A run-down of some of the wonderful modes Amateur Radio Operators are allowed to use.
- Single Side Band (SSB)
The most used of all modes. In a nutshell is "half" of a carrier wave on a given frequency.
Example: An AM transmission is made up of two identical modulating signals (Two SIDE Bands) on one carrier. A Single Side Band transmission utilizes only one of these signals. One "over" the carrier or one "under" the carrier.
Result: Either an Upper Side Band transmission or a Lower Side Band Transmission that takes up half the space and produces a much more efficient transmission since it only transmits the modulation of one of the two signals and not the constant carrier signal nor the other modulating signal.
Uses: Mostly used on HF bands (Below 50Mhz.) for voice and digital transmissions because of it's ability to travel longer distances with less power than other modes.
- Amplitude Modulation (AM)
One of the oldest forms of transmitting audio over a radio signal. Consists of a constant transmission "carrying" modulation.
Example: The difference between the highest point of an ocean wave down to the calmest point of the water is the "Amplitude" of that wave. Conversely, the difference between the lowest point of a trough in the ocean up to the calmest part of the water is the "Amplitude" of that trough. It is the same in a radio transmission where as the wave is that of the radio signal.
Result: An Amplitude Modulated signal consisting of a carrier signal and two identical "waves" of audio, one "over" the carrier and one "under" the carrier being transmitted at the same time. Makes for a less than efficient transmission but is also a much "easier" transmission to create requiring less processing than other modes.
Uses: Mostly used on HF bands (Below 50Mhz.) for voice transmissions for it's ability to travel fairly long distances with less power than an FM transmission.
- Frequency Modulation (FM)
A mode of transmission conveying high tonal quality at the expense of bandwidth (Uses much more.) and relative distance.
Example: The carrier frequency of an FM signal is directly proportional to that of the audio frequency on that signal. Compare to an AM transmission where the carrier frequency stays constant regardless of the audio frequency. Since higher radio frequencies have smaller wave lengths, this mode is typically used on VHF and higher bands, the higher the better in Amateur Radio use since our band allotment is relatively small in the HF spectrum.
Result: High quality audio, much less noise on the carrier but by its nature, a much larger amount of bandwidth is needed to convey the information.
Uses: Mostly used on VHF and UHF transmissions (Above 50Mhz.) such as on repeaters and local transmissions. Travels shorter distances than other modes but adds audio quality.
More to come - Stay Tuned for the Digital Modes!