The APT signals are polarized by a process called Right Hand Circular Polarization or RHCP, and they require a right-hand polarized antenna to receive the signal without losing a significant part of the information being sent. Keep in mind that each row shows 10 times more frequencies than the previous row. The FCC allocates different frequencies to different public and private types of communications. The NOAA satellites make use of infrared and microwave imaging systems and they transmit imaging data to Earth in two systems, the Automatic Picture Transmissions (APT) and High Resolution Picture Transmissions (HRPT). Three NOAA Satellites, NOAA 15, NOAA 18, and NOAA 19 orbit the Earth from pole to pole while the Earth rotates beneath them, and as a result, each NOAA satellite passes clearly overhead between one and three times in a 24 hour period. This was pretty interesting for exploration, but my main goal was to receive images from the National Oceanographic and Atmospheric Administration’s (NOAA) Satellites. Using SDR# I was able to hear a lot from local FM radio stations, police/fire department communications, and local air traffic controller.
HOW TO CLEAR IMAGES FROM WXTOIMG DRIVERS
On the software side, I ran into some issues with Windows assigning the wrong drivers to the dongle, and I found the instructions on the blog’s quickstart guide to be very helpful. Basic hardware setup was pretty simple: plug it into a USB port and screw the antenna onto the SMA port. I specifically used the blog’s $26 kit, and I recommend it to those who are interested in starting with software-defined radio. Last November, I got a small RT元832U SDR USB dongle to experiment with receiving radio signals from my computer. I expect to tweak it throughout the next month and I hope to present it at Makerfaire Bay Area this May.
My antenna’s construction leaves something to be desired, and I suspect it to be the source of the wavy black lines that are prevalent in most of my images. I’ve found that the worst images have low pass altitudes, and are taken during times of low light, and I have yet to get a good MCIR image. Results have been pretty good: Most of the images received are poor since the Pi lacks high speed sampling power. I can’t make a wired connection without investing in a good MoCA network, so I’m looking into other solutions. There is one challenge I didn’t expect with this project, and that is that my internet connection is really poor in my garage. I edited this last script to also run a small python file that posts the images shortly after making them. These passes are then scheduled into the Pi’s task queue, and the last script is called by the queued events and record the audio and processes it into MCIR and default filtered images with a map overlay.
The Instructables guide makes good use of some scripts that are run automatically by the Pi’s cron table daily to check Predict for NOAA passes with over 20 degrees of altitude. I also installed Twython to enable the Raspberry Pi to interact with Twitter’s API through Python code. I set up the Raspberry Pi with Raspbian on a 32GB MicroSD card and loaded all the software as detailed on the Instructables guide: rtl-sdr, SoX, at, predict, and WXtoIMG. I ran an SMA cable from the coaxial strand of the helix into the inside of my garage and found that it did not interfere with the door and wiring through the walls would not be necessary. I laser-cut a small acrylic plate bolted my Raspberry Pi onto it before suspending it from the ceiling. I used a quadrifilar helical antenna that I built for 137MHz frequencies and I set it up on the roof of my garage. I’ve long enjoyed setting up and recording passing NOAA satellites, and when I saw this Instructables guide on making a Raspberry Pi into a weather satellite receiver, I knew it would be a great next step. My QFH on the roof wired to a Raspberry Pi indoors
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