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Old 21-10-2014, 03:07 PM
algwat (Alan)
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Radio Meteor listening

Gidday All,

I am trying to find a good frequency for listening for Meteor returns, here in west of Melbourne. Using an RTL-SDR I have found an interesting frequency a around 49.337Mhz.

does any one know this frequency?

I am listing in CW mode using HDSDR, It seems too have some interesting variations to the signal ... any info much appreciated.

kind regards, Alan
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Old 21-10-2014, 06:24 PM
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mswhin63 (Malcolm)
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Currently Meteor listening is done predominately through reflection at a frequency of around 140MHz but can be a range generally in the quite zone.

Usually transmitter approx 2000 K's away bounce off the meteor and reflect to your receiver.

There is a bit of info here - http://www.radio-electronics.com/inf...s-tutorial.php
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Old 21-10-2014, 06:58 PM
algwat (Alan)
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Thank you Malcom,
I am just a listener not a transmitter, and am trying to use small SDR's
This frequency seemed have some short burst signal level changes, and longer changes as aircraft moved by. Although it faded out as the sun went down? I managed to record a couple of audio wav's of the short events.

I have tried to listen for reflections at 140Mhz with WSJT9, no luck as yet.

kind regards, Alan.
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Old 21-10-2014, 10:57 PM
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Quote:
Originally Posted by algwat View Post
Thank you Malcom,
I am just a listener not a transmitter, and am trying to use small SDR's
This frequency seemed have some short burst signal level changes, and longer changes as aircraft moved by. Although it faded out as the sun went down? I managed to record a couple of audio wav's of the short events.

I have tried to listen for reflections at 140Mhz with WSJT9, no luck as yet.

kind regards, Alan.
Unfortunately it is a precision measurement tool, There is only a small window of measurement available, the higher the angle of reflection the smaller to coverage, hence 2 - 3000 km is optimal, too low creates other problems. The only other problem maybe the SDR if it is a $20.00 RTL2823U version has a noise floor at -60dbm which makes only strong reflections to make the grade. Most quality RF receivers run down to -120 to -150dbm which is quite a substantial difference. Still may display larger meteors though.
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Old 22-10-2014, 12:03 AM
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mswhin63 (Malcolm)
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As far as 49.337Mhz, nothing specific to that frequency although if it was man made it would be a bit different. The range 49-50MHz is designed for broadcast but unknown who would be using it. Possibly HAM broadcast.

Another possibility is a small amount of solar radiation, not likely but remotely possible.

You can get an idea of what frequencies to use or know about from this chart - http://www.acma.gov.au/~/media/Spect...2013%20pdf.pdf
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Old 23-10-2014, 07:08 AM
algwat (Alan)
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Thanks Malcom,

I got a couple of the noolec RTL T820 little green receivers and put them at the end of 5m powered usb extension cables, see image attached.
They work very good with HDSR and RTL1090 ADS-b software, see and hear lots of aircraft message

http://www.nooelec.com/store/sdr/sdr...832-r820t.html

The attached images are of my portable (small)equipment.
The noise levels a around 110db.
The image with the air traffic shows a short burst level change, not from the air traffic. I am suspecting a meteor but not yet proven.

Also , seeing these converging and diverging signals when out side, some short and long cross overs.


Would be interested to hear if others can get these variations from better equipmnet.
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Last edited by algwat; 23-10-2014 at 08:37 AM. Reason: add images
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Old 23-10-2014, 10:30 AM
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I don't have time to test the receivers as I also have the same receivers. I did not get -110dbm out of them though when I initially set it up. I also used the same software as well.

I did not have a lot of time to play around with them, so I will when I complete this years Uni.

The cross over or what appears to be Doppler shifted signal maybe a good signature for something moving. I cant shed any more light on that apart from that it looks good for investigating.

One thing I am not sure of as yet, but I want to find out whether the Ionisation of the meteor produces it on signal based on the energy that is dissipated on entry. I haven't found anything that would suggest that and not sure where to start on that one. If it does emit a frequency where is it on the spectrum!!??

For me it is an interesting field and would really like more time to work on it as well. Maybe one day. I have in mind and alternative radar system that may or may not work. I hope that one day I will work on it. Holidays coming but a lot of project s to complete.
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Old 23-10-2014, 05:26 PM
algwat (Alan)
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Gidday Malcolm,

I am sure that I am seeing local aircraft in at a training airport near by.
This is what the converging signal is catching. Still not sure of the source but I have found a couple more around 49Mhz that show similar events. I have a suspicion about the source ,so still looking

You might like this interesting link, http://livemeteors.com/

kind regards, Alan.
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Old 23-10-2014, 09:46 PM
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Thanks for the link, TV transmitters are the most popular, although US still use analogue TV signal. Surprisingly backward on digital TV.

One thing I suspected is the frequency used is 13KHz off frequency, There is a fair amount of drift on the SDR Dongles. The drift though can be offset to compensate for drift. 55.25MHz is the channel 2's TV channel frequency, which is being picked up.

Not a major problem though as you still need an offset to detect the meteors.

Suggest you try to tune into an number of TV Station channels that cannot be received in your area.

While typing this message I left the livemeteor running and heard so many strikes. Must be picking up loads of minute strikes with so many picked up.
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Old 25-10-2014, 05:19 PM
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There's no analogue TV left in Australia is there? I used to pick them up on Ch 0 - 2 when they were active.

https://www.youtube.com/watch?v=06GMm_EoLkY

What about FM stations? Are there any clear spots on the FM band in Vic or is the band full now days? I hear pings from Sydney FM here when doing FM DX but I live in a regional area so don't have as many FM stations.
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Old 25-10-2014, 05:32 PM
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The principle of Meteor burst detection is only to pick up a reflection of a signal from the ionisation of the meteor trail. So any transmission should work theoretically. Even digital signals may bounce off the ionisation trail and reflect towards your receiver. The reception signal though may appear to be different though, I am really not sure what it would sound like. Most signals should work, but I read somewhere that around 140MHz is the optimal frequency but I suppose any frequency will work but may have some limitations.
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Old 25-10-2014, 07:46 PM
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The problem with digital is that it needs a hell of a good signal to get a good BER and it's wide band. You're better off with narrow band signals which makes FM a better choice, or if you have a good yagi try for amateur radio beacons on 144 MHz. I used to get pings from VK4RTT about 800km away on good mornings with a 12 el yagi. I'm a bit out of date but a lot of the Ham guys used to do whisper or similar every morning also via meteor scatter.
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Old 26-10-2014, 12:40 AM
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If you wish to receive the digital signal, you can still receive as a CW signal as you will only get garbled noise at a higher signal level. The idea of signal detection is not to de-modulate but to receive an indication that the carrier or modulated data is being received. So BER is not the going to be a problem in this instance.

I think though the transmitter power is lower than the previous analog station so it is likely the reception will be weaker. I have been trying to source transmitter power levels but bit hard to find.

I think the best alternative is to simple listen out on a frequency and see if you can get anything back, trying 1 station at a time. If you are considering a specific antenna design then I suppose it maybe best to find a carrier transmitting somewhere and design the antenna to that. Still not sure if the reception will be received even about the antenna is built. I do recall Ham radio transmitter beacons but I think they are few and far between. Mostly Northern hemisphere.
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Old 30-10-2014, 01:42 PM
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Quite a few beacons on the 2m (144MHz) band around Australia, but they are mostly low power. High gain directional antennas, mast head amps and narrow band receivers can make up for that.
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Old 01-11-2014, 04:51 PM
algwat (Alan)
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I think the 49Mhz signal I was listing to may have something to do with the mobile network, I found a few of the oscillating signals near me around this band.

So, kept looking at lower frequencies, this one at 23.381 Mhz has interesting activities. Some very short at occasional long. Still not able to determine the source.

kind regards, Alan.
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Old 05-11-2014, 09:17 AM
algwat (Alan)
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Ok, so this 23.381 Mhz signal in FM is some one talking and playing music. I heard Colac? mentioned. That's 100Nm west from me in Melbourne. I can only get it when the suns setting.

In CW mode the signal is not strong and mostly not there. Then occasional very short higher power squeals. When a big one happens I get three carriers the centre being strongest. other wise just a good long squeal.

I would be interested to hear if others can get this from Melbourne?
or, with better equipment from further a field?

regards, Alan.
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