Signals, Emissions, and Modulation: Analysis and Emission Designators
Describing a signal
A modulated signal consists of a carrier and sidebands. In amplitude modulation with modulation index m, total power = carrier power x (1 + m squared / 2); each sideband carries m squared / 4 of the carrier power. At 100 percent modulation the two sidebands together equal half the carrier power. Single sideband suppresses the carrier and one sideband, so peak envelope power and two-tone tests replace carrier-power measurements, and SSB amplifiers must be linear.
Angle modulation
FM and PM vary frequency or phase. Deviation (delta f) and the highest modulating frequency (f_m) set bandwidth by Carson's rule: BW is approximately 2 x (delta f + f_m). Narrowband FM with 5 kHz deviation and 3 kHz audio fits in about 16 kHz.
Emission designators
Each emission is described by a code: bandwidth (three digits plus a letter, where K = kHz, M = MHz, H = 0.1) followed by three symbols. First symbol = main-carrier modulation (A = AM double sideband, F = FM, G = PM, J = SSB suppressed carrier, P = pulse). Second = nature of the modulating signal (1 = single digital channel, 3 = single analog channel). Third = information type (E = telephony, D = data, A = aural telegraphy, N = none).
Traps
Do not confuse deviation with occupied bandwidth, and do not total sidebands while forgetting the carrier. Recognize 16K0F3E as 16 kHz FM voice, 2K80J3E as 2.8 kHz SSB voice, and 6K00A3E as 6 kHz AM voice. Occupied bandwidth is measured where 99 percent of mean power lies.
Rule of thumb: at 100 percent AM modulation each sideband holds one quarter of carrier power.