Automatic picture transmission

It was introduced in the 1960s and over four decades has provided image data to relatively low-cost user stations at locations in most countries of the world.

The synchronization information, transmitted at the start of each video channel, allows the receiving software to align its sampling with the baud rate of the signal, which can vary slightly over time.

The telemetry section is composed of sixteen blocks, each 8 lines long, which are used as reference values to decode the image channels.

An APT signal is continuously broadcast, with reception beginning at the start of the next line when the receiver is within radio range.

Most older scanners (police and fire type receivers) are the standard 15 kHz bandwidth which were designed to support voice transmissions.

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.

APT images from weather satellites can be received with a right-hand circular polarized, 137 MHz antenna.

Nowadays, with the advent of personal computers, all that is required is dedicated software such as WXtoIMG (many of which offer "free" versions [1]) and a sound card.

The sound card acquires and digitizes the slow scan video (in the audible range) coming from the speaker, phones, or line-out of the receiver, and then the software will process the various visible and infrared channels of the AVHRR sensor.

NOAA-19, called NOAA-N' prior to its launch on 6 February 2009, is the last satellite to carry an APT system.

[2] The MetOp program, a collaboration between NOAA and EUMETSAT, has switched to Low Rate Picture Transmission (LRPT) for its new polar-orbit satellites.