| ADC | - | An Analog to Digital Converter, also known as an “A/D”, or “A-to-D” converter. A device that samples an analog waveform, and converts it into a series of numbers representing the amplitude of the signal at the time of sampling. The input section of a computer "Sound Card" is a common use of ADC's. |
| AMSAT | - | The official acronym for the Radio Amateur Satellite Corporation. |
| APRS | - | An acronym for the Automatic Position Reporting System, a system developed by Bob Bruninga, WB4APR, for tracking and digital communications with mobile GPS equipped stations with two-way radio. |
| AX.25 | - | The amateur radio implementation of the X.25 packet switching protocol. |
| AZ/EL Rotator | - | An antenna rotator that can position antennas in both the horizontal direction (azimuth) and tilt (elevation) so that the antenna may be pointed directly at a satellite. May be computer or manually controlled. |
| Acquisition of Signal (AOS) | - | The time or location where signals from a satellite are capable of being received. |
| Amplitude Modulation (AM) | - | A type of modulation in which the amplitude (magnitude) of the carrier frequency is varied to convey the desired information content. An AM signal consists of the carrier wave, and two sidebands, one above, and one below, the carrier frequency |
| Antenna | - | A component in a radio system used for transmitting and receiving radio waves. Also called an "Aerial". |
| Antennae | - | Sometimes used (incorrectly) as plural for antenna. Correct usage is for insects and other biological entities. |
| Anti-fuse | - | A PROM programming technology that creates permanent links between elements to store information. Standard PROM programming opens the fuses to break the links between elements. |
| Aperture | - | The cross sectional area of an antenna. Also called "Capture Area". |
| Apogee | - | The point in an objects orbit where the object is furthest from the surface of the earth. |
| Attenuation | - | The process, intentional or unintentional, of decreasing the magnitude of a signal. |
| Automatic Gain Control (AGC) | - | A circuit which automatically controls the gain of a receiver so that the output signal level is virtually constant. |
| Automatic Level Control (ALC) | - | A circuit which automatically controls the gain of a transmitter so that the output signal level is virtually constant.
|
| Azimuth | - | The horizontal angle of rotation that an antenna must be rotated through to point to a location.
|