ICF Interfaces

TM 11-5820-803-12

2-9.

ICF Interfaces

than 30 dB power loss at 5 MHz (regardless of the actual

data rate). The cable loss for installation must be

a. General.

The PSK modem is capable of

determined from the cable manufacturer's data and the

interfacing with the digital user over a line-of-sight (LOS)

cable length. For example, assume that RG-217/U cable

microwave link (fig. 2-12) or a shielded cable (fig. 2-13)

is being considered for a 10,000-foot installation. The

using an Interconnect Facility (ICF) modem located at

cable loss characteristic, in dB/100 feet, for RG-217/U

the digital user site. Both the PSK and ICF modems

cable (unbalanced type cable) is shown in figure 2-14.

contain identical LOS/cable driver circuits and LOS/cable

From figure 2-14, it can be seen that cable loss

receiver and decoder circuits. These circuits provide the

characteristics (a) at 5 MHz is 0.28 dB/100 feet

appropriate interface levels and code conversion to and

Therefore, for a cable length (L) of 10,000 feet of RG-

from the digital user's format to make the interface signal

217/U, the total cable loss can be determined from the

compatible with either transmission system

relationship:

b. Cable Installation.

cable loss = (al) ÷ 100.

(1) Cable selection. The cable selected for

cable loss = (0.28 x 10,000) ÷ 100 = 28 dB.

data transmission should normally provide no more

Since the cable loss in the example given above is less

than 30 dB, that length of RG-217/U would be usable

Figure 2-12. ICF/PSK modem configuration via line-of- sight (LOS) microwave terminal.

Figure 2-13. ICF/PSK modem configuration via shielded RF cable.

2-13