NOAA Weather satellites
Me and a friend started to talk about SDR (Software Defined Radio) and GNURadio [1], which reminds me of a old project I did for many years ago - reading out images from NOAA weather satellites using SDR, a QFH antenna and GNU Radio!
I found some old pictures, but unfortunately, I do not remember the details as it was almost ten years ago. But I do know that we were using a HackRF [3] to catch the radio signals.
The satellites
There are a bunch of satellites out there and a lot of those are used for weather information. Currently there are three NOAA satellites available transmitting APT weather pictures, those are
| Satellite | Frequency (MHz) |
|---|---|
| NOAA-15 | 137.620 |
| NOAA-18 | 137.9125 |
| NOAA-19 | 137.100 |
NOAA is not the only one who has weather satellites in orbin, there is also, for examle, the Russion METEOR M N2 satellites.
You may track the satellites in orbit live on this site [4].
The antenna
The radio signals radiated from the satellites are circular polarized waves which is almost always the case for space applications. This is because of that a linear polarized radio waves requires a fixed relative orientation of the antennas, which is simply not possible in space.
The satellites operaties in the frequency range of 137 MHz to 138MHz and are transmitting a RHCP (Right Hand Circular Polarized) signal.
So the antenna I built was a Quadrifilar Helix Antenna trimmed for 137.5MHz to be in the center of NOAA-15, NOAA-18 and NOAA-19. If I recall correct, I think the satellite we got the images from was NOAA-19.
I found this document [2] (local copy here: How-to-build-a-QFH), on how to build a qaudrifilar helix antenna for the same purpose. The document was originally written by Tin Hat Ranch and revided by Carl Reinemann.
It does cover everything you need to build your own antenna, but it does not have to be that complicated. I used some drain pipe and coax cable to build mine.
Mounted on a ladder next to the garage:
The result
This was a cool project and I still have the antenna in my garage, so maybe I will try to fetch another picture some day.
To summarize: The weather in Svalbard was cloudy at 13:22 on December 25, 2015. The northwestern part of the Norwegian coast and the eastern part of Greenland had clear weather.
