ULTRA-HIGH-FREQUENCY SYSTEMS

The ultra-high-frequency (UHF) band (300-MHz to 3-GHz) is used for line-of-sight (short-range) communications. The term "line of sight," as used in communications, means that both transmitting and receiving antennas must be within sight of each other and unaffected by the curvature of the Earth for proper communications operation.

The UHF band is also used for satellite communications. Although satellite communications are line of sight, the distance the signal travels is much greater than that of UHF surface communications, because the antennas remain in sight of each other.

As in the VHF section, the transmit and receive systems will be described separately. Figure 1-5 shows a basic block diagram of a UHF transmit system, which uses a transceiver.

^1. On the transmit side of the nonsecure voice system, the operator at a remote location talks into the handset. The handset is connected to the C-1138 Radio Set Control.

2. The C-1138 is connected to the transmitter transfer switchboard, where it is patched to the transmitter.

3. The operator at a remote location talks into the secure voice remote phone unit (RPU).

^4. The RPU is connected to the secure voice matrix. This is the tie point for connecting more than one RPU. The output of the matrix is

Figure 1-5.-Ultra-high-frequency transmit system.

connected to the secure voice equipment, which encrypts the information received.

5. The output of the secure voice equipment is connected to the transmitter transfer switchboard.

6. The transmitter transfer switchboard is used to connect numerous RPUs to any number of transmitters.

7. The output of the patch panel is connected to the transmitter side of the transceiver, which, in turn, is connected to an antenna coupler.

Figure 1-6 shows a basic diagram of a UHF receive system. We will next follow the UHF signal path through the receive side of the system.

1. The received signal is picked up by the antenna and connected to the receiver side of the transceiver through the antenna coupler.

2. The output of the receiver is connected to the receiver transfer switchboard. From here, it can be connected to either the nonsecure or the secure voice systems, depending upon the mode of transmission.

3. When a nonsecure signal is received, the output of the receiver transfer switchboard can be connected to the radio set control or a speaker amplifier, or both, depending on the preference of the user.

4. The output of the radio set control is connected to a handset, whereas the output of the speaker amplifier is connected to a speaker.

5. If a secure voice transmission is received, the output of the receiver transfer switchboard is connected to the secure voice equipment, where it is decrypted.

6. The secure voice equipment output is connected to the secure voice matrix. The secure voice matrix performs the same function as the matrix on the transmit system.

7. The secure voice matrix output is connected to the secure remote phone unit. Here, the signal is converted back to its original form.