John's Musings


Yeah, Me Neither

Tracking NOAA Satellites And Shit

If you wonder why I add in "and shit" on a lot of my web page titles watch Mr. Lahey on The Trailer Park Boys and you'll understand fully.


All day, every day three operational NOAA satellites are buzzing overhead transmitting data back to earth. Most of the pics you see on the nightly weather are from NOAA satellites. Anyone can download this data. It is an Automatic Picture Transmission (APT) signal that is somewhat easily decoded.


LET ME STATE FOR THE RECORD HERE THAT I'M DOING THIS THE HARD WAY. IF YOU HAVE A STATIONARY ANTENNA SUCH AS A QUADRIFILAR HELIX ANTENNA (QFH) IT WILL DO ALL OF THIS AUTOMAGICALLY IN A PROGRAM CALLED WXTOIMG. YOU DON'T EVEN HAVE TO BE THERE OR DO A THING.


This whole evolution for me is about understanding satellite orbits, azimuths, elevations, doppler shift, etc. Plus I'll say this about using a handheld antenna and doing this in the way I describe below...........You get better results! I think my grabs look as good as anyone's..........yeah there are some guys with stationary setups who crank out better stuff but ask them how much they spent.


What you need:


A laptop running Linux (or Windows, but I hate Windows)

An SDR dongle (any one will do) Try this one. I only picked it because it was pretty cheap. You can get these on eBay for a few bucks.

An antenna. You can make one for almost free but you need something tuned to about 137 MHz. I bought this one. The price is OUCH but if you want grabs like this, you'll pay the price.




Hurricane Irma and Jose, September 10th 2017



The software you need is all free. You need:


GQRX


Sox install with sudo apt-get install sox from a command line in Linux


WXtoIMG


GPredict - This is optional but it shows you when the satellites are a comin'. If you look in the upper right corner it will tell you NOAA 18 is coming in 8 minutes and 22 seconds. It will also populate on that globe and show you where it comes into acquisition. North or Southbound. Then you have a rough idea where to point the antenna. Before GPredict will work for you, you have to set your location. (Same with WXtoIMG) Google up your latitude and longitude. You'll need it for both programs.



Before you grab the antenna open GQRX and set the frequency from information you get in GPredict.





Open GQRX and configure and select your SDR dongle here under the Device drop down. Your mileage may very depending on what device you bought. A generic dongle typically looks something like this and typically the defaults are okay. Click OK.




Now hit play on GQRX. There should be no signal until you get it locked in. Set your filter width to about 40K, your mode to Narrow FM and figure out where you are recording to. Mine just records to my Home Directory (/home/john). Notice the gray width around the red vertical line below the 5 in the picture below. That's not very wide and will be tough to see your signal. For this reason I use a FunCube Pro Dongle usually which has an input rate of 192000. If you look at the pic above you are at 1800000. Anyway because the FunCube Pro doesn't display as much bandwidth across the scale the signal looks huge and it's much easier to see. In GQRX you can use the Zoom feature under the FFT Settings tab.




Okay, now you're standing there like a goof pointing an antenna in the sky hopefully in the right direction and you should be hearing and seeing the signal soon. Again in my video below I have that huge signal I don't have to zoom in on. Make sure and hit the record button but only when you have a good static free signal. Try to keep the red vertical line exactly in the center and know that because of all number of things the frequency will never be dead on and you may even have to look around a bit to find it initially. Also once you do get centered on that signal due to a phenomenon known as "Doppler Shift" you may have to make some adjustments during the grab to keep it centered. The signal will drift a little on you.


A good pass lasts about 15 minutes but you're generally lucky if you get 10 to 12 minutes. Remember to resist the urge to record that static. Wait until the signal is strong to record audio. And bail out at the end of the grab before the signal starts deteriorating.



A few points about my video above. It is a couple years old and the GQRX interface looks SLIGHTLY different. On the video the record button has a red circle in it. On my pictures it's a gray button that says "REC". Nothing earth shattering, but different.


Trust me when I tell you that you need to do this a handful of times before you get the hang of it. If you nail it the first attempt.......You Da Man (or Da Woman). It's a little tricky to say the least especially since you have to follow the arc with the antenna keeping a good strong static free signal. Over time you will figure out where to point, how to twist the elements, etc. It's an acquired skill.


Now you have an audio file that must be processed. Open the directory where you saved the file and find it. Here's mine below. The file name is:

gqrx_20170910_122412_137914900.wav


Or basically GQRX + Date + UTC Time + Frequency




Now lets convert that file by passing this command for sox to change the rate to 11025 Hz otherwise the file is useless to us. Notice after the file name I named it noaa30.wav. You could name it anything you want "noaarocks" your girlfriends name, 1234......whatever you want.


sox gqrx_20170910_122412_137914900.wav noaa30.wav rate 11025




Now you have a file that can be opened in WXtoIMG alas there is a problem. If you open it by File > Open Audio File the map overlay WILL BE WRONG.



Think about this. The positioning of the map is determined by what the time stamp on the file is. When I converted the file I gave it a brand new timestamp. The time at which I did the conversion, not the time at which I did the satellite audio grab. This is what happens. Pay particular attention to the Great Lakes. See the satellite capture of Lake Michigan? It's in freaking Indiana, Kentucky, and Tennessee. Whoops.




Go back to after you created the noaa30.wav file. Now lets transfer the time stamp from the original file to the new file. Do this:


touch -r gqrx_20170910_122412_137914900.wav noaa30.wav





Now it's all good. Hurricane Irma is exactly where she is supposed to be in the pic below. And Lake Michigan is where it is supposed to be as well (not depicted).




You grabbing satellites and shit.






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