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BiggarDigger

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About BiggarDigger

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    Nebula

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  • Gender
    Male
  • Interests
    Astronomy (obviously!), IT (work - ugh), electronics and radio engineering, meteorology, fresh air and wide open spaces.
  • Location
    Biggar, Scotland
  1. That's pretty much the orbital track that I saw Ian. It was using an historical ISS tracker, but it placed the ISS just off the coast of the Basque Country in the Bay of Biscay heading South towards the Pyrenees. Perhaps there's a minor discrepancy in the timings. Nonetheless, both the Mediterranean and Biscay would be backscatter off the frontal lobes (or perhaps sidescatter in the Biscay case). I looked up a few passes in the coming weeks and noticed two interesting passes on Friday evening this week. I'm working from my phone, so don't have the detail to hand, but if I recall, there's a pass at a little after 8pm South of Graves and a second later in the evening North of Graves. I'm hoping to book some quiet time on Friday evening to watch the reflections and if I can capture both, it may give further information on the backfire radiation and hence antenna alignment. Watch this space!
  2. I didn't get time last night to review the documents and papers, but will try tonight to look through them. However, I did stumble across a Google site: https://sites.google.com/site/radioastronomydm/observations/meteors which describes my suspicion about forward scatter from rear lobes. If this is correct (and the geometry suggests so), then there are further implications for antenna arrangements. People located in the southern areas of the UK may be better served by having low frontal lobes and an antenna pointing close to the horizon in order to receive back scatter from the forward radiating lobes at the transmitter. People, like me, in the North of the UK would likewise be best served by antennas pointing at the horizon with low frontal lobes to be able to receive forward scatter from the rear lobes of the array. This will be sub-optimal as radiation from the rear lobes should be significantly lower than the frontal lobes of the transmitter, but there's not a lot we can do about than other than move South! The interesting area is in the central part of the UK (central England, Wales etc), plus most of the Republic of Ireland. The geometry suggests these locations may be better served by elevating the antenna to try pick up the forward scatter from reflections over the English Channel or Northern France. Low angle lobes and horizontal antennae would be looking for back scatter over Southern France or beyond, which may be at the maximum range for 100km height reflections. There should be a balance point somewhere depending on latitude, front lobe pattern and gain of the receiving antenna whether it would be better to go for rear lobe radiation or frontal lobe radiation from GRAVES. I looked up my detection of the ISS, which was at 09:25 on the 2nd September this year. Historical tracking puts the ISS over the Bay of Biscay at the time: This which would have been a back scatter from the frontal lobes at GRAVES, with a potential meteor off the rear lobes too (again ignore the heterdoyne fro my PC monitor). I'll see if I can find a suitable prediction for a pass over northern France or southern UK, detection of which would confirm radiation off the rear lobes. Richard
  3. Thanks both, those look very interesting references. I'll need to review them this evening after work. I still lean towards the majority of my meteor detections being due to forward scatter of a rear lobe from the array, if only due to the geometries involved. Very intrigued by a report of an ISS detection over Ireland. I've got a record at home of an ISS detection which I'll dig out later and see if I can correlate the date and time to a location. In my data, I see quite a few minor reflections with head "echoes" but yes, the stronger bursts can cause aliasing within the FFT algorithm, particularly when the GRAVES array switches antennae. However, these do tend to be noticeably different to the bland trace in my first screen shot. Good job the skies are cloudy tonight as I foresee an evening of reviewing papers and articles ahead! Richard
  4. I've been pondering a question about the path geometries from my site on the northern edge of the Southern Uplands of Scotland and the GRAVES transmitter site. I suspect I'm seeing a lot of non-meteoric detections and indeed a number of long period reflections from what I believe are high flying aircraft in addition to meteor trails, but this leads me to question the radiation patter on the GRAVES transmitter site. Some initial assumptions: GRAVES is radiating in an arc centred approximately in a southerly direction The transmitter antennae have a decent front to back ratio, and, The frontal lobes are elevated skywards, meaning the rear lobes are actually pointed in to the ground (all of which can be inferred by photos of the site: interestingly, Google Maps etc now have the area blurred, but there are plenty of photos of the site online) Based on these assumptions, it follows that the reflections we detect should be back scatter from incoming meteors over Southern France or beyond. The conundrum I've been pondering is that those locations in Southern France, Iberia, Italy and the Mediterranean are well out of my 100km height radio horizon, so I must be receiving forward scatter from signals radiated to the North from GRAVES. My 100km height radio horizon is just about into Northern France, so the reflecting medium is either much higher and I'm detecting meteors south of Graves, or I'm seeing forward scatter radiated in a Northerly direction. So something is amiss, either in my assumptions, or the heights of the incoming meteors that I detect. My suspicion is there is a significant rear lobe radiating from the site. The primary reason for this suspicion is that I see long period reflections of the order of 15 to 20 seconds (or more) which do not exhibit the typical Doppler shift and which are modest in strength. Placing a high flying jet liner over the Southern half of the UK at 12km altitude, gives a path which would see both GRAVES and my site, allowing for a little over the horizon tropospheric propogation. Such aircraft would, I think, be flying slow enough to give long period reflections and minimal Doppler shift. If there is a notable northerly radiation from the site, I may be lucky enough during periods of significant tropshperic enhancement to hear the groundwave from GRAVES. However, much more likely that sites in Southern England would hear it under such conditions. It would be very interesting to know if anyone has heard GRAVES on a direct ground wave in the UK. Here's a few examples: 1. what I believe are aircraft reflections and 2, what appear to be meteor reflections: 1. Aircraft? 2. Meteor (ignore the heterodyne around 1420Hz as this is caused by electrical noise from my PC monitor) Richard
  5. BiggarDigger

    Meteor Scatter Antenna Testing

    Easy mistake to make Ian! Glad you found the culprit! To pick up on a couple of earlier points, Yes, the gain bandwidth of a Yagi antenna tends to be narrow and generally gets more so, the more parasitic elements you add to the array. Eventually the array becomes so sensitive to external effects as to be unstable. Fewer elements usually mean broader usable bandwidth, less environmental sensitivity and broader frontal lobes. I'd be a little sceptical of the 12.5db gain figure calculated by the software for a 3 element array. A more realistic value might be in the range 5-7dBd. Even allowing for gain over an isotropic radiator adding an extra couple of dB over a dipole would make 7 to 9dBi. In any case however, since we are not interested in weak signal propogation and want reasonable broad horizontal forward lobes, a gain of around 7 to 9dB is perfectly acceptable. GB3VHF is an excellent source to check functionality, but directly comparing two antennae against each other using it would a bit hit and miss. Environmental effects and propogation effects will make much more difference than tuning or antenna gain unless (assuming like for like antennae). This makes a good case for the refelctometer described in the original post since, assuming the noise source is stable and antenna feeds are calibrated, means the absolute tuning points can be compared. Radio signals at 144Mhz can and do propogate over the radio horizon tropospherically and ionospherically. Indeed, the meteor refelections we detect are ionospheric propogation and the ground wave, beyond radio horizon, is tropospheric. Depending on local weather conditions tropospheric propogation can increase or decrease the received signal dramatically. It would not surprise me if over the coming couple of months, I am able to hear the GB3VHF beacon here in Southern Scotland even with a modest antenna when super-refraction occurs in the troposphere. Ionospheric propogation at 144Mhz comes in many forms: but for our purposes, we are interested in the plasma effect in the ionosphere of incoming meteors. One other item that I've been pondering for a little while is the path of signals from my receiver to meteor plasma trail and onwards to GRAVES. I'll start a new thread for that so as not to hijack this one! Richard
  6. BiggarDigger

    Meteor Scatter Antenna Testing

    That's right Ian, the VSWR of the yagi antenna should be fairly broadband (as the feed to the dipole would show). However, being a parasitic array, the forward gain achievable should be fairly narrowband; At least for a reasonable sized yagi array anyway. I'm not certain how many elements the Sky at Night array had, but is it were only 3 or 5, then the forward gain might be reasonably broadband. Some years ago I used multiple stacked and bayed 17 element antennas at 144Mhz and similarly, multiple 21 element antennas at 432MHz for EME (moonbounce) work and can be sure that the bandwidth of the forward gain of those monsters was pretty tight. Anyway, that's straying off topic: I think the idea of using an SDR with a directional couple and noise source is an excellent little project to tune the antenna, but as noted, there are equally good methods to get "close enough" for meteor logging. Cheers, Richard
  7. BiggarDigger

    Meteor Scatter Antenna Testing

    The homebrew reflectometer described in the RTL-SDR article is a really good application of SDR technology outwith the mainstream radio receiver application. It's useful for filter setup and can, as they note in the article, be sued to measure VSWR. However, VSWR isn't so important for receiving antennae. This is because there is no danger to any transmitter final stage amplifier as a result of poor matching of the feed or the antenna. Nonetheless, a very bad VSWR will yield poor results for your meteor detector, so ideally you want a decent impedance match between the antenna, feed and RF input stage of the SDR. A reasonable approximation can be obtained as The Admiral notes by tuning for decent performance on the GB3VHF beacon. It's some way off the GRAVES frequency, so if your antenna is narrowband, as most Yagi arrays are, you could be a little way off optimum though. I'm outside the groundwave range of GB3VHF, at least with a low-gain, low-height antenna anyway, so that route wasn't available to me. I used the wideband noise emanating from the Sun to tune the antenna. It doesn't matter that the Sun is high in the sky: your'e not looking at absolute noise levels, but tuning for the maximum noise achievable. Solar radiation at 144MHz is quite noticeable and can usually be discounted from other sources by the directional nature of the antenna. Yes, it took a bit of rotating the antenna to be sure of noise source and a bit more back and forth to the SDR and software, but I was able to adjust the tuning capacitor to maximise the wideband solar noise and hence centre the tuning of the antenna on GRAVES fairly easily. I use a so-called HB9CV antenna which is a two element active phased array, similar in performance to a 3 element parasitic array such as a Yagi.
  8. I use both the 9x50 straight and a Telrad, on a 2" riser base: The base is cable-tied to the OTA. This will allow me to remove it easily in the future without having to resort to acetone or similar to soften the sticky pads. In addition to the Telrad, I also use a Water But Stand with a plywood base, similar to the arrangement here: Using that, I no longer have to stoop to the eyepiece and makes it a lot easier on my back. Richard
  9. BiggarDigger

    First night with the new 8" 200P Skywatcher

    Nice report! The 200p dob yields an amazing bang for the buck. Sure, the mount could be improved, but by saving money on the mount you get optics well above what you might otherwise expect. It does what it does very well and I've had many a "wow" moment with my 200p. To help with viewing, I built a water-butt stand for mine. There's several threads in the forums here (I'm on a mobile device just now so less easy to search and find you a link). My stand includes 4 adjustable kitchen unit legs and a plywood shelf onto which the dob base fits. It raises the whole scope by 20 inches or so. I echo the comments about M31, but even if you're a little underwhelmed by it, bear in mind that you're looking at hundreds of billions of stars and the light entering your eyes started it's journey before the evolution of mankind. Good luck with seeking out many more wow moments. Clear skies, Richard
  10. BiggarDigger

    Cirrus or a Galaxy?

    Yes our skies are really good. According to Clear Outside, my estimated sky quality is 21.33. A couple of years ago the Council changed the street lighting in the village to LED, which made a tremendous difference, particularly away from the North. To be honest though, I haven't calibrated that number as it only takes a neighbour to turn on an outside light or the farmer to be out with a nightsun and I'm dancing around trying to find shadows. I tend to use feint and tenuous objects such as M1 or M33 through the stock 25mm eyepiece on the 200p as my "calibrator" for what I might observe on any given night. I've definitely seen several brighter patches in M33 through the eyepiece. On the best nights, the central part appears to be slightly mottled and the outer structure has brighter blobs of fuzziness. I can't say for sure if anyone of those is NGC604 or any other active region, or indeed just a greater concentration of stars within the arms, but they don't appear to be local stellar objects, because they don't resolve to a point of light.
  11. BiggarDigger

    Cirrus or a Galaxy?

    I managed a short session last night (31st August) which reminded me to always keep one eye on the bigger picture. Out at 9:30pm under veiled skies still brightened by the setting sun. Still, it allowed the 200p to cool down a bit and my vision to adapt. It was cold enough to need thermals and my winter coat (we are abut 225m above sea level and the nights here can be quite chilly even in late summer). Seeing wasn't good with lots of cirrus floating around, but Clear Outside suggested an hour or two of decent seeing so I persevered. Mars was very bright but shimmering too much at low elevation for a good view. Jupiter was just setting. We have good clear views of the horizon from the East all the way round through South to the NorthWest, with one exception: a 10m Sycamore tree just into the farmers field beyond our boundary about 10 degrees west of South. Unfortunately Sagittarius falls into this "hole in the sky" at this time of year, so I decided not to even try and swung the dob round to the North East to find M31 and its companions. Visible to the naked eye, I was hopeful of catching a few other much fainter galaxies in Andromeda in the eyepiece, but alas the cirrus was blotting out too much to see anymore than M31, M32 and M110. Swing down halfway to the horizon to look for M33, which is one of my "calibration" objects: If I can see M33, then I've got a reasonable chance of picking out other difficult objects. Align on the pointed tip of the Triangulum asterism and begin to star hop up and to the East but the cirrus is getting in the way. By now it's well past 10pm and the skies are as dark as they are going to be, with the moon not far from the Eastern horizon and the ever increasing threat of cirrus, I'm thinking this might be a bust. I stood back from the eyepiece to look around and cursed the line of cirrus hanging there from the South round high in the East and heading to the North, just to the North West of where M33 should be. I decided to wait 5 minutes to let it pass and after a while, I realised it wasn't moving and that it was in fact the MilkyWay! I think the hedgehog shuffling around in the bush learned a few choice Anglo Saxon words as I went back to the eyepiece, this time, to find a gorgeous M33 fully visible even without averted vision. Spending time on M33 is really worthwhile as there is so much detail that can be teased out under good conditions, so I let as many photons tickle my retina as I could; just about seeing structure with arms sprawling out from a grainy central fuzzy core. Having satisfied myself on M33, I swung up towards Cassiopeia in hope of finding some of the much fainter NGC objects in Triangulum and Andromeda, but alas, came up blank. Down to Perseus and the double cluster is visible to the naked eye as a faint grey smudge and two grey smears in the finder scope. Lovely view through the dob. West to look for the Heart and Soul nebulae, but knowing that these will be difficult to find in the scope as they are so diffuse. Nothing shows and the stars in the MilkyWay are fading. I looked up and a shelf of cirrostratus was moving in from the west getting thicker the further west I looked. Ursa Major was gone and within a few minutes Cassiopeia was fading too. I waited a few more minutes hoping a break might form, but when the moon appeared above the horizon, I knew it was time to call it a night. Lesson learned: always keep an eye on the sky: that bank of cirrus cloud might just be a galaxy! (and I must apologise to the Hedge Hog when next I see him) Richard
  12. I doubt that it would be possible to correlate the times against the data that you have in it's current form. There's no duration information on any of the events. Try connecting the output of your .wav files to an oscilloscope (Spectrum Lab software should be able to do that) and look at the varying DC offsets coming out. You might be able to derive a the doppler shift, if any, on the FM detector of your radio. Bear in mind an FM detector will show a shifting DC bias when presented with a carrier wave signal subject to Doppler shift. Armed with that, you may have some info on duration and profile of the reflection. That might be possible to correllate against other signals or detections. But to be honest, I think it'll be a long shot due to artefacts introduced by the recording codec used to generate the .wav file. For now though, I think all that can be said is that the clicks are consistent with what I might expect for detections using an FM demodulator. Hope that helps, Richard
  13. I'm still getting detections, though the peak appears to have subsided from this morning for me. This is the detection rate since yesterday lunchtime when I discovered the radio had de-tuned itself: Shame about the equipment fault. But useful info nonetheless. @Coto: I listened to the audio file, but all I heard was a single very brief click. One the otherhand, that's what I would expect for a carrier wave detection on FM. You'll get a small, but fast decaying dc offset created by the FM detector, like a spike with a post-attack slope. It won't carry any audio as there's no FM modulation. The spike will be caused by the initial strike followed by the decay caused by Doppler on the signal, but the frequency change is small and very fast, so the FM detector output would would just be a click I think. You might be able to see a reverse saw-tooth waveform from on an oscilloscope, which would help confirm if they are detections.
  14. Dagnabbit!!! I nipped home at lunch to see what the detector had recorded for the rest of the morning and noticed the HDSDR was way off tune. How long it had been like that is anyone's guess, but I wouldn't be surprised if it went off tune just before midnight! Tuned back on frequency....and I have meteors again, not many, but they are there... So, I might look for other RTL control software to feed Spectrum Lab. Still, it was fun putting this together over the last week and a great learning exercise. Perhaps I'll make time to re-engineer it over the coming weeks. Richard
  15. Hmmm....something rather odd happened at my site. Did they switch GRAVES off, or did the rain get in the way, or what? My hourly totals tanked around midnight local time and stayed low all night: I'm not sure if it's instrumentation error, or a real effect. I'm rather conflicted between disappointment and curiosity about what happened. Very strange.
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