Meteor detecting

[Geoff TheasbyParticipant @geofftheasby]

Yagis need pointing, but at what? The radiant won't help because that's where the meteors 'seem' to originate, but are actually seen at widely separated angles. The gain provided by a yagi is not really necessary as the signals are generally strong enough. A turnstile needs no directivity.

Pointing the yagi upwards by 10 or so degrees minimises signals from terrestrial sources in that direction. You need a vertical polar diagram to show this, rather than the usual horizontal polar diagram, which shows the gain pictorially using the aerial location at the centre.

[Geoff TheasbyParticipant @geofftheasby]

I forgot to add, simple meteor detection works better at lower frequencies, below 150 MHz.

Geoff

[Neil WyattModerator @neilwyatt]

Posted by Geoff Theasby on 20/06/2018 14:03:15:

Yagis need pointing, but at what?

The Graves radar in southeast France!

It's a 180-degree wide array they use to plot the orbits of satellites, it's beamed up at the sky which is why it works well.

Greater gain gives a different profile for detections – more smaller ones from a narrower area. As the number increases exponentially as they get smaller you get more hits by looking at a smaller area with greater gain.

You (or someone) asked about the ISS, I got a much better return of it today. Next challenge will be to get ISS slowscan TV the next time they do a demo. It's transmitted at 145.8MHz using a hobbyist 25 watt Kenwood transciever!

[doubletopParticipant @doubletop]

Posted by Neil Wyatt on 20/06/2018 19:00:42:

Posted by Geoff Theasby on 20/06/2018 14:03:15:

Yagis need pointing, but at what?

The Graves radar in southeast France!

It's a 180-degree wide array they use to plot the orbits of satellites, it's beamed up at the sky which is why it works well.

Greater gain gives a different profile for detections – more smaller ones from a narrower area. As the number increases exponentially as they get smaller you get more hits by looking at a smaller area with greater gain.

You (or someone) asked about the ISS, I got a much better return of it today. Next challenge will be to get ISS slowscan TV the next time they do a demo. It's transmitted at 145.8MHz using a hobbyist 25 watt Kenwood transciever!

 

Pointing Yagis – The Graves Radar has an elevation beam width of 25deg pitched up at 15deg. The latitude of Dijon is 47degN and by way of example Northampton is 53degN

 

If the Rx Yagi also had a beam width of 25deg then the pitch up should be around 13deg so 10deg would be OK as the elevation beam width would certainly be greater than 25deg as it needs to be 180deg in azimuth. There is something to be said for a better shape to the RX antenna polar diagram. Now if you were to have a 4 element array that stepped in sync with the Graves azimuth sweep….

 

ISS – The ISS plot is interesting as it has a greater doppler shift than the meteor returns. With such a strong return from a target that isn't breaking up on entry is interesting as it has similar characteristics to the meteor return that is allegedly breaking up.

The ISS return also has those faint spectral lines how are they explained? There are also the lines at 143,046,800 143,048,900 and 143,052,900 something in the receiver?

Like Dave this is becoming an interesting distraction, particularly as I have no chance whatsover of reciveing these signals from New Zealand.

Pete

 

Edited By Doubletop on 20/06/2018 21:40:56

[doubletopParticipant @doubletop]

An interesting document

https://britastro.org/radio/projects/Detection_of_meteors_by_RADAR.pdf

 

Pete

Edited By Doubletop on 21/06/2018 06:34:02

Edited By Doubletop on 21/06/2018 06:34:40

Edited By Doubletop on 21/06/2018 06:35:00

[SillyOldDufferModerator @sillyoldduffer]

After nothing all morning I heard an echo lasting a couple of seconds at 9:36 GMT. Apart from that very little. I watched the background noise come up with the sun (proving it must be daylight!), and saw my main computer generate some spurs as it booted. Once it's running they mostly disappear. Listening to white noise is torture.

Thanks to doubletop for the link to Dr David Morgan's pdf – very informative.

For 'mislaid parts' reasons my turnstile is a dipole about 6 foot off the ground. Needs more work!

Dave

[Neil WyattModerator @neilwyatt]

Posted by Doubletop on 20/06/2018 21:39:23:

ISS – The ISS plot is interesting as it has a greater doppler shift than the meteor returns. With such a strong return from a target that isn't breaking up on entry is interesting as it has similar characteristics to the meteor return that is allegedly breaking up.

The ISS return also has those faint spectral lines how are they explained? There are also the lines at 143,046,800 143,048,900 and 143,052,900 something in the receiver?

The meteor doesn't 'break up' it 'ablates' generating a trail of ionised plasma.

Extended meteor trails show diffraction patterns as they are extended targets.

The spectral colours just show changing intensity. The pulsing of the ISS trail is due to the phased scan of the Graves Radar. Note the timescale is probably different from the meteor plot.

Clearly some meteors may be missed by falling between graves pulses.

The vertical lines are probably radar transmitters, that at 143,048,900 is probably the back signal from Graves itself, allowing for a small error in receiver calibration, the others being ATC?

[Neil WyattModerator @neilwyatt]

Posted by Doubletop on 21/06/2018 06:33:33:

An interesting document

**LINK**

Pete

Yep. I've read that three times in the last week!

[doubletopParticipant @doubletop]

Posted by Neil Wyatt on 21/06/2018 21:19:03:

The meteor doesn't 'break up' it 'ablates' generating a trail of ionised plasma.

Extended meteor trails show diffraction patterns as they are extended targets.

The spectral colours just show changing intensity. The pulsing of the ISS trail is due to the phased scan of the Graves Radar. Note the timescale is probably different from the meteor plot.

Clearly some meteors may be missed by falling between graves pulses.

The vertical lines are probably radar transmitters, that at 143,048,900 is probably the back signal from Graves itself, allowing for a small error in receiver calibration, the others being ATC?

Thanks Neil

Somewhere in the thread somebody had suggested the meteors would break up, which I wasn't too sure about but if it had been the case then ISS and meteor signals would be markedly different.

The thing I have been trying to reconcile is the faint diagonal lines in your plots that are changing frequency over time. The examples in Dr David Morgan doc don’t appear to have the same characteristics. He has the frequency shift (velocity) over a relatively short timeframe without the powerful ‘burst’ in the middle*. However, having spent years in a past life, peering at spectrum analyser displays of different types of radar signals I do know that the settings of the equipment can present a display that doesn't necessarily represent what you are looking for. Your setup and Dr Morgan’s could be looking at the same event and have different presentations. (* I’ve just realised Dr Morgans velocity display effectively ‘folds’ the inbound and outbound frequency shifts and combines them into one value of velocity)

When you say "pulses" I think you mean dwells. As you know Graves is a CW radar and the scan dwells for 3.2secs at a particular azimuth angle. A 45deg scan taking 19.2secs to complete. You could well miss a lot of events while it was dwelling on another sector.

As I say this is all academic for me as I can’t see the signals down here to be able to get some kit and join in the fun.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Neil Wyatt on 21/06/2018 21:19:03:

Posted by Doubletop on 20/06/2018 21:39:23:

…

The ISS return also has those faint spectral lines how are they explained? There are also the lines at 143,046,800 143,048,900 and 143,052,900 something in the receiver?

…

The vertical lines are probably radar transmitters, that at 143,048,900 is probably the back signal from Graves itself, allowing for a small error in receiver calibration, the others being ATC?

The faint lines are probably receiver artefacts. SDR produces them if something in the receive chain is slightly out of balance. Even if the SDR module is properly adjusted not all computer sound-cards are wonderful. Also, being broadband, SDR can be overloaded – the lines may be the effect of a strong out-of-band signal.

Or they might be interference from nearby domestic, comms or industrial equipment. Even more likely because it's so close, the computer. If it matters enough to check, the strength of an actual signal varies when the aerial is swung, artefacts stay constant. Probably not radar or Air Traffic Control – no modulation.

Left my receiver running all day and noticed 4 or 5 echos. All small, the first event in the morning being by far the biggest. Microsoft doing a major update lost me a couple of hours. Bet that never happens to Jodrell Bank!

Dave

[SillyOldDufferModerator @sillyoldduffer]

Posted by Doubletop on 21/06/2018 22:29:31:

Posted by Neil Wyatt on 21/06/2018 21:19:03:

…

…

As I say this is all academic for me as I can’t see the signals down here to be able to get some kit and join in the fun.

Any FM Broadcast transmitters at a suitable distance from you? Before Graves helpfully provided a clean signal in a quiet part of the spectrum, people did similar detections with distant FM transmissions. The hard part was finding one that wasn't blotted out by local broadcasters using the same frequency.

[John HaineParticipant @johnhaine32865]

Assuming the spectrum is ~145 MHz, surely not ATC radar? I think they are all up at microwave.

Going back to my earlier observation, are there no signs of reflections off aircraft? Or are they flying too low for the range to the Graves radar?

[SillyOldDufferModerator @sillyoldduffer]

Posted by John Haine on 22/06/2018 07:20:53:

…

Going back to my earlier observation, are there no signs of reflections off aircraft? Or are they flying too low for the range to the Graves radar?

My maths is poor but assuming Dijon to be about 1100km away from me:

1. For both sides to see an aircraft mid-way the effective horizon distance is 550km (ie the aircraft has both sides in view.
2. From this calculator the effective height needed to get a horizon distance of 550km is about 25km
3. The ceiling of a Boeing 747 is about 13km

The closer you get to Graves the more likely you are to see aircraft. But from this distance from the ground station we can only see things more than about 25km high.

Last night the moon might have been detectable, but the distances require a better antenna than mine:

Yes that is a dustbin, old drain-pipe and second-hand plumbing. The rotary drier isn't part of the installation

Dave

[Neil WyattModerator @neilwyatt]

Posted by John Haine on 22/06/2018 07:20:53:

Assuming the spectrum is ~145 MHz, surely not ATC radar? I think they are all up at microwave.

Going back to my earlier observation, are there no signs of reflections off aircraft? Or are they flying too low for the range to the Graves radar?

Apparently they show as traces with small, constant doppler shift, but are mostly too low to be detected.

Meteors are roughly 4-5 times as high up as airliners.

[Neil WyattModerator @neilwyatt]

Posted by SillyOldDuffer on 22/06/2018 13:14:10:

The rotary drier isn't part of the installation

But it looks more impressive

http://www.britastro.org/radio/projects/Antennas_for_meteor_radar.pdf

Edited By Neil Wyatt on 22/06/2018 17:02:12

[SamsarandaParticipant @samsaranda]

Dave,

you say that you should only see objects above 25km but do temperature layers in the atmosphere play any part in what could be visible below that 25 Kms. I ask because back in the 60’s when stationed in what was Trucial Oman, on guard duty at night out on the airfield in the desert, we could listen to Radio Caroline but only for about an hour or two before dawn because the atmospheric temperatures created conditions for the signal from Caroline to skip the 4,000 miles or so.

Dave W

[SillyOldDufferModerator @sillyoldduffer]

Posted by Samsaranda on 22/06/2018 17:39:58:

Dave,

you say that you should only see objects above 25km but do temperature layers in the atmosphere play any part in what could be visible below that 25 Kms. I ask because back in the 60’s when stationed in what was Trucial Oman, on guard duty at night out on the airfield in the desert, we could listen to Radio Caroline but only for about an hour or two before dawn because the atmospheric temperatures created conditions for the signal from Caroline to skip the 4,000 miles or so.

Dave W

Yes, there are several things that alter the range of radio signals, some common, others exotic. The Graves Radar transmits VHF which mostly goes in straight lines. Normally most of the signal disappears into outer space rather than following the curvature of the earth, but there are conditions in which the atmosphere can reflect round the curve possibly getting bounced several times. I believe the distance record for communication in the nearby 144MHz amateur band is about 6000 miles, but that's very unusual.

Short Wave transmissions bounce very easily off the ionosphere, sometimes going all the way round and back. Medium Wave signals tend to behave like VHF during the day but they too bounce long distances as ionisation drops overnight, which is how you could hear Caroline. It's remarkably complicated and 'Quite Interesting' : listening to radio playing odd tricks is a full time hobby in itself.

Dave

 

 

Edited By SillyOldDuffer on 22/06/2018 18:50:08

[Neil WyattModerator @neilwyatt]

I read (and promptly forgot most of) the entry for 2m band on Wikipedia which explains/links to several long distance modes. I say explains but I think a few are still a bit of a mystery.

Some are so short and flaky they can only be used to send bursts of CW morse code that are so fast they have to be decoded by computer.

Neil

[MuzzerParticipant @muzzer]

Neil – why can't your pics be clicked on to open them? I've noticed this before – some pics can be, some can't, including the "For Sale" pics. On this page, SOD's pics can be clicked but none of yours can. Somewhat puzzling – and annoying.

Murray

[Neil WyattModerator @neilwyatt]

Posted by John Haine on 22/06/2018 07:20:53:

Assuming the spectrum is ~145 MHz, surely not ATC radar? I think they are all up at microwave.

Going back to my earlier observation, are there no signs of reflections off aircraft? Or are they flying too low for the range to the Graves radar?

I just found a test report ona radar using taht ferquency – but it seems it is used for 'stealth defeating' military radar.

Neil

[Neil WyattModerator @neilwyatt]

Posted by Muzzer on 22/06/2018 21:59:55:

Neil – why can't your pics be clicked on to open them? I've noticed this before – some pics can be, some can't, including the "For Sale" pics. On this page, SOD's pics can be clicked but none of yours can. Somewhat puzzling – and annoying.

Murray

Because to save clogging the net I've just linked to images I've uploaded on another site. Use right click 'view image'.

Here are some recent ones in a different programme that I've managed to persuade to log meteors and cature images of the bigger ones.

Time and frequency have swapped axes, but they each show one or both of the doppler shifted 'meteor head' and the static ionisation trail. The first one lasts around12 seconds.

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