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furrysocks2

Meteor detection - is my kit suitable?

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I'm up in Fife and considering making a yagi and connecting to a receiver I've got - a wee experiment with my son and something to do. I've got a few questions, I wondered if anyone can help me.

I've got solid aluminium rod, I think 10mm but will check (I was making a table football table a while back and these are left over). I read I might have to adjust length and spacing, but result would be larger bandwidth. Any comment?

The receiver I have has AM, NFM and WFM - is it suitable? It will do the graves frequency, but can only detune in 5kHz increments - I'm assuming result will just be a higher pitch, but still within range of a sound card for processing?

 

Should I be able to get results, or is the above a non-starter and should I rethink?

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10 minutes ago, furrysocks2 said:

The receiver I have has AM, NFM and WFM - is it suitable?

My understanding is that you need Single Side Band (SSB) to detect the Graves transmitter but hopefully someone who is really into this will come along soon and advise you!

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35 minutes ago, steppenwolf said:

My understanding is that you need Single Side Band (SSB) to detect the Graves transmitter but hopefully someone who is really into this will come along soon and advise you!

Thanks - I'd read that. I think it's "half AM" or something, but I it's not something I understand.

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1 hour ago, furrysocks2 said:

I've got solid aluminium rod, I think 10mm but will check (I was making a table football table a while back and these are left over). I read I might have to adjust length and spacing, but result would be larger bandwidth. Any comment?

I'm not sure what you mean? What plan are you following for making the Yagi?

1 hour ago, furrysocks2 said:

The receiver I have has AM, NFM and WFM - is it suitable?

I don't think so. You need to be able to convert an unmodulated wave (the Graves scattered radiation) into audio, which means the receiver needs to supply it's own frequency. You can use Single Sideband (SSB) or continuous wave (CW), not frequency modulation (FM). Generally, the bandwidth for CW is set quite small, and isn't ideal for detection of what is a rapidly changing frequency wave followed by a fairly constant frequency wave.

Ian

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Adding further to Ian's has post above, a transmitted SSB signal has, not only one sideband removed, but also the carrier.  To be able to demodulate (hear the audio in this case), you need to re-inject a carrier wave.  In an SSB receiver, this is done by injecting a Beat Frequency Oscillator (BFO). 

Here's an article that explains a little about SSB  https://www.electronics-notes.com/articles/radio/modulation/single-sideband-ssb-basics.php

An AM receiver does not have a BFO and, without that, an AM receiver will not, as Ian noted, be able to resolve or demodulate the carrier waver from the GRAVES radar.  In theory,  a narrow band FM receiver will produce DC impulse directly from the FM demodulator caused by the initial Doppler Shift.  However, in reality this will be difficult to extract as it is applied to the audio stages by capacitve coupling to filter out DC impulses.  You may hear clicks from a narrow band FM receiver, but these will not be of much use the downstream signal processing.

An alternative, and one that is not at all expensive is to use a Software Defined Radio (SDR).  Most contributors here use these devices and they range in price from around £20 to a little over £100 on eBay or elsewhere.  My own installation uses an RTL-SDR, which is limited in bandwidth and sensitivity, but is perfectly adequate for meteor detection.  Generally speaking the more expensive the SDR, the more bandwidth, sensitivity, software compatibility and features it has.  If you go down the route of an SDR, consider if you'll use it for other things in the future to make a judgement about cost/performance.

For the antenna, you don't need wideband (frequency), but may wish to consider the beamwidth and rear & side lobe suppression to reduce any interfering signals.  As discussed elsewhere in the forum, at our lattitude (I'm located near Biggar), we need to look as close as possible at the horizon to receive good reflections from GRAVES.  Those further south are able to elevate the antenna if necessary.

Richard

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51 minutes ago, furrysocks2 said:

I'm looking at two designs

A lot of people use the design given in the Sky@Night journal. Simple to make using readily available bits. Can't find a link to the pdf right now, but I think somewhere it's given in this thread .

Being a long way north you might want something with more elements, but give it a try first as you've nothing to lose and it's not difficult to make. For something more refined, I'm sure BiggarDigger with his radio background can provide further information.

One of the advantages of using the rather more expensive Funcube Dongle SDR is that it works directly on your PC out of the box, I think for the others it is a bit more involved and there are work-arounds.

Good luck. Ian

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1 hour ago, furrysocks2 said:

Thanks, both.

I'm looking at two designs in https://www.britastro.org/radio/projects/Antennas_for_meteor_radar.pdf, and also trying to find my antennae book.

Had the receiver sitting on the shelf and frequency range was ok. Shame. SDR was going to be the next option.

I used those plans, fig. 2.1, but used 6mm aluminium tube and the performance is excellent with a £16 SDR.

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Massive Meteor.jpg

Edited by Stub Mandrel
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