Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

sgl_imaging_challenge_banner_supernovae_remnants_winners.thumb.jpg.a13d54fa405efa94ed30e7abd590ee55.jpg

BiggarDigger

Members
  • Content Count

    129
  • Joined

  • Last visited

Community Reputation

160 Excellent

About BiggarDigger

  • Rank
    Star Forming

Profile Information

  • Gender
    Male
  • Interests
    Astronomy (obviously!), IT (work - ugh), electronics and radio engineering, meteorology, fresh air and wide open spaces.
  • Location
    Biggar, Scotland
  1. At that band, a 3.2m dish is probably the smallest practical size and even then, depending on the mount and base, you may be in danger of giving yourself additional engineering challenges that could be removed by going to stacked and bayed yagis. A 3.2m dish should yield a forward gain of around 20-22dBi at those frequencies, which is probably a couple of dB less than an array of four 15 element yagis stacked and bayed, or a multi-element phased array. Given the size of the yagi, the array is pretty small, lightweight and has very little wind loading, so a simple ground pole with az-el control should match the dish. Better still, if you can just arrange elevation control, you can run drift scans across your chosen target, so the mounting arrangement becomes considerably less complex. However, don't underestimate the stacking and baying phasing and accuracy to achieve an optimum solution and if you want to go for circular polarisation, then such a solution is not viable. If you decide to go with the dish and it's already mounted and driven, a small 2 or 3 element yagi, centred on the 432MHz amateur band may suffice, mounted on a suitable A-frame. You'll need to get the spacing correct from the front of the dish to the driven element and a worm drive may help tune that for optimum gain/bandwidth. The smoothness or finish of the dish is surprisingly tolerant to surface defects and abnormalities, especially at such low frequencies, so if you need to attach additional brackets for the mounting frame, these should make little difference to the performance. Circular polarisation should give you good coverage and some years ago there used to be amateur radio satellite antennas available in that band. I see no reason why these shouldn't still be available from various suppliers. Try to use the lowest loss co-ax feed as you can afford, even with the LNA mounted at mast head. Good luck! Richard
  2. That's great James, really pleased for you. My heat map looks a little different, but I'm cautious: the numbers seem quite high, even for the peak of a shower. The peaks in the evenings of the 20th and 23rd may be noise radiated by next door's heating system. That said, beyond the obvious curious evening peaks in my data, there are some similarities. The "switch on" of incoming strikes on or around the 17th/18th, the background rates and the relative lack of strikes in the evenings of the first half of the month are similar in both sets of data. I'll need to look more closely at my data to see what those evening peaks represent. Richard
  3. Yes, a warm welcome Geminids! I'd second what Ian says, a higher rate sampling is needed to accurately record the transient head echoes. That implied a shorter FFT window and more experimentation with Spectrum Lab. Unfortunately, lack of time over the last couple of months meant I didn't progress the idea. There may be issues with aliasing at high sample rates and fast transients: Could be interesting nonetheless. Here's a couple of incoming strikes with clear head echoes that recorded as I type: The problem here is noise. Taking the first return (on the left of the image), at what point does an algorithm detect the start of the head echo... 1, 2, 3 or 4? Point 4 looks like noise, but is on a possible extended line from point 3. There is "something" at points 3 and 2, but are they signal or noise? Point 1 is clearly in the head echo on this return, but the signal is now strong enough to blur into adjacent pixels (time), reducing the accuracy of any measurement. Much higher resolution is required, but, as noted, that may make the FFT sensitive to the discontinuities in the GRAVES Radar signal. I suspect a quantitative rather than qualitative approach is needed to save being bogged down in noise and spikes. Richard
  4. A short session tonight: The first for nearly two months, due to broken ribs (mine not on the scope or mount!). I'll spare you the detail, but tonight is the first time I've been able to hug the scope properly, let alone lift it. Still, it was clear, not too cold and I'm busy the rest of this week. It was probably my last chance before full moon, so it would have been rude not to! What followed was a gentle procession through Virgo just drinking in the galaxies almost as if through osmosis. I wasn't too concerned about keeping track of which one were which. Heresy, I hear you say, but I was just glad to be out with the scope under the stars again. I did spend a bit of time looking for 3C 273, but I'm a bit rusty with star hopping and tonight wasn't well planned so not much hope of finding it, but it was good to be back in the saddle again. With a bit of luck, the end of the month will hold clear skies and I'll be able to try once more before the season closes for the summer. Richard
  5. I'm at 55.5N and the season has one last hurrah here. I've just been out for an hour or two and even with a 20% waxing moon the sky is bright. Full moon in 10 days puts me back to late April/1st week in May which is really the last chance for DSO work until late August. Clusters are just about doable over the summer and planets too, but as has been noted, the planets are very low so not good seeing for a while. If you get bored with the dob, let me know, I'll be up the A90 in a jiffy ? Richard
  6. Now, that is definitely a meteor! Well done!
  7. My guess is that they are predominantly as a result of rear lobes. The front lobes illuminate the sky at an altitude of 90km well over your southern horizon. It's possible anomalous propagation could result in back scatter reaching you from the frontal lobes, but there are two generally accepted modes that would provide that path: Tropospheric ducting or Sporadic E. Neither modes are open right now between Scotland to southern France. In fact, I'm not sure tropo would even allow for such propagation because the incoming signal originates in the ionosphere, above the troposphere and may not be able to break into any super-refracting duct from above (the process that keeps the signal leaking from a duct may prevent an external signal breaking into a duct). On a positive note, I find the number of detections recorded at my site drops dramatically in the presence of disturbed weather, such as we have just now. This suggests that when weather conditions are more favourable (a calmer troposhere), your detection rate could increase. It will be very interesting to see how your detections develop as we proceed through April to the Lyrids. If you can run one of the published algorithms on Spectrum Lab on the laptop, you can build a record af background rates, which could be useful if you are able to get the Pi based detector running in the future. Richard
  8. Certainly does look like a meteor. Well done, congratulations! It's difficult to completely interpret without time and frequency scales, but the apparent Doppler shift of the head followed by the intense body is classic meteor. That's encouraging to see. Hopefully you get a few recorded events overnight when the background rate peaks. Richard
  9. The range to the hills from Stornoway shouldn't give rise to too many issues. The signal propagating from the reflection media will have been refracted and dispersed through the ionosphere and troposphere already. The may be some additional distortion, but the Scottish mountains are generally flat topped rounded hills (and quite wet most of the time too!). It's possible more bifurfication of the signal could occur however. The Icelandic VOR beacon is a very interesting proposition. The beacon at Akureyri is on 113.6MHz which is a nice frequency to use for meteor detection as it will scatter well. It's radiation pattern is ideal for these purposes and, additionally, it's a good range being approximately 1100km, which is a magic number in this context. It means you will be able to see a 90km altitude at Reykjavik on your horizon and a forward scatter common volume will exist all the way from your horizon to your zenith, giving you a large reflecting media to capture incoming meteors. A broad beamwidth vertically polarised antenna pointing northwest from Stornoway should have a decent chance of detecting meteoric reflections from that beacon. You will undoubtedly have interference from auroral scatter which will lead to blurring. Auroral scattering will be quite prevalent at your latitude, but auroral scattering is fairly wide wideband and quite different to the narrowband meteor scatter you are looking for. Audibly the narrowband Morse or voice signal will be blurred into a broad hissing noise. Even though your current antenna is tuned to approx 144MHz, it may be worthwhile turning the antenna to the northwest and see if you can hear that beacon via the Aurora, taking into account auroral forecasts and timing it to an increase in auroral activity. We are close to sunspot minimum, but there are still plenty of visual Aurora reported visible from Skye and other northern locations. If you can hear the beacon via Aurora, ther is a very good chance of obtaining meteor reflections off it. I would be tempted to look for it myself, but my antenna is mounted on the SouthEastern side of the house and totally blocked to the NorthWest. Richard
  10. Apologies, I've been out of circulation for a few days. I don't think the gain of the antenna is a major part of the engineering problem when listening for GRAVES: the antenna I use is a simple 2 element phased array (an HB9CV design https://www.qsl.net/dk7zb/HB9CV/Details-HB9CV.htm) with forward a gain of 4dBd (around 7dBi). Clearly the GRAVES radar transmits are very strong signal, so a 3 element yagi will do fine if you can see a main lobe common volume via line of site. Your topographic profile shouldn't present much obstruction with a clear line of sight over water to the mainland. The arithmetic however shows the forward lobes of the radar are well over your horizon, and for me too. From other work, we have deduced there are likely to be reasonably strong rear facing lobes and sufficiently high angles for me to detect forward scatter in a northerly direction. However my site is 350km further south than yours, which significantly alters the geometry of the common volume compared to that for Stornoway. The maximum range to a 90km altitude is 1100km (line of sight) which, for you, is over Southern England and Northern France. Although there appear to be rear facing lobes, I suspect these are not strong enough at the required angles to achieve echoes that are resolvable with entry level equipment at Stornoway. Having now established your dongle is quite well tuned, you could try look for meteor scatter signals from GB3VHF. Although this is running much lower power than the expected signal from GRAVES, that could be compensated for by increased gain in the receive antenna. I wouldn't recommend stacking or baying antennas for 144MHz in the first instance: doing so poses real engineering challenges getting the phasing correct. It will also significantly reduce the 3dB beam-width and place deep notches not far from the centre line of the antenna. A small azimuth or elevation misalignment of the antenna could easily reduce the received signal dramatically. A modest single 9 element yagi (https://www.radioworld.co.uk/220309_tonna_2m_9_element_yagi_antenna_144_to_148_mhz) will give decent forward gain and broad beam width to be able to look for GB3VHF. A mast head preamp could also be beneficial as the signal may be quite weak. These should give a reasonable opportunity to receive meteoric signals from GB3VHF. The challenge will then be to adjust the detection algorithms for take account the non continuous nature of the signal broadcast from GB3VHF. To capture signals from GRAVES, I use SDR# and feed the audio into Spectrum Lab. The primary reason for this is that Spectrum Lab refuses point blank to drive my dongle. I suspect there is a non-standard build in my dongle firmware, but it's overcome by using SDR#. To connect SDR# to Spectrum Lab I use a free virtual audio cable from https://www.vb-audio.com/Cable/. This arrangement works well, even though SDR# uses more CPU than I would like. There is an advantage to this method too: you are operating a configurable receiver via SDR# and can optimise parameters such as gain, bandwidths, noise blankers and notch filters using a much simpler GUI than through the configurations in Spectrum Lab. Here's a screen grab of my SDR# configuration: I now use a tweaked version of IanL's Spectrum Lab detection algorithm which gives good results for me. Overall it works well, as can be seen with a satellite detection as I type: My honest opinion, given what we know and/or have deduced about GRAVES, is that its south facing lobes will be too far away and well over the horizon from Stonorway. Any north facing lobes will be difficult to use at such extreme range and a closer north facing beacon such as GB3VHF may yield better results even if there are still limitations. Richard
  11. It is possible to use amateur radio beacons for meteor detection. In the past, I used to operated amateur meteor scatter and would often hear signals from such beacons. However as has been noted, amateur beacons are typically low power and illuminate smaller volumes of the sky. Reliable detection of signals from these beacons may need higher gain antennas. The non CW nature of these beacons does mean you may miss a number of incoming meteors, including the head echo of long duration events. But if your range to GRAVES is too far, they are an alternative worth trying. Richard
  12. OK, that makes much more sense James: I assumed you wouldn't be up overnight starting and stopping the script. So, anyway, it looks like the trigger for the event is set at 17dB above noise, that may be quite high, especially out of a shower. Try changing the line if( Sig>(A+17) ) then C=C+1:D=D+1:timer0.restart(2) to if( Sig>(A+12) ) then C=C+1:D=D+1:timer0.restart(2) That's 12 dB above noise. Experimentation is important here, the lower the value, the more false triggers you may experience. You can, if you want, also tweak the "low" and "high" values to be tighter to your expected 2kHz nominal value, again reducing the likelihood of spurious triggers. At present it's quite wide looking over 1 to 3Khz for anything above 17dB SNR. The other thing to check is does the c:\spectrum\screenshots folder exist after the re-install of Spectrum Lab? If it doesn't the screen capture will likely fail. There's a whole discussion to be had on what is a spurious trigger. Some people like to have close to zero background and only capture the large, loud and long echoes during a shower. Others (like myself) like to see the background rate too. I have a lowish signal to noise trigger limit but a tight frequency band. There's probably no right or wrong, just different. Richard /edit I just looked a bit more closely at the script James. You could also tweak the timer values if necessary. timer0 appears to be used to prevent multiple triggers on events that follow each other less than 2 seconds apart. Probably OK but you can experiment with the value. timer1 appears to be a delay of 30 seconds after the trigger before a screen shot is taken - depending on your waterfall plots, that may never capture a signal. Set the delay to be suitable for your waterfall scroll rate. Hope that helps.
  13. I assume the log reads as follows: Time, event count, peak signal, noise floor, peak signal frequency, duration. If so, the logged event count looks odd for the last three. If the assumption is correct, event count should increment once per echo logged, as per the first six events, then resetting to zero on midnight (which it appears not to do - the 6th event is after midnight). What frequency are you tuned to on the VFO? - that will tell you if the 2kHz signal is likely to be GRAVES. Also, what units is the duration measured in and can it be made more granular? Depending on the continuous actions script, you may have 9 events: 6 between 1 and 2 seconds duration and 3 events between 0 and 1 seconds, or something similar. However, it could well be that the script is not functioning as it should - no screen captures and odd looking event counts. I'm not sure if your script takes into account that Spectrum lab requires double backslashes \\ to represent a single backslash in the path variables, i.e. C:\Users\Richard\Desktop is represented as C:\\Users\\Richard\\Desktop. A typo there could easily break the ability of the script to write screen capture to the disk. And yes, I completely sympathise, sometimes it can be very frustrating getting everything setup just right with no reference to work against: but it does looks promising, and perhaps with a few tweaks and a bit of debugging you may have a functional system. Richard
  14. That sounds much better James. Fingers crossed you should now be seeing some background rate meteoric signals. You may still need to tune the conditional actions script to optimise detections. Richard
  15. The detection of Morse signals on 144MHz amateur band is encouraging. You could take a look for specific beacons listed here: https://www.microwavers.org/maps/2m.htm to see if you can identify the station and use that as to verify the SDR tuning accuracy. Background meteors will peak in the Lyrids shower on the 23rd April which should give a good indication of any possible common volume for GRAVES or even GB3VHF as the transmitter station. Richard
×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.