The Satellites. Full details of the satellites can be found at the NOAA web site:

The polar orbitting satellites tracked here at Wokingham are in sun-synchronous orbits, at about 800 km above mean sea level. Each complete orbit takes about 100 minutes, the satellite thus covering the ground at a speed of 7.5 km per second. Currently (begining of 2003) I receive data from three satellites, noaa12, noaa16 and noaa17. At present noaa12 is northbound in the mid-afternoon, noaa16 is northbound near midday, and noaa17 is southbound in the late morning. The northbound passes of noaa17 are during the evening, and the southbound passes of noaa12 and noaa16 are during the night. Constraints of my time only allow me generally to take the daytime passes at present. Each satellite is visible above the horizon for two or three passes during both its ascending and descending nodes. Although data is usable from elevations as low as about 3 degrees above the horizon, provided the line of sight is clear of obstruction, I currently do not process passes whose maximum elevation is below 20 degrees.

Hardware. The satellite receiver consists of an aluminium 65-cm dish antena with a AHF-1700 active helical feed giving over 55 dB gain. The dish is mounted on a G-5400 rotator assembly atop a short aluminium mast attached to the side of the house. The HRPT receiver is mounted on a PC card and links to a 16 bit data card. Tracking software activates a rotator interface unit, which provides the up/down, left/right signal to the elevation/azimuth controller, connected to the rotator controller unit.

The PC cards are mounted in an 'old' 486 PC running at appx. 100 MHz (upgraded to 150 MHz, April 2004). This is sufficient for receiving the satellite image files, while continuously calculating the exact position of the satellite and controlling the dish pointing hardware. The satellite is above the horizon for about 15 minutes during each pass, and in this time about 4500 to 5000 lines of data are received, a rate of about 5 lines per second. Each line consists of about 12 kb of data, so that the entire pass generates files between 50 and 60 Mb in size.