Overview
Voice over radio channels (radiotelephony or just "phone") is probably the most popular form of Amateur Radio. A number of modulation modes are available to support voice work.
- AM (Amplitude Modulation - double sideband, full carrier) is the oldest form of voice modulation. A CW carrier signal is controlled (modulated) by an audio voltage, so that the amplitude of the radio carrier ranges from zero (at negative audio peaks) to 200% (at positive audio peaks). Generation and reception of traditional AM can be done with relatively simple circuits, and it is still in use by a small, but hardy group of amateurs. (See the AM Phone page.) Nevertheless, most ham voice activity on HF has moved to SSB (see below).
- Digital Voice is a new technique built around analog to digital converters and codecs that sample a voice signal, compress it, and transmit it as a bit stream. Like other digital media, digital voice offers interference free communications if the radio signal is strong enough to overcome the general noise and interference level.
- FM (Frequency Modulation) is the voice mode of choice for local VHF / UHF operations, fixed or mobile, simplex or repeater based. It offers good performance with simple equipment requirements. The audio signal controls (modulates) the frequency of the transmitter over a small range.
- SSB ("sideband", Single Sideband Suppressed Carrier) is the descendant of traditional AM. Compared to AM, SSB requires less than half the bandwidth and it offers much more "talk power", since the unnecessary carrier and second sideband are not transmitted. SSB requires more frequency stability and somewhat more complex circuitry than AM, but essentially all mainstream amateur gear for the HF bands now supports SSB voice.
