FS-1052: General Requirements

4.1 General system description. Data modulators-demodulators (modems) are employed in both automatic and manual HF radio systems. Data modems employ a variety of techniques for converting digital signals into quasi-analog signals for transmission over analog channels. This section covers general requirements for data modems operating over HF radio channels. Figure 1 shows standard interfaces in a typical system.

4.2 Common parameters. All data modems shall comply with the applicable requirements of pars. 4.2.1 through 4.2.6.

4.2.1 User data rates. The modem shall support user data rates, expressed in bits per second (b/s), of 75, 150, 300, 600, 1200, 2400, and 4800. Except where specified otherwise, signaling rates shall not deviate from the nominal values by more than ±0.01%.

4.2.2 Logic and signaling sense for binary signals. For data and timing circuits, the signal voltage with respect to signal ground shall be negative to represent the MARK condition and positive to represent the SPACE condition. The significant conditions and other logic and signal states shown in Table I shall apply to telegraph and data transmission. An alternative capability shall be provided to interface with equipment that accepts positive MARK and negative SPACE signals.

4.2.3 Digital interface characteristics. The electrical characteristics of the digital interface at the modulator input and the demodulator output shall be in accordance with the applicable requirements of FED-STD-1020 and FED-STD-1030.

Figure 1. Typical interface between data terminal equipment and data circuit-terminating

equipment

4.2.4 Terminal impedance for quasi-analog signals. (This interface applies to external modem implementations only.) For modems used with radio equipment of single-channel radio subsystems, the terminal impedance at the modulator output shall be 600 ohms, ±10%, balanced to ground. A 150 ohm terminal impedance, unbalanced to ground, is optional. The terminal impedance at the demodulator input shall be 600 ohms, ±10%, balanced to ground. The electrical symmetry shall be sufficient to suppress longitudinal currents to a level which is at least 40 dB below reference level (-40 dBmØ).

4.2.5 Quasi-analog signal levels. Standards for the quasi-analog signal levels of modulators and demodulators are documented in FED-STD-1045A.

4.2.6 Clock equipment, control, and timing. Clock equipment, control, and timing for modems shall be in accordance with the applicable requirements in MIL-STD-188-115. All data modems shall have the capability to accept external timing signals (optional for frequency-shift keying (FSK) modems).

4.3 General design requirements.

4.3.1 Federal maritime interoperability requirements (optional).

Ship-to-ship and shore-to-ship HF radio teletypewriter system (RATT) operation shall be in accordance with the requirements of FED-STD-1035.

4.3.2 International interoperability requirements.

4.3.2.1 Shore-to-ship broadcast systems (optional). For interoperation with North Atlantic Treaty Organization (NATO) member nations, the electrical characteristics of data modems employed in shore-to-ship broadcast systems shall be in accordance with the applicable requirements of NATO Standardization Agreement (STANAG) 5031.

4.3.2.2 Maritime air communications systems (optional). For interoperation with NATO member nations, the electrical characteristics of data modems employed in maritime air communication systems shall be in accordance with the applicable requirements of STANAG 5035.

4.3.2.3 Radio teletypewriter systems (optional). For interoperation among American, British, Canadian, Australian (ABCA) armies, the electrical characteristics of data modems employed in HF RATT operations shall comply with the applicable requirements of Quadripartite Standardization Agreement (QSTAG)-303.

NOTE: The applicable characteristics of data modems standardized in this document comply with STANAG 5031, STANAG 5035, and QSTAG-303.