Automated Screenshots

I'd like to see the changes in propagation and in the RFI over long periods of time - it seems to me that a quick visual check on that would be by gathering a set of 'snapshots' of the waterfall.
Any thoughts on how to do this in a simple way, without tying up my personal machine?


  • I added automatic snapshots to the IBP extension a while ago.

    So adding other similar features is quite possible if there is a need. How would you like to see it work?

  • Wow - that's neat! I had no idea about this feature. I have to poke around to see what it did. It should have generated those JPGs, once per change in beacon, and saved them on the Beagle, right?

    What I was looking for was a series of periodic snapshots of the entire 0-30 MHz spectrum over a day. I'd be able to analyze or compile them into a GIF to see the slow patterns in propagation, shifts in the power/frequencies used by transmitters, and the changes in the local RFI. 

    Ideally, I could have this done without needing to keep a receiver instance running that entire period, but if this gets me most of the way, I'll take it and be glad since I don't know that many other folks would have need for this sort of feature.

  • You can manually do that with the right click menu now - saving the current waterfall when you want.

    The automatic beacon save works every 3 minutes after a full cycle of all the beacons on a band.

    How long a snapshot would you want in each image? I could automatically compile multiple shots in one jpg or png. Perhaps 30 seconds of waterfall once an hour giving a single set of 24 images after a day. The alternative would be 24 separate images taken at one hour intervals showing 30? seconds of waterfall. You could convert to an animated gif.

    There is a problem with saving images which is browser specific. Different browsers have different limits on the total file size that can be downloaded. I have been waiting for feedback to see if this is an issue and how to tackle it - by limiting the history time, or limiting the bandwidth or degrading the image. 

    Another possibility is one I am currently adding to the IBP extension which is a collection of mini-waterfall images that shows each beacon in a box.

  • I see the autosave feature, I get it now. I see that when you record the cycle that you get four images, one for each band. I tried running the extension to snapshot the entire 0-30 MHz; I zoomed all the way out, set it to Cycle and Autosave and waited. The first run is OK, the image is a bit long. After that first cycle, the receiver zooms in to focus on one of the IBP frequencies. 

    Anyway - as for the amount of waterfall,  just enough to tell the difference between modulated things, normal variation in band conditions and RFI. Maybe 10 - 30 seconds; 10 being that 'strip' the extension usually records for each beacon and 30 the whole 'sweep' of the waterfall. No more than that.

    What would be the least effort to get my little use case? I can live with the length of the resultant images and the multiples; if there could be date/time added to the file names, and there was some way to maintain the zoom level from one cycle to the next so that I can stay zoomed out for a whole day, I can handle it from there.

  • The current project is to finish the IBP scan features. Then I will look at how to extend it for your case. Here is where I am going now:

    I should have it ready to merge for John tomorrow unless something falls apart :)

  • I'll be glad with what I can get. Thanks for thinking on it.

    take a look. Once John merges, let me know if there is anything I can change to help you do what you want to do.


    You can capture 10 seconds to 2 minutes of waterfall on intervals of 10 seconds to 1 hour. That should be flexible enough for many applications.

  • Oh wow, can't wait to try it out!
  • You can try it on my kiwi

    Apparently some of my code wasn't compatible with some browsers, so I am testing locally first.

    Good chance to catch bugs or other browser problems I don't see here.

    - Peter

  • A couple things. One is that on Firefox, the spacing of the checkboxes is a bit off. Second is that the saved file name could use a timestamp added to it.

    I'm going to leave this running for a while.

  • Video from series I took from your kiwi.

    Spectogram from VE3SUN

  • Video is with 10 second snapshot every 3 minutes.

    Having had the experience of using ffmpeg to turn this series into a video, it was convenient that all the filenames were the same but for a (n) enumeration. While it would be useful for each filename to be timestamped but it would be a shame to lose the convenience. In the interest of keeping to least-effort, I'm good with how it is now and let some other compelling use case call for improvement later.

    What would it take to append a frequency scale on the extension?
  • Interesting that firefox seems to squeeze the extension window. I will check that later.

    I will look into alternate filenames for you. I would like to put more info in an exif, but don't think that capability is easy in the browsers. Will see. It shouldn't be hard to label the edges as well as the center of the waterfall. Right now that info is in the filename.

    I think we can go with the current version and I can tinker with it later.

    Your video doesn't seem to be there,
  • Click on the text 'Spectrogram from VE3SUN' above.

    Or here:
  • Nice. I will have to correlate the broadband noise with our furnace running.

    I have sent the merge request to John.

    BTW, Faststone Image Viewer has lots of batch rename features that can help prepare files for FFMPEG time lapse creation. I used the combination a lot in some previous projects making full night videos of stars and auroras.
  • Based on your idea, I did a time lapse view of the broadcast band during this mornings gray line transition from dark to light. Interesting watching the change from DX to local stations over that period. With Faststone you can just hold down the PgUp key to zip through the images in a few seconds, so no need to use ffmpeg unless you want to post the video.

    Thanks for the idea!


  • Those wide bands at 15 and 17 MHz that seem to shift up and down to the same two or three positions are interesting. Corresponding to the lights being turned on and a room warming up? I look forward to seeing these things on our own installation rather than your house. ;-)

    I am also wondering on how this might facilitate monitoring Jupiter radio emissions.

    Lots to play with - thanks for making this happen.
  • edited November 2017
    What a coincidence. I was just thinking about listening for the Jupiter emissions last night as I was driving home.

    I haven't listened to them in a while - like 55 years! Yikes.

  • I have added a scale for you...

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