| 1. | A-index | An index of the conditions of the Earth |
| 2. | absorption | The reduction in a radio signal amplitude due to refraction in the ionosphere. |
| 3. | AC | Alternating Current |
| 4. | AD | Analog-to-Digital |
| 5. | AF | Audio Frequency 20 to 20,000 hertz, human hearing range. Also Africa |
| 6. | AFC | Automatic frequency control |
| 7. | AFSK | Automatic frequency shift keying |
| 8. | ALC | Automatic level control. A feedback voltage in the transmitter's output amplifier used to prevent amplifier overload. |
| 9. | Alligator | A repeater that transmits further than it can receive, big mouth, small ears! |
| 10. | AM | Amplitude Modulation See URL: Modulation Modes |
| 11. | AMATEUR | a person licensed to operate in the amateur bands |
| 12. | amateur radio | A non-commericial radio service as set by a recognized cognizant government agency. In the USA, amateur radio is defined under part 97 of the FCC Rules and Regs - See URL: Part 97 |
| 13. | AMSAT | Radio Amateur Satellite Corporation - See URL: AMSAT |
| 14. | AMTOR | Amateur Teleprinter Over Radio. A version of RTTY. - See URL: AMTOR Also used commercially as SITOR (Simplex Teleprinter Over Radio). |
| 15. | ANARC | Association of North American Radio Clubs |
| 16. | antenna farm | a location which has numerous antennas |
| 17. | APRS | Automatic Packet Position Reporting System - See URL: APRS |
| 18. | ARA | Amateur Radio Association |
| 19. | ARC | Amateur Radio Club. Military Designation for Avionics (Aviation Radio Composite) |
| 20. | ARES | Amateur Radio Emergency Service - See URL: ARES |
