Receiving NOAA Weather Satellite Images with RTL-SDR

Orbiting Earth are 3 weather satellites operated by NOAA (National Oceanic and Atmospheric Administration). These satellites happen to transmit images back to earth in the VHF band at ~137 MHz which with a cheap TV dongle can be received at home relatively easily. Personally I have never had much luck up until now and with the correct software, can be automated which makes things that little bit easier. Currently only NOAA 15,18 and 19 are operational and for me anyway I get 6 passes each day of varying elevations.

So what sort of antenna will I need? Ideally you will use a Turnstile antenna or QFH antenna as these are circularly polarised and also receive signals from the sky quite well. A V-Dipole can also be used and I have received weak signals as low as 8° above the horizon. Yagis can be used but will need a rotator to track the satellite or this can be done by hand as they are very directional. Ultimately a V-Dipole is by far the most simplistic to build and a set of TV “rabbit ears” could also be used. The telescopic dipole kit from rtlsdr.com will also work in this case.

From a software standpoint you will need the following; SDR# (available from https://airspy.com/?ddownload=3130), Orbitron (available from http://www.stoff.pl/) and WXtoImg which you will use to generate the images from the received audio can be downloaded from (http://www.wxtoimg.com/) Some form of audio piping method such as Virtual audio cable or similar is also needed to feed audio from SDR# into WXtoImg.

The setup info for the software side of things is available at https://www.rtl-sdr.com/rtl-sdr-tutorial-receiving-noaa-weather-satellite-images/

Building a V-Dipole is pretty straight forward. You will need two 53.4 cm long lengths of 3mm thick aluminium wire, a screw terminal block capable of fitting onto the 3 mm wire, some coaxial cable to run between your antenna and SDR dongle and a place outdoors with an unobstructed view of the sky. Each leg should be bent into a V shape 120° apart. Ideally you should mount it in a north/south direction as shown below. I reversed the direction that Adam-9A44QV has suggested due to me being located in the southern hemisphere. I’m not too sure if that matters but never mind.

SDR# should be configured to receive WFM with a bandwidth of 40 kHz or so to allow for Doppler shifting of the frequency. The first satellite I managed to receive was pretty weak and although I could clearly see the APT signal in the waterfall view of SDR#, I could only just make out the tones by ear and wasn’t able to decode any images from that particular pass but eventually I got something. The APT signal looks something like this. HDSDR works better in my case as SDR# has problems with choppy audio on my machine for some unknown reason. Either way the settings are the same. Audio sampling errors I found cause the image to be completely unreceivable due to loss of sync.

Decoding the image is somewhat similar to decoding SSTV but the quality is far better. Ultimately the higher elevation the satellite passes, the stronger the signal and ultimately the image is clearer. With low passes, I can see the signal appear and disappear as it passes behind objects such as nearby tall buildings and terrain features such as hills. I’ve even seen the signal strength follow the pattern of gaps between a few nearby buildings as the signal either passes between them or is shadowed by said building. The images for me have a slight slant which is easily corrected for using the slant adjustment in WXtoImg. This slant is caused by the Doppler shift of the signal frequency. If all goes to plan you should be left with an image such as this. From here false colour and other enhancements can be made in WXtoImg to produce images like the weather service does.

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