Meteor Detection with RTL-SDR

[wxsatuser]

LO is ok.

The wavy band is the 2.5khz bandwidth of the bottom waterfall, the passband.

You are sampling quite a bit of frequency in the top waterfall, zoom in a bit so the bandwidth is only about 5khz.
Then the 2.5khz passband should be in the centre, start frequency is the thin red line under the waterfall and the
blue column with horizontal bars is the passband.

This all depends on the dongle frequency, have you checked the offset, I doubt it will be on frequency.

[Stormchaser]

5 hours ago, wxsatuser said:

LO is ok.

The wavy band is the 2.5khz bandwidth of the bottom waterfall, the passband.

 

Thank you for the check and the clarification.

 

5 hours ago, wxsatuser said:

You are sampling quite a bit of frequency in the top waterfall, zoom in a bit so the bandwidth is only about 5khz.

Then the 2.5khz passband should be in the centre, start frequency is the thin red line under the waterfall and the
blue column with horizontal bars is the passband.

1

Yes, I usually am around 10 to 5 kHz bandwidth, I had zoomed back to show the curious 'waviness' of that particular signal in the general waterfall.

 

5 hours ago, wxsatuser said:

This all depends on the dongle frequency, have you checked the offset, I doubt it will be on frequency.

1

That's my problem since I cannot seem to get any kind of 2m beacon here (very strange, but I cannot manage to get signals from the usual beacons test after test) I cannot check the exact dongle offset. Going for the FM radios, they are spot on, but I had read that they're not a very reliable sign of precision.

I wonder if, since I am so far away from everything (as it seems ?) I should buy/build a better antenna with more gain, or put a couple/four of them in a pair/quad match to increase rx. I also thought about putting a LNA, but I don't know if it's worth since I have only 10 metres of coax between the antenna and the dongle.

Edited April 1, 2019 by Stormchaser

[wxsatuser]

What about trying an airband frequency, Stornoway tower is on 123.50mhz or may be a NOAA polar satellite, NOAA 19 is on 137.1MHz.
One of these may give an idea of the offset.

[wxsatuser]

post in wrong place ignore

Edited April 1, 2019 by wxsatuser

[Stormchaser]

4 hours ago, wxsatuser said:

What about trying an airband frequency, Stornoway tower is on 123.50mhz or may be a NOAA polar satellite, NOAA 19 is on 137.1MHz.
One of these may give an idea of the offset.

Great advice,  I didn't think to try with the satellites. They'll do, since the airport operates mainly when I'm at work. Let's see what will happen on the waterfall.

[The Admiral]

4 hours ago, wxsatuser said:

or may be a NOAA polar satellite, NOAA 19 is on 137.1MHz.

May be I'm wrong, but wouldn't a satellite suffer from doppler shift, unless it was geostationary? Don't know anything about NOAA!

Ian

[The Admiral]

5 hours ago, wxsatuser said:

Stornoway tower is on 123.50mhz

I believe the frequencies were changed last year. Stornoway Approach now uses 119.48MHz, ATIS is 126.7MHz. Not sure if the tower is still the same.

Ian

Edited April 1, 2019 by The Admiral

[Stormchaser]

2 hours ago, The Admiral said:

May be I'm wrong, but wouldn't a satellite suffer from doppler shift, unless it was geostationary? Don't know anything about NOAA!

Ian

Yes, they have this factor to consider, but using Orbitron in tandem with SDR# shoud do the trick in compensating for it.
Major problem is the fact that since my yagi is directional, at a certain point the satellite will simply disappear since I am not following it with a motor. Omni static antennae are definitely better, but that is another step in the future.

Thanks for the frequency correction for EGPO, I will do some trials in the coming days with both of them, to see if finally I will be able to see the dongle shift.

[The Admiral]

13 hours ago, Stormchaser said:

Thanks for the frequency correction for EGPO

Hmm, I'm not sure that they are correct either! Looking here the Stornoway frequencies for AFIS and Tower are seen to be the same figure of 119.48MHz, the same for approach too, which I find a bit odd. I'm confused, but this is a NATS site so it should be correct! However, there are other Scottish airports around which might also provide you with a fix. I doubt that the frequency offset will be more than a few hundred Hz out, so it shouldn't preclude you observing any meteors, in theory anyway. I think that they would be recognizable and always at the same frequency at the end of the trail, even if not spot on what you think is Graves.

I assumed that using satellites was to give a frequency fix, so I'm not sure how you'd do that if it is changing with time. Does this Orbitron thingy link into your SDR to sweep the frequency in sync, or does it just provide you with data? I suppose another venture would be to receive weather satellite images, if you don't already do that. Goggle brings up some useful sites I think. I found a couple ages ago, though never got any further than looking . See https://www.rtl-sdr.com/rtl-sdr-tutorial-receiving-noaa-weather-satellite-images/ and http://www.alternet.us.com/?p=1461 . If I'm not using SpectrumLab I have gravitated towards SDR Console in the past, and I see that has a satellite tracking tool, but I guess other SDR softwares do as well.

Ian

Edited April 2, 2019 by The Admiral

[The Admiral]

As an afterthought, you might be also able to receive the Scottish VOLMET (met broadcasts to aircraft in flight) on 125.725MHz, which should be continuous. I don't know where it's broadcast from though.

Ian

[Stormchaser]

On 02/04/2019 at 12:03, The Admiral said:

I assumed that using satellites was to give a frequency fix, so I'm not sure how you'd do that if it is changing with time. Does this Orbitron thingy link into your SDR to sweep the frequency in sync, or does it just provide you with data? I suppose another venture would be to receive weather satellite images, if you don't already do that. Goggle brings up some useful sites I think. I found a couple ages ago, though never got any further than looking . See https://www.rtl-sdr.com/rtl-sdr-tutorial-receiving-noaa-weather-satellite-images/ and http://www.alternet.us.com/?p=1461 . If I'm not using SpectrumLab I have gravitated towards SDR Console in the past, and I see that has a satellite tracking tool, but I guess other SDR softwares do as well.

Ian

6

Yes, Orbitron would give help in that regard, since having your position relative to the satellite (which is moving along the orbit) can aid in the calculations for the doppler shift and, connecting to SDR#, correct the frequency in real time.

 

Thanks for the links, I haven't managed to do something with them for now, between work and the usual Scottish Atlantic weather. However, taking a break yesterday morning, I think I managed to get the local airport VOR, at a nominal frequency of 115.100 MHz:

If this is indeed the VOR, then the dongle shift is not that much in the end, definitely less than what I had expected. As you can also see, my new AirSpy arrived too, and the difference with the previous dongle was evident since the first usage!

 

So, following this test, I put in parallel two instances of SDR#, one with my reception on the GRAVES frequency, and one from a receiver in southern England from the SpyServer Net on the same frequency. This last one got meteors, some decently big for the current period, but at the same time, no echo was registered from my local instrumentation.

I think that this means two or three things, after all the tests done yesterday:

1) my antenna is not enough to catch the echoes from this distance, so I need to buy a better one with more gain (or, possibly, two or four in an array);
2) the position of my antenna in the garden is not good enough, but since I cannot put it in a better location (like the roof) I need to pause this project and try again when I can:
3) or, simply, my distance is too much to get any echoes from that far away radar.

Would love to hear your thoughts, since probably I'm missing something somewhere. I'll continue with the tests when I can in the coming days/weeks, looking forward to a real test at the peak of the Lyrid meteor shower.

[The Admiral]

2 hours ago, Stormchaser said:

I think I managed to get the local airport VOR, at a nominal frequency of 115.100 MHz:

Well if you mean Stornoway, then I would think that it's very likely to be the VOR, if the information here is correct. And you appear to be only 150Hz adrift.

Looking at where you are situated though, and presumably not much above sea level, you are needing to look over the Cairngorms which rise to ~1300m, and I would guess that to see Graves will be a big ask. Though I'm no expert in such details, but in order to observe the echoes from over the South of France then you really need to see down to the horizon. The experts in long distance communication will no doubt be able to comment. Even if Graves back fires I think it might still be a tall order. If that's the case then Skyserver may be your only option.

As a matter of interest which Airspy do you have? I run a Funcube dongle and it would be interesting to see what improvement could be attained. When you say that the difference between the Airspy and your RTL-SDR was evident since first usage, exactly what did you find?

Ian

[Stormchaser]

3 hours ago, The Admiral said:

As a matter of interest which Airspy do you have? I run a Funcube dongle and it would be interesting to see what improvement could be attained. When you say that the difference between the Airspy and your RTL-SDR was evident since first usage, exactly what did you find?

1

Yes, with local I was talking about Stornoway airport, and checking around the fft profile seems to match what others have captured, so at least it's a nice confirmation of the system! 

Yes again, that's my main concern. I am really far away from the main detection zone (south of France) and even borderline from the northern lobes of the radar (northern France), unfortunately. It is also possible that, as I said, my antenna has not enough gain to capture what here could be faint echoes. Other tests are definitely required, otherwise, you are right, SpyServer Net could be an option.

I have bought an AirSpy R2 version, not the HF plus, and the first thing I noticed is the actual gain effect on the signal profile and the SNR difference between this and the old standard one. Just with the VOR, as an example, the other barely showed the two lateral spikes while this one made them evident since its first start. Another difference, at first glance, is how clearer the sound comes out compared to the other. Using the very same settings the AirSpy produces a much cleaner wave. Also, the AS unit doesn't become as hot to the touch.

I have had it just for a couple of days, but these are my first impressions. Not much, but I hope that they gave you an idea.

If I remember well, I think it was @BiggarDigger... that the software Spectrum Lab (in tandem with SDR# maybe?) is used to capture the screenshot of the meteor pings. Are there tutorials, or topics here on the forum, which can help me in learning to use this other program? How to setup the I/O between the two and such, and the grabbing part? Thanks! 

Edited April 5, 2019 by Stormchaser

[BiggarDigger]

Apologies, I've been out of circulation for a few days.

I don't think the gain of the antenna is a major part of the engineering problem when listening for GRAVES: the antenna I use is a simple 2 element phased array (an HB9CV design https://www.qsl.net/dk7zb/HB9CV/Details-HB9CV.htm) with forward a gain of 4dBd (around 7dBi).  Clearly the GRAVES radar transmits are very strong signal, so a 3 element yagi will do fine if you can see a main lobe common volume via line of site.  Your topographic profile shouldn't present much obstruction with a clear line of sight over water to the mainland.

The arithmetic however shows the forward lobes of the radar are well over your horizon, and for me too.  From other work, we have deduced there are likely to be reasonably strong rear facing lobes and sufficiently high angles for me to detect forward scatter in a northerly direction.  However my site is 350km further south than yours, which significantly alters the geometry of the common volume compared to that for Stornoway.  The maximum range to a 90km altitude is 1100km (line of sight) which, for you, is over Southern England and Northern France.  Although there appear to be rear facing lobes, I suspect these are not strong enough at the required angles to achieve echoes that are resolvable with entry level equipment at Stornoway.

Having now established your dongle is quite well tuned, you could try look for meteor scatter signals from GB3VHF.  Although this is running much lower power than the expected signal from GRAVES, that could be compensated for by increased gain in the receive antenna.  I wouldn't recommend stacking or baying antennas for 144MHz in the first instance: doing so poses real engineering challenges getting the phasing correct.  It will also significantly reduce the 3dB beam-width and place deep notches not far from the centre line of the antenna.  A small azimuth or elevation misalignment of the antenna could easily reduce the received signal dramatically. A modest single 9 element yagi (https://www.radioworld.co.uk/220309_tonna_2m_9_element_yagi_antenna_144_to_148_mhz) will give decent forward gain and broad beam width to be able to look for GB3VHF.  A mast head preamp could also be beneficial as the signal may be quite weak.

These should give a reasonable opportunity to receive meteoric signals from GB3VHF.  The challenge will then be to adjust the detection algorithms for take account the non continuous nature of the signal broadcast from GB3VHF.

To capture signals from GRAVES, I use SDR# and feed the audio into Spectrum Lab.  The primary reason for this is that Spectrum Lab refuses point blank to drive my dongle.  I suspect there is a non-standard build in my dongle firmware, but it's overcome by using SDR#.  To connect SDR# to Spectrum Lab I use a free virtual audio cable from https://www.vb-audio.com/Cable/.  This arrangement works well, even though SDR# uses more CPU than I would like.  There is an advantage to this method too: you are operating a configurable receiver via SDR# and can optimise parameters such as gain, bandwidths, noise blankers and notch filters using a much simpler GUI than through the configurations in Spectrum Lab.

Here's a screen grab of my SDR# configuration:

I now use a tweaked version of IanL's Spectrum Lab detection algorithm which gives good results for me.  Overall it works well, as can be seen with a satellite detection as I type:

 

My honest opinion, given what we know and/or have deduced about GRAVES, is that its south facing lobes will be too far away and well over the horizon from Stonorway. Any north facing lobes will be difficult to use at such extreme range and a closer north facing beacon such as GB3VHF may yield better results even if there are still limitations.

Richard

[The Admiral]

12 hours ago, BiggarDigger said:

Your topographic profile shouldn't present much obstruction with a clear line of sight over water to the mainland.

That's true, but once onto the mainland isn't the problem likely to be the 1000+ metre high Cairngorms 200km away? I haven't done the maths, but would you expect the radio waves to diffract over the top? Your location surely gives a better Southwesterly view I'd have thought. That said, is a higher gain antenna likely to help?

It looks as though there are some VOR beacons on Iceland that would be worth exploring, though their frequencies are around 100MHz. If you could get that to work it would open up a new avenue of interest!

Ian

Edited April 6, 2019 by The Admiral

[The Admiral]

13 hours ago, Stormchaser said:

Spectrum Lab (in tandem with SDR# maybe?) is used to capture the screenshot of the meteor pings.

 

12 hours ago, BiggarDigger said:

To capture signals from GRAVES, I use SDR# and feed the audio into Spectrum Lab.  The primary reason for this is that Spectrum Lab refuses point blank to drive my dongle.

That was one advantage of the Funcube, it would work straight into SpectrumLab, though as Biggardigger points out, it offers less control. Spectrum lab does have it's manual on line, but I confess I found it pretty hard going. A couple of years ago I would have been much more familiar with it, but time has erased much!

Ian

[Stormchaser]

13 hours ago, BiggarDigger said:

[...]

Having now established your dongle is quite well tuned, you could try look for meteor scatter signals from GB3VHF.  Although this is running much lower power than the expected signal from GRAVES, that could be compensated for by increased gain in the receive antenna.  I wouldn't recommend stacking or baying antennas for 144MHz in the first instance: doing so poses real engineering challenges getting the phasing correct.  It will also significantly reduce the 3dB beam-width and place deep notches not far from the centre line of the antenna.  A small azimuth or elevation misalignment of the antenna could easily reduce the received signal dramatically. A modest single 9 element yagi (https://www.radioworld.co.uk/220309_tonna_2m_9_element_yagi_antenna_144_to_148_mhz) will give decent forward gain and broad beam width to be able to look for GB3VHF.  A mast head preamp could also be beneficial as the signal may be quite weak.

[...]

My honest opinion, given what we know and/or have deduced about GRAVES, is that its south facing lobes will be too far away and well over the horizon from Stonorway. Any north facing lobes will be difficult to use at such extreme range and a closer north facing beacon such as GB3VHF may yield better results even if there are still limitations.

4

No worries Richard, and as always, thank you very much for your insight. Your posts are always a goldmine for information! Yes, at least now we know that the dongle works well, and works close to the frequency one needs to tune to. It was a good confirmation, finally.

Thank you for the antenna link and advice about that matter, I will think about it in the coming days and probably I'll take it after the Lyrid test, just to check every possibility at each step of the project.

I managed to connect SDR# and SpecLab successfully, the VB cable was easy to setup and now I'm playing with the (seemingly) infinite options that the software provides. Testing with an England SpyServer connection so I can easily see the GB3VHF beacon and work with it to familiarize with the program. I have read the guide for Ian's modified script, and it seems pretty straightforward, another thing to test in the coming days and weeks.

 

1 hour ago, The Admiral said:

It looks as though there are some VOR beacons on Iceland that would be worth exploring, though their frequencies are around 100MHz. If you could get that to work it would open up a new avenue of interest!

 

That would be an interesting thing to try indeed, also the beacon in the Faroe Islands which are directly above me, and definitely closer than southern England. Eh, always a lot of things to do, and the list grows more and more ?

 

1 hour ago, The Admiral said:

A couple of years ago I would have been much more familiar with it, but time has erased much!

 

Same problem here with my knowledge of French. When I was in Junior High I could speak it way better than English, but now, with the lack of practice, most of it has simply disappeared. A bit disconcerting if one thinks about it.

[BiggarDigger]

4 hours ago, The Admiral said:

That's true, but once onto the mainland isn't the problem likely to be the 1000+ metre high Cairngorms 200km away? I haven't done the maths, but would you expect the radio waves to diffract over the top? Your location surely gives a better Southwesterly view I'd have thought. That said, is a higher gain antenna likely to help?

It looks as though there are some VOR beacons on Iceland that would be worth exploring, though their frequencies are around 100MHz. If you could get that to work it would open up a new avenue of interest!

Ian

The range to the hills from Stornoway shouldn't give rise to too many issues.  The signal propagating from the reflection media will have been refracted and dispersed through the ionosphere and troposphere already.  The may be some additional distortion, but the Scottish mountains are generally flat topped rounded hills (and quite wet most of the time too!).  It's possible more bifurfication of the signal could occur however. 

The Icelandic VOR beacon is a very interesting proposition.  The beacon at Akureyri is on 113.6MHz which is a nice frequency to use for meteor detection as it will scatter well.  It's radiation pattern is ideal for these purposes and, additionally, it's a good range being approximately 1100km, which is a magic number in this context.  It means you will be able to see a 90km altitude at Reykjavik on your horizon and a forward scatter common volume will exist all the way from your horizon to your zenith, giving you a large reflecting media to capture incoming meteors.

A broad beamwidth vertically polarised antenna pointing northwest from Stornoway should have a decent chance of detecting meteoric reflections from that beacon.

You will undoubtedly have interference from auroral scatter which will lead to blurring.  Auroral scattering will be quite prevalent at your latitude, but auroral scattering is fairly wide wideband and quite different to the narrowband meteor scatter you are looking for.  Audibly the narrowband Morse or voice signal will be blurred into a broad hissing noise.

Even though your current antenna is tuned to approx 144MHz, it may be worthwhile turning the antenna to the northwest and see if you can hear that beacon via the Aurora, taking into account auroral forecasts and timing it to an increase in auroral activity.  We are close to sunspot minimum, but there are still plenty of visual Aurora reported visible from Skye and other northern locations.  If you can hear the beacon via Aurora, ther is a very good chance of obtaining meteor reflections off it.

I would be tempted to look for it myself, but my antenna is mounted on the SouthEastern side of the house and totally blocked to the NorthWest.

Richard 

[Stormchaser]

4 hours ago, BiggarDigger said:

The range to the hills from Stornoway shouldn't give rise to too many issues.  The signal propagating from the reflection media will have been refracted and dispersed through the ionosphere and troposphere already.  The may be some additional distortion, but the Scottish mountains are generally flat topped rounded hills (and quite wet most of the time too!).  It's possible more bifurfication of the signal could occur however.

[...]

I would be tempted to look for it myself, but my antenna is mounted on the SouthEastern side of the house and totally blocked to the NorthWest.

Richard 

3

Very interesting Richard, but for me too that direction is precluded, I have other houses towards NW, it's a problem even if I want to try and take low aurora city shots, too high on the horizon (the fact that I'm a bit downhill definitely doesn't help), but I will consider it if/when I will be able to relocate to a household in a better position for these trial-and-error tests.

However, I have a bit of news, I managed to get everything working, and while I was monitoring today with both SDR# and SpecLab... I got this!

Now, SDR# didn't show anything at the time, while SpecLab plotted this. I don't want to say it... but I have to ask. Could this be a meteor echo?

I was on the GRAVES frequency, following the transit of the ISS (but that didn't appear on the screen) and after a couple of minutes this appeared... what do you all think?

[The Admiral]

Well it does look like a meteor! It would help though if there were some axes of the chart included. I assume for example that the RHS is the higher frequency side. What is the scale? Given that the ISS is about 4x higher than typical meteor trails I would have thought it might have been more visible (though perversely I've not found this to be true in practice, the meteors can can give a lot more signal). What time was the expected transit? I don't think the 13.24 pass would have been good, and the 16.34, 18.11, and 19.48 too far north of Dijon unless there are significant rear lobes. So that just leaves the 14.58 as a potentially viable one. And the next one at 21.25. I suppose you didn't have the Spyserver running from the south of England to correlate it did you?

Ian

Edited April 6, 2019 by The Admiral

[Stormchaser]

17 minutes ago, The Admiral said:

Well it does look like a meteor! It would help though if there were some axes of the chart included. I assume for example that the RHS is the higher frequency side. What is the scale? Given that the ISS is about 4x higher than typical meteor trails I would have thought it might have been more visible. What time was the expected transit? I don't think the 13.24 pass would have been good, and the 16.34, 18.11, and 19.48 too far north of Dijon unless there are significant rear lobes. So that just leaves the 14.58 as a potentially viable one. And the next one at 21.25. I suppose you didn't have the Spyserver running from the south of England to correlate it did you?

Ian

Sorry, in the excitement I cut the scale on top. The meteor was on the 1100 Hz mark, with a scale starting from 0 on the left to 2200 Hz on the right. On the left side there would have been the timing marks, the usual hh:mm:ss.

For the ISS, the time was the 19:48 one indeed, I had n2yo open to monitor it, but it was indeed in the wrong position now that you point it out the fact. I will try again tomorrow, with better transits and a SpyServer running to compare, but if this is a meteor is great news! 

Edited April 6, 2019 by Stormchaser

[wxsatuser]

Looks like a ping.

I spent a couple of hours this morning monitoring GRAVES.
Quite a few meteors, some EME returns and some strong tropo.

Will sort out some screen shots tomorrow.

[The Admiral]

47 minutes ago, Stormchaser said:

if this is a meteor is great news! 

Indeed, I feel your excitement! What makes me think it is, is because there is a sharp descending frequency transient, with a more intense region at the end. With bigger meteors, the intense region will extend along the time axis at the Graves (zero Doppler) frequency, to give the appearance of a hook. But I'm sure you know this. You are most likely to see those during the meteor showers. It'll be interesting to see how frequent you see them, and how they compare with measurements made from the South of England. 

It would still be interesting to try VOR stations that you are able to get aligned to. I suppose the problem then might be to see meteors along with the background carrier. That leads me to wonder if you could point your antenna much higher in the sky so that the sensitivity to the direct path is reduced, and maximise reception of backscatter. After all, some professional monitoring sites have the transmitter and receiver co-located. Just a thought.

Ian

PS. I use Heavens Above https://www.heavens-above.com/PassSummary.aspx?satid=25544&lat=47.322&lng=5.0415&loc=Dijon&alt=249&tz=CET centred on Dijon, and on the 'ground track' tab, with a result like this

I find it easy to interpret, but need to be aware of the time difference between Dijon and here. But, each to his own.

Edited April 6, 2019 by The Admiral

[BiggarDigger]

Certainly does look like a meteor.  Well done, congratulations!

It's difficult to completely interpret without time and frequency scales, but the apparent Doppler shift of the head followed by the intense body is classic meteor.

That's encouraging to see.  Hopefully you get a few recorded events overnight when the background rate peaks.

Richard 

[Stormchaser]

Thank you all! It's fantastic news ?

Unfortunately last night my rickety old pc froze, so no detections, but now it's running again and let's hope for something in the coming hours/days. When I'll manage to get something else I will post a complete screenshot, so it will be easier to decode for you all.

Crossed fingers also for the Lyrids at the end of the month, there should be something good during the peak hours, even from this far away.

@The Admiral Thank you for the HA link, I use that one too, it's the best to keep track of future passages, together with n2yo for the real-time tracking (or Orbitron too for the same purpose).