APT Automatic Picture Transmission

Click here to learn about my Quadrifilar antenna.

With a special antenna, receiver and software, I receive Automatic Picture Transmission (APT) images direct from Polar-obiting Operational Environmental Satellites (POES) operated by NOAA at my home in Gold Canyon, Arizona. APT is the low resolution mode sent down from these weather satellites. They also send a higher resolution mode known as High Resolution Picture Transmission (HRPT) on microwave frequencies. I myself do not receive the HRPT signals, only the APT transmissions. The APT signals are transmitted on VHF frequencies between 137 and 138 mhz. The continuous broadcasts are around 5-watts, thus somewhat weak requiring a high-gain antenna for reception. Antennas such as a specially designed Turnstyle or Quadrifilar work best. Although the Quadrifilar antenna does outperform the Turnstyle antenna.

Explanation of my weather satellite receiving station.

Signals transmitted from passing NOAA weather satellites are received by my specially designed Quadrifilar antenna. The antenna is mounted on the roof of the house and connected with coax feedline to a Hamtronics R-139 receiver. Demodulated audio from the R-139 receiver is connected to the line-in of my computer's sound card. Using a program called WXtoImg, audio from the sound card is saved on the computer's hard drive as a wave file. The software then processes the wave file and converts it to an image. The image is then overlaid with a map and text, then uploaded to the website.

My Quadrifilar antenna design is based on the Tall Narrow Quadrifilar Helix Antenna design by Steve Blackmore. My radio receiver is the R139 Weather Fax Receiver made and sold by Hamtronics. You can see some pictures of my current antenna, with some design notes here.