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Posted (edited)

Hi there. New to this board. This looks like a good place to hang out and talk about SDRs as applied to meteor echoes and more. I've been experimenting with SDRs for months now as they combine some of my current and past hobbies, radios (shortwave listening), computers, and electronic gadgets. I started using SDRs for shortwave listening (whatever's left of that) and quickly found myself interested in other parts of the RF world, meteor scatter echoes being the low hanging fruit. One of my goals has been to set up a highly reliable system of logging/snapshotting (hehe … I like to make up words) meteor echoes, and I'm getting close. As we currently are under meteor crossfire (Southern Delta Aquariids, Alpha Capricornids, and Perseids) this has been a great time to tweak my setups and test for reliability. Also created a live meteor echo feed via YouTube for friends and anyone else interested in listening to hiss with an occasional meteor echo streaming across. I'm using an RSP1A via SDRSharp and recording with ARGO, HROFFT, and Spectrum Labs. Another setup I just started is an RTL-SDR and Echoes, with them being what they are behaving a bit touchy. Anyway, I've been gathering some interesting captures. Hope its not too many, don't wanna spam.

 

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Edited by Werner Roland
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Wow those are really nice echos! It would be so cool to map their directions, your "pings" seem to have far higher resolution than most. Its fascinating the way that they seem to split up on different frequencies. :)

John

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I Agree with John, nice shots.  I note you are in the US.  Could you please let us know some details of the Transmitter and software you are using for the nice spectrograms.

 

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Thanks Nebula. The software I'm using is SDRSharp (Build 1361), piping audio into Spectrum Lab, Argo, and HROFFT.  The transmitter is one of the few analog TV stations remaining (Sault Ste. Maries, Ontario, Canada, Channel 2,  55.24 MHz ) with a powerful enough signal and the right distance (800 km) from my location (Minneapolis, Minnesota) to work for meteor scatter detection.  Antenna is a simple dipole around 20 meters end to end, running north-south, with the transmitter ENE relative to my location.

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12 hours ago, JohnSadlerAstro said:

Wow those are really nice echos! It would be so cool to map their directions, your "pings" seem to have far higher resolution than most. Its fascinating the way that they seem to split up on different frequencies. :)

John

Thanks John. I'm still relatively new to this and I am trying to learn/understand the physical processes behind the various echo types.

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I think the relatively low frequency of the TX (55MHz) explains a lot to me about the nature of you spectrograms.  Nevertheless, nice captures.

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41 minutes ago, Geminids said:

I think the relatively low frequency of the TX (55MHz) explains a lot to me about the nature of you spectrograms.  Nevertheless, nice captures.

Could you elaborate? Thanks

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If receiving a TV transmitter, you'll also have modulation on the signal too.  Even though the TV signals are amplitude modulated, I suspect when viewed on the waterfall plot you'll be something similar to the charts presented in both time and frequency domains.

However, 55Mhz scatters better than 143MHz, so is likely that you'll also be seeing more effects from some of the rather strange bifurcations that can occur.  I've seen such effects from the 143MHz carrier wave transmitter of the GRAVES Radar in France and have only come across one paper describing them.  If I recall, the author was hypothesising that the cause is due to high altitude wind shear.

They are difficult to find in my data, so this example is by far not the best, but gives an example of the bifurcation that you may be seeing.  

event20190401_021117_32.jpg.6443f2ba5b09da5feb989dfd9f1f73b2.jpg

 

Richard

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Thanks Richard. I'll do some digging on this, sounds interesting. Just a quick question: This bifurcation is a physical aspect of the meteor ionization trail (such as wind shear as you said), not some anomality introduced by the spectral analysis, correct?

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Posted (edited)

That is a very good question, which I cannot answer with certainty, but I think there is a real world effect.

It's possible that some of the effects seen could be artefacts of the FFT.  Also, some of the bifurcation may be frequency scattering.  However from the traces I've seen there are a number that I cannot explain.  Here's a better one:event20190801_020255_136.jpg.b69c5ef8026bedb4a0bc62841982165a.jpg

I've seen traces wher bifurcated returns appear from nowhere after the start of an echo, or extend on after the "primary" carrier frequency echo drops into the noise.

GRAVES trasnmits a carrier wave, so the scatter returns should closely approximate to a carrier wave, such as this one:

event20190801_025852_235.jpg.9d4b4fd77108bacaa82ebcdeb197073c.jpg

The vertical "ticks" on the second traces correlate to and are assumed to be artefacts of the 2-second azimuth switching of the GRAVES radar.  The wideband noise occurs at the switching points and may be further artefacts of the FFT, or saturation of the SDR.  I don't recall seeing many of these artefacts on bifurcated returns.

I do have even better examples of bifurcation which clearly shows two or even three traces in the time domain.  If I can find them, I'll post.

My guess on your superb echoes, is that that they represent the modulation of the TV signal, possibly coupled with some bifurcation too.

Richard

 

Edited by BiggarDigger

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Thanks for the explanation. Gives me good food for thought. On the saturation, I see that quite often with very strong echoes. I've assumed it's overloading of the audio input of the sound card. That's the main reason I'm zooming in on the Spectrum Lab waterfall, so I don't get the "sidebands." With ARGO don't have a choice (to zoom in.)

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