Every minute of everyday that goes by, the earth's surface is scanned by a decade of weather satellites. They photograph a 1 km wide strip of the surface below, convert the image into a fax-like datastream and broadcast it live, via radio link. With suitable equipment the signal can be intercepted and converted back into a picture. You need:

  1. A receiver that covers 136-137 MHz in FM with a bandpass filter of 30 KHz.
  2. An appropriate antenna. Turnstile or QFH/QHA.
  3. PC with soundcard and decoding software.

[1] n average scanner that covers the VHF wxsat band will do. To get good pictures you will have to broaden the scanner's passband filter to 30 kHz. This is done by replacing a ceramic filter with a capacitor next to the FM demodulator chip. Picture of this modification soon to come...The location of the demodulator chip for most radio models can be found at www.discriminator.nl The ceramic filter is roughly 1x1x1 cm, orange or black in color with markings "455" or "450" manufactured by Murata. REMOVE THIS FILTER and replace it with a 10nF capacitor between pins 3 and 5.
On MY UBC220XLT this filter says SFP450D. It could theoretically be replaced with another filter with wider bandwidth but I used a capacitor.
[2] After fiddling with the receiver I turned my attention to the antenna. A part which is often overlooked. The bad thing with discones and LEO satellite reception is that discones have a 'null' right overhead. So they give a relatively good signal strength when the satellite is at the horizon but bad signal when the satellite is right overhead. Apart from this the polarization of most satellites is RHCP or LHCP (right hand circular, versus leff hand circular). Therefore I constructed an RHCP antenna based on the instructions found on the web for an antenna cut specifically for 137 MHz. I used copper tubing which proved to be amazingly user friendly in bending.
[3] Connect the audio from the receiver to the soundcards LINE IN and you are ready to go. WxToImg is an amazing software which will convert the faxlike signal into a visible image. The results were magnificent. Signal strength was very good even at passes 15 degrees above the horizon.

Click for real-size! Above: NOAA17 night-pass at 19.48 UTC the 23 March 2008.

Click for real-size!

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