Decoding NOAA Weather Satellite Transmissions!

I stumbled upon information about the free version of WXToIMG software that said it would automatically decode transmissions from certain NOAA weather satellites.  Curious, I wondered what specialized equipment would be required for this.  Thoughts of some NSA or CIA or NASA listening station ran through my mind.  Having more time than equipment over a Christmas 2013 vacation I decided to give it a try.  The short explanation is the image below captured using a Yaesu FT 857d radio, 2 meter Diamond 8 db gain antenna, LMR 400 coax and a newer model Dell laptop computer connected to the ham radio via a SignaLink USB.

NOAA 19 at 28 Dec 2013 19:18:18 GMT

You should see two images side-by-side.  You should also see good maps of a good portion of the US and Canada.  While there is some noise in the images try and find the Wisconsin state.  There you should see a yellow +.  For the software to operate correctly you have to input the latitude, longitude and altitude above sea level of your listening station.  The software then shows, with the +, where that location is on the world map.  If the + is in the wrong spot then you know you have an input error.

You should also be able to see white rather wispy cloud deck going roughly west to east over much of the northern US states on the image to the right.  That cloud deck has progressed further south on the image to the left.  This image was taken on 12/28/2013 and defines a weak front with a blast of sub-zero arctic air plunging in behind it.  Wind-chills the next night here in Appleton, WI were predicted to reach 20 to 30 below zero.

So that’s the quick and dirty image.  Here’s some description of how the software operates and then some information on how you can capture much more impressive images if you choose to make the changes.

How The Software Operates

A simple click of the RECORD File menu option starts the software listening.  At the bottom edge of the window it tells you what the current UTC time is, what the next satellite to pass by will be, what frequency it will be on and when it will come into strong enough decode reception range.  How does the software know what satellite will be flying overhead?  You do have to download free keplerian elements.  What the heck are those?  I think of those as predictions of the flight path of the satellites.  They change over time as orbits decay not always as predicted.  Because of this it is quite wise to download a fresh set of this free data every day or two.  The download and automatic install process is very fast with a cable modem.

For each pass I was able to hear the bird on the radio before the software started the decode process.  There are a wide variety of decode options and I won’t go into those here – get the software and check the menus for that.  It’s free to start.

The software converts the sounds coming from the satellite via the computer’s sound card to data that it displays on your computer screen.  It does this one very thin line at a time.  Now I didn’t time the full decode process but I would guess it’s like 5 – 10 minutes.  First the raw image is captured and then the image is processed.  The capture process is pretty boring after you have seen it once.  The processing process is pretty interesting with various images being displayed in relatively rapid succession as it produces various versions of images and applies maps, etc. to the images.

That’s an overview of the processing that takes place.  For specifics review the software documentation.

How To Improve Image Quality

This isn’t rocket science.  Well – since we’re dealing with data from satellites launched by rockets maybe it kind of is…  chuckle.  The decode process starts with the reception of the signal at the antenna.  You can’t do anything about the strength of the signal.  You can do something about getting as much of that signal to the radio as possible.  Enter the antenna.  I used a vertically polarized antenna.  The software documentation suggests using a circularly polarized antenna.  The software website provides links to several – figure $200 for a descent one.  You can get much more elaborate with expectations of more quality with increase in cost.

Next comes the suggestion to consider a signal pre-amplifier.  The software website has a link for suggestions for such a device.  About $75 if memory serves.  This would increase the strength of the signal delivered by the antenna to the coax.

I used LMR 400 coax which is relatively low loss coax at these frequencies.  Careful research into coax is suggested.  Signal losses in coax can be substantial and spending a few additional dollars here can provide big benefits.

This brings us to the receiver.  I used my ham radio which has a pretty sensitive receiver.  I did not research how this radio compares to specialty receivers, scanners, etc. that could also be used for the process.  If you have a scanner or other radio, the software if free to start – give it a try and see what quality of image you get.  Or – consider the cost of a radio vs your checkbook size.  Make sure to remember to keep filters OFF as well as DSP so that you process the pure full signal.

Now comes the connection of the radio to the computer.  I used a SignaLink USB to do this.  This provides isolation and also provides some processing controls.  Some may prefer to go direct.  Do at your own risk.  Others may prefer higher-end (read more expensive) devices like a RigBlaster, etc..  Again – determine what connections your radio and computer needs, what your budget is and what your performance expectations are.  I am not one to claim that my solution is the absolute best, etc..

Next comes the computer hardware.  See the software documentation for specifications of minimum computer required.  Then comes the software.  The free version works.  I have read that you should NOT upgrade to the paid version unless you already have a reasonable image decoded.  In my instance I think it may be worth it.  But – there are no refunds.  The paid version may be able to control your radio through rig control.  Check the documentation.  It will control my radio.  I have read that the paid version may produce substantially better images.  See comparison chart on the website for feature comparison vs free version.


Out of curiosity this was a fun adventure.  I also found out exactly what some of the sounds I have heard during my shortwave listening radio days in the 1960’s.  Back then I heard something that sounded like sonar.  Having no internet and knowing no ham radio operators or Navy personnel I could only wonder what those sounds were back in the days of the Cold War with the Soviet Union.  I was probably 8 years old at the time.

Going forward, I ask myself what the value of dramatically enhanced images would be to me and what that performance enhancement might cost.  I also have to ask what the quality of images might be compared to those that I might be able to find on the internet.  My guess is that directly decoded images can be of higher quality than those compressed and cropped for display on web pages with limited storage and display space.  I doubt there are many full pixel images available on the web.  I may be wrong.  Chime in if I am please!  In the end it’s sort of like asking a fly fisherman why he ties his own flies when he can go buy them!  I realize there are a lot of other considerations besides budget and the joy of doing it yourself in that discussion.

Until the next time – stay radio active!



Jon Kreski – AB9NN– Appleton, Wisconsin / Green Bay, Wisconsin / Oshkosh, Wisconsin area

Member – Fox Cities Amateur Radio Club (FCARC)

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