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Goldchip

Meteor detection

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Hi all,
Here in sEast Sussex I'v spent some time now trying to set up a meteor scatter receiver using the Graves Radar site in France, but so far without sucess.

My set up is as follows;
5 element diamond yagi (2M ham band) about 5M above ground level (on roof of bungalow)
30-35 Metres of RG6 coax
My home made Bias tee (Adams design)
RTL SDR
SDR# software.

I can receive fm stations and ham conversations in the 2m band, but dont receive anything when tuned to the Graves frequency of 143.049Mhz.

The yagi is horizontal, would mounting it verticaly be worth a try?

Others seem to make it look very easy, Any help would be appreciated.

Thanks.

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I wonder what you're using the bias tee for ? .. normally they are for sending power up the coax to a mast head pre-amplifier.

Where do you have your yagi pointing, and does it have a clear view of the horizon and sky in that direction ?

Your 100'ish foot of RG-6 coax will have around 2dB loss, plus maybe a couple more for connectors and impedence mismatch (your yagi will be 50R and not 75R for one), which is managable. It maybe that a good low-noise mast head pre-amp is in need.

If not meteors, you should give the odd reflection from satellites, although the doppler shift for low earth orbit satellites at around 143MHz will be up to around 3.5kHz when they are close to the horizon.

Edited by Pippy

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Thanks for your reply, I'm new to all this.

I considered using the RTL SDR to power the coax, but I didn't fancy modifying and possibly messing up the RTL circuit board.

I hope to also need the bias tee to power future additions..........I'm currently constructing a 3m dish for observing the 21cm hydrogen line emissions.

The yagi is manually aimed south east towards Graves, so it could be a few degrees out, I have tried adjusting it many times.

Yes I agree the 100' RG6 together with the connectors and mismatches etc is not ideal, but the LNA is next to the yagi and I would have expected to see at least a feint echo from something, as you say.

Also, the yagi was originally only 50' away but I moved it because I was running out of things to try, the noise floor and reception seems to be the same.

Any thought on vertical polarization?

 

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1 hour ago, Goldchip said:

Any thought on vertical polarization?

You have an LNA at the antenna :) .. you didn't mention that in your original post so thought it best to ask. Wonderful !

I think graves transmits using circular polarization (not sure if it's right hand or left hand), which normally means it won't really matter what the polarization of your reception antenna is (assuming your antenna is linear polarization - vertical, horizontal or slanted).

How the reflections arrive back at your antenna is another matter though, but in general, being as your yagi is linearly polarized (ie not circular), it shouldn't really matter how you orientate your yagi. So just go with what you've got.

I know their are others on the forum who are receiving graves (I currently don't), so hopefully they might pipe up and help you more than I currently can.

 

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I'm getting reflections from Graves up here in County Durham but found that two things made a difference as at first like you I wasn't getting anything at all at 143.049. 

I. My rtl sdr dongle displayed frequency wasn't accurate. I needed to set it at 143.048 displayed to get 143.049 actual. Your offset may be different. It also alters with temperature. There's a vhf beacon near maidstone which transmits at 143.430 which you might be able to use to calibrate your frequency if you can get line of sight. Look up gb3vhf on google. 

2. I got better results with my yagi oriented horizontally and pointed at 115' from my location which is somewhat east of the Graves bearing from me.

So It might be worth experimenting with different frequency offsets and different antenna bearings.

Cheers

David

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That's encouraging, If Graves can be received in County Durham I'm sure I will succeed eventually! 

I have learnt quite a bit about the dongle frequency stability, and regularly use the weak but readable gb3vhf ham vhf beacon you suggested to keep check on the frequency offset, mine is adjusted by 45ppm.

The dongle is "always on" to try and keep the temperature stable. 

I thought mounting the Yagi horizontally would probably be best so I will leave it at that, but I'll play more with the direction, pointing east of Graves is interesting.

Thanks.

K.

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Thanks Pippy, I forgot to mention the LNA.

I also should have mentioned I'm only 2 miles from our local tv mast and get swamped by VHF radio broadcasts, I'm waiting delivery of an FM blocking filter which I hope will help.

K.

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Hi Goldchip, just a few pointers to consider.

The direction of the antenna is not critical but as a start centre on Graves. With a 5-el Yagi I guess that the beam width will be reasonably narrow, but even so meteor scatter signals are produced over quite a wide area of sky, as Graves transmits towards the South, as I've identified in this map from my own location. The transmission is between 15° and 40° in altitude, and the shaded area represents where scattering can take place at ~100km altitude. You do need a clear view to low on the horizon, ideally.

Graves transmitter zones.jpg

Don't worry about polarization, folk use both vertical and horizontal orientation with equal success it seems.

Don't forget that you won't normally detect the Graves signal unless there is a reflection from a meteor or the ISS for example.

I test my set-up by tuning to the VHF beacon GB3VHF, which transmits precisely on 144.430 MHz. See http://www.gb3vhf.co.uk/ . He transmits from Kent using two antennae, as is shown in this map:

GB3VHF%20beacon%20288%20&%20348%20beam%2

 

I use this to set my off-set.

Even accounting for your losses I would have though that with a 5-el external antenna, and living in the SE of the country, you should get plenty of signal. I use a 3-element LFE-Q quad in my roof space and do fine.

There's plenty off stuff on this thread to set you up, though I know that there are a lot of pages!

Come back with any questions.

Cheers, Ian

Edited by The Admiral

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Thanks Ian, I think I will raise the Yagi a little, and start working through that thread.........

K.

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Hi Goldchip,

Sorry to hear you have not been able to detect any meteors with your set up. While I cannot help you in any technical way (and I use use the FunCUBE pro+ dongle, Spectrum Labs (SL) software and home made S@N antennae and not your set up) you really ought to be picking up the reflected GRAVES signal from some meteors even if there is little shower activity currently and perhaps low sporadic numbers. With SL using the correct script is most important to detection, I don't know if this is relevant to your set up? Your equipment is obviously otherwise operational to pick up other signals. Your best time to detect more reflected signals would be in the early morning hours to dawn and fewest around 8 PM. You may have been very unlucky and the Graves site was down for maintenance when you tried before. It is a moot point where your antenna should be pointed as the area where reflected signals can come from is quite wide and affected by the altitude of the object (I once followed the ISS from a point south west of Ireland to just off the west coast of Italy near Rome). I have the antenna pointed at the GRAVES transmission site with a 10 degree incline. The antenna is horizontally polarised and it has a clear line of sight to the SE over the Trent Valley and beyond which I feel helps.

I hope the read of the link proves helpful.

Cheers,
Steve

Edited by SteveNickolls

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Hi Goldchip. I don't know what you are expecting to see, and why you think that you are not receiving meteor scatters from Graves. They are not frequent outside of shower activity, and sitting in front of your screen for many minutes on end waiting for a strike can be frustrating. I started off with SDR Console, rather than SDR#, but they do much the same, but in the end frustration got to me and like many others migrated to Spectrum Lab for its ability to record the strikes. Personally, I'd stick with what you have until you can be sure that you are picking up traces. Adding complication before that could compound the problem.

I'm not sure how much the vhf interference is affecting your success, but I'd have thought that if you are receiving GB3VHF it should be OK.

Good luck.

Ian

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115' from me is east of the Graves bearing but I have a much lower horizon in that direction. Directly at Graves I have a fairly sizeable ridge in the way. 

The pickup beam on my Yagi is about 60' so essentially I'm looking at approx 85' to 145'. 

I do get fewer hits than those in the South of England but I do get them. 

2.00 am to about 8.00 am seems the best time for me. 

I agree Spectrum lab is the way to go. Sitting listening for pings is soul destroying. 

Good luck.

David

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