Applications

2-8 the receiver during the demodulation process. All rf energy appearing at the transmitter output is concentrated in the sideband energy as "talk power." After the carrier is eliminated, the upper and lower sidebands remain. If one of the two sidebands is filtered out before it reaches the power amplifier stage of the transmitter, the same intelligence can be transmitted on the remaining sideband. All power is then transmitted in one sideband, instead of being divided between the carrier and both sidebands, as it is in conventional AM. This provision gives you an increase in power for the wanted sideband. You should note in figure 2-8 that the bandwidth required for the ssb suppressed carrier, view B, is approximately half that needed for conventional AM, view A. This enables us to place more signals in a smaller portion of the frequency spectrum and permits a narrower receiver bandpass. Figure 2-8.—Comparison of bandwidths of conventional AM and ssb voice channels. Applications Single-sideband transmission is the most common communications mode used today. Some of the ssb applications used in naval communications are described for you in the following paragraphs. SSB VOICE CIRCUITS.—The high command (HICOM) network uses ssb as a means of communications between fleet commanders; and fleet commanders use it for communications between their subordinates and adjacent commands. Ssb is generally used whenever special voice communications circuits are necessary between shore activities or between ships and shore activities because it is less susceptible to atmospheric interference than amplitude modulation. SSB TELETYPEWRITER CIRCUITS.—With few exceptions, you will find ssb used on all long- haul (great distance) teletypewriter circuits, which includes ship-to-shore. Most of these systems are covered circuits; that is, an electronic cryptographic device on both ends of the circuit automatically encrypts and decrypts message traffic. These devices are used on point-to-point, ship-to-shore, ship-to- ship, and broadcast circuits.