matching the intensity of one of the wedges one through six. Video channel A typically matches either wedge two or three, channel B matches wedge four. The first fourteen blocks should be identical for both channels. The sixteen telemetry blocks repeat every 128 lines, and these 128 lines are referred to as a frame. Broadcast signal The signal itself is a 256-level amplitude modulated 2400Hz subcarrier, which is then frequency modulated onto the 137 MHz-band RF carrier. Maximum subcarrier modulation is 87% (±5%), and overall RF bandwidth is 34 kHz. On NOAA POES vehicles, the signal is broadcast at approximately 37dBm (5 watts) effective radiated power. Receiving images An APT signal is continuously broadcast, with reception beginning at the start of the next line when the receiver is within radio range. Images can be received in real-time by relatively unsophisticated, inexpensive receivers during the time the satellite is within radio range, which typically lasts 8 to 15 minutes. there were almost 5,000 APT receiving stations registered with the World Meteorological Organization (WMO). It is unclear what percent of the total user-base this represents, since registration is not a requirement, and was only available after 1996. Radio receiver The bandwidth required to receive APT transmissions is approximately 34 kHz. Most older scanners (police and fire type receivers) are the standard 15 kHz bandwidth which were designed to support voice transmissions. Newer VHF general coverage receivers are equipped with multiple IF bandpasses; some are, but not limited to: 6 kHz, 15 kHz 50 kHz & 230 kHz(broadcast FM). Use of a receiver with too narrow a bandwidth will produce pictures that are saturated in the blacks and whites, as well as possible inversion. Too wide, and the noise floor of the receiver will be too high to acquire a good picture. For the amateur enthusiast, a computer controller receiver is the best option to allow the software to automatically tune and set the required modes for proper reception. There are also dedicated APT receivers made specifically for computer control and APT reception. Specifically, ICOM PCR1000, PCR1500 & PCR2500 will produce excellent results. Searching on the web for "NOAA APT (RECEPTION or RECEIVER)" will produce a wealth of information on receivers, software, and antennas. Antenna APT images from weather satellites can be received with a right-hand circular polarized, 137 MHz antenna. Normally, there is no need to have the antenna follow the satellite