then on the GB3VHF, but nothing, comparing it to the online stream I cannot seem to manage to see it on the spectrum, as you have theorized, so I'm basing my dongle precision on the FM radios for now.
Waiting for the transit of the ISS over the GRAVES area this evening at 18:25 pm approx, let's see if it will be possible to see it.

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Today's update. More hardware testing, brought down the antenna, checked the connectors and brought it up again, all seems to work fine, so at least from that side, I'm sure of the equipment.

Went back to the software part, HDSDR in the case, and there has been a nice reduction of the overall noise floor level, so this should be another point to the fact that everything seems to work well. Went around on the FM channels and no problems there, but I still didn't manage to get any of the VHF beacons to check my tuning, so for now, I resolved in increasing my detection span in the Echoes software, that should be enough to compensate if the shift is not too big.

Listened all afternoon and got some morse streams onto the 2m band, some fainter than others, but still discernible in their pattern, stops and restarts so that should be another positive mark in the logbook.

 

Now I think that the only thing I can do, after having set up everything again on the RasPi, is waiting with fingers crossed that the system will see some meteors. I think I'll wait until the Perseid shower in August to see how this experiment goes, and then decide from the results if there is something to be done to improve it or scrap it because the location is not a favorable one for this kind of detections (sure hope not, I definitely want to see something on my screen! ?)

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The detection of Morse signals on 144MHz amateur band is encouraging. You could take a look for specific beacons listed here: https://www.microwavers.org/maps/2m.htm to see if you can identify the station and use that as to verify the SDR tuning accuracy.

Background meteors will peak in the Lyrids shower on the 23rd April which should give a good indication of any possible common volume for GRAVES or even GB3VHF as the transmitter station.

Richard 

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While working today I was thinking a bit regarding using radio beacons (like GB3VHF) to try and receive some meteors, like GRAVES. Is it possible in the first place or it's just a wrong reasoning direction?

If the answer is that something along this thought-line is possible, then if the beacon is always transmitting something (visible on the spectrum) how would it be possible to recognize (visually) a meteor pinging in the waterfall? (I imagine that it would be easy to hear its sound)

I wanted to try with the OY6BEC beacon in the Faroe Islands, which is directly above me towards the north, and we share a large common volume of sky adapting the same calculations that we discussed. I haven't managed to find if the antenna was omnidirectional or not, but I found a video on YT with someone that received its signal from Cornwall, and since Cornwall is directly south of my position, I am assuming that I should be able to do it too.

This is the info page for more details: https://www.qrz.com/db/OY6BEC

 

So, just this thought, but I was curious to hear your opinions on the matter.

In the meanwhile, (unfortunately) still no detections at all from the GRAVES frequency.
 

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Here is GRAVES comes and goes sometimes for long periods, what mode I'm not sure as the direction is not to good for me.
The slanting diagonal line is ISS and if you look at the direct signal there are little lines at right angles around the third time line down.
These are pings that are easily audible on  my IC7100, the right hand continuos signal is a birdy.

ISS.jpg.7b3a68743bba10a2f7ae78886691180a.jpg

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Posted (edited)

GB3VHF isn't a continuous carrier, there are short breaks and periodic morse, and there is a period of frequency modulation. These are described on the GB3VHF website. So it might not be ideal, and of course it may not be beaming much skywards or with enough power (only 30w). The only thing is to try using the beacons and see! In the past the non-digital TV broadcasts could be used, and there are a few stories from the States describing that, IIRC. But of course they were quite powerful transmitters. 

Some use the Belgian transmitter BRAMS, but that operates at around 50MHz.

Ian

Edited by The Admiral
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It is possible to use amateur radio beacons for meteor detection.  In the past, I used to operated amateur meteor scatter and would often hear signals from such beacons.

However as has been noted, amateur beacons are typically low power and illuminate smaller volumes of the sky.  Reliable detection of signals from these beacons may need higher gain antennas.

The non CW nature of these beacons does mean you may miss a number of incoming meteors, including the head echo of long duration events.  But if your range to GRAVES is too far, they are an alternative worth trying.

Richard 

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Posted (edited)

Mmm, definitely food for thought then, thank you all! I may do some trial and error test in these days, since the weather will give good conditions to stay outside and operate the antenna.

Another chance I wanted to try (but as stated, I would need a 50MHz antenna) was the BRAMS radar down in Belgium, since it's around 300 km nearer to my position. Do we know if the emission geometry pattern is like the GRAVES or a different one?
Because if there is some north-west-bound lobe, I could have more positive results in tuning to that one, since it will definitely be above my horizon in a better position compared to the French system (surely more common sky volume). The distribution of the receiving stations in the nation seems to suggest something akin to a circular irradiation pattern, but I didn't manage to find any relevant info on that.

Was thinking also to buy an AirSpy SDR instead of the normal dongle I'm using, but that's for the future evolution of the project.

Edited by Stormchaser

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10 hours ago, Stormchaser said:

Do we know if the emission geometry pattern is like the GRAVES or a different one?

Have a look at this document found on the Britastro site.

BRAMS_Meteor_Radar.pdf

Ian

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3 hours ago, The Admiral said:

Have a look at this document found on the Britastro site.

BRAMS_Meteor_Radar.pdf 2.29 MB · 1 download

Ian

I didn't know how I managed to miss that, it's even in the first page of google!

Thank you Ian, much appreciated! I'll read it today after work, let's see what we can do about it.

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Definitely an interesting read, also for all the various rx stations over the nation, they created a nice detection grid for this project.

This evening I tried to see if I could manage to detect an ISS pass which should have been in the correct position for an eventual northern lobe in NW France, as theorized and talked multiple times on this forum and even in this topic. Unfortunately, no success, so before trying something else, I wanted to post the configuration I'm using now for HDSDR, could you please check that everything is set up correctly?

In the ExtIO Panel these are the values:

image.png.40143d63a25a2eaf3a007becfe025b8a.png


While in general, the waterfall today looks like this (on the far right, the LOA frequency).

image.thumb.png.4d8201a2b02342edab10cf9351a27790.png

It's the first time today that that fuzzy band has appeared around the GRAVES frequency... am I correct in assuming that it is some unwanted bg noise? It varies quite rapidly sometimes, going from 143048 to 143053 as a center column and swaying side to side. What could that be?

Also, how much the LOA and the Tune frequencies have to be different? Is there a normal reference (like always x Hz for band y) or can it be completely custom?

All the rest seems ok, but it's never bad to crosscheck everything, especially if you experts have further advice for me. Thanks again!

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