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Coto

Meteor detection from Greece?

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Hi all,

 

I’ve been interested in meteor detection, but the problem is the GRAVES radar is too far from me (I live in Greece). I haven’t done any proper attempts, but is it possible for me to do meteor detection given my location? Does anyone know of a VHF radar transmitter near me? If there’s none, is it possible for me to get build a transmitter just for myself, or is that too impractical?

 

Thanks!

 

EDIT: Apparently it’s also possible with FM radio stations acting as the radar transmitters. My question is, you’re obviously tuning to a frequency between stations to avoid directly listening to the stations themselves, but why do the reflections off the ionized meteor trail not end up at the same transmitter frequency?

Edited by Coto

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There is certainly the possibility of receiving signals from GRAVES in Greece.  However, there may be real world limitations that make it very difficult. 

Many years ago, I ran a system of 4 stacked and bayed yagi antennae on the 144Mhz amateur band.  The array was as large as domestic garage mounted on top of a lattice tower.  Not something the average meteor observer might be interested in.  I was successful in many long distance contacts up to and exceeding 2000km on both meteor scatter and Sporadic E propagation, plus successful moonbounce contacts too.  On occasion I made contact with radio amateurs in Greece from central England by 144MHz Sporadic E, so it can be done.

Using forward scatter, the maximum range for meteor scatter is around 2200km.  If both the transmitter and receiving stations are illuminating the sky on their horizon such a distance is achievable.  However there is the likelihood that the main lobe from the GRAVES radar is elevated by several degrees, moving the common volume towards the transmitter site.  Also, in order to receive signals at these ranges, high gain antennae and low noise receiver systems are required.  At these frequencies, low noise can be achieved reasonably easily, but high gain antennae are, as noted, very large and cumbersome.

You can use a more local VHF FM transmitter, but it needs to be out of groundwave range, say at least 300-400km distant and return scattered signals may be swamped by local stations operating close to the distant transmitter frequency

In is possible to build a meteor radar system yourself, but there are again practical issues to consider.  You would need a radio licence (probably a radio amateur licence would suffice).  You could setup a distant transmitter, remote controlled over the internet and listen for scattered echoes at the receiving station.  Don't underestimate the transmit power and antenna gains required though.  A time multiplexed radar with 100% modulated carried where you listen for echoes in the gaps between transmission such as in primary radar systems would result in very significant sideband noise, be very unwelcome to any other spectrum users nearby and likely be shut down by the authorities quite quickly, so a remote transmitter is really the only option.  Even then leaving a strong carrier radiating on an amateur band 24/7 is also likely to be unwelcome.

The cost of suitable receivers and a modest antenna is not great and there are a couple of very prolific showers coming up over the next couple of months.  I would be tempted to erect an antenna, say a 15 element yagi, fixed at your horizon pointing at GRAVES.  Equip it with a low noise mast head pre-amplifier, very low loss co-ax feed plus suitable receiver and see what you get from the Geminids shower in December.

Richard

Edited by BiggarDigger
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Thanks a lot Richard!

Could you give me some tips as to how I could go around the FM station method? Other than looking for a quiet frequency, what else should I be looking for? Should I be looking for stations outside the country/in the 300 km+ range, and trying to tune to their frequencies, or would I (statistically) nearly always get lucky on every quiet frequency?

I'm using a simple λ/2 dipole antenna I quickly built, pointing to zenith. Should I be pointing to a lower elevation towards the horizon, and in what direction?

Thanks again

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A quick reply before work. I'll try add more detail later if I can.

For the FM transmitter route, try to find a station at least 300km distant (ideally more).  From a meteor scatter perspective, it doesn't matter which direction the station is, but if it is behind mountains signals will be reduced and if in the direction of a large nearby city a lot of noise will be present.  You should look for a transmitter with no other stations on the same frequency nearby which will mask the return echoes.  I should think there should be lists of stations, frequencies and locations somewhere on the web.

For this geometry, you would need to point the antenna in the direction of the transmitter or close to it.

I imagine you would need a lot more gain on the antenna too, but the advantage of the FM transmitter is that they are often radiating high power reducing the gain required at the receiver.

Richard

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A quick look on the web this evening finds this resource http://radiomap.eu/ which may help identify suitable VHF FM stations.

However, I recall now that there was some discussion a few months ago in this forum about using aircraft navigation beacons as the transmitter source.  These might be a better option if only because its unlikely that there would be interference from a transmitter local to the receiver.  It's also likely that a aircraft navigation beacon radiation pattern would be better suited than that of FM radio transmitters too.

Whichever route is taken, elevation of the antenna may be necessary to illuminate a common volume at approximately 90km.   A bit of simple arithmetic should give you an estimate of the ideal angle, but I wouldn't loose too much sleep over the accuracy because the 3dB beamwidth will be quite wide, so an approximation should be good enough.

Good luck!

Richard 

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So how's your effort coming along Coto? I started with sloppily arranged dipole to ferret out available RF sources feeding an RTL-SDR (which is a great starter choice, just be aware of it's sometimes crappy USB connection) and now run a 6m 3 element YAGI feeding several SDRPlays with great success. Small steps.

Werner

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On 16/11/2019 at 03:15, Werner Roland said:

So how's your effort coming along Coto? I started with sloppily arranged dipole to ferret out available RF sources feeding an RTL-SDR (which is a great starter choice, just be aware of it's sometimes crappy USB connection) and now run a 6m 3 element YAGI feeding several SDRPlays with great success. Small steps.

Werner

I tried with a dipole with no luck. I could see FM stations fine, direction was OK too, I think. I haven't given it another chance since, mostly because I'm working on other things like PICTOR (https://pictortelescope.com/ - https://github.com/0xCoto/PICTOR), but I wish to try again soon. I've got an LNA, maybe that can help instead of building a directional antenna (e.g. yagi).

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6 hours ago, Coto said:

I tried with a dipole with no luck. I could see FM stations fine, direction was OK too, I think. I haven't given it another chance since, mostly because I'm working on other things like PICTOR (https://pictortelescope.com/ - https://github.com/0xCoto/PICTOR), but I wish to try again soon. I've got an LNA, maybe that can help instead of building a directional antenna (e.g. yagi).

The LNA will help, but I suspect you'll also need a directional antenna if attempting this with the GRAVES Radar.  Since you'll be close to maximum range for meteor scatter, the signal will be very weak.  The LNA will help with that, but a directional antenna will reject local noise sources making detection much easier.  

FM radio stations are typically wideband to give better audio bandwidth and fidelity (greater modulation index).  Meteor reflections of such signals will be phase and frequency shifted and making automated detection rather more difficult I suspect.

This list of navigational beacons in Greece may give a different option:  http://worldaerodata.com/nav/Greece.php

With many beacons being only 10Mhz or so from FM radio stations, you may not need to adjust the hardware too much.

The Leonids shower peaks tonight, so is a guaranteed source or incoming meteors to test different configurations.

 

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