TM 1-1520-238-10 3-27 3.10.3 Modes of Operation. a. ECCM Mode. The ECCM mode provides a jam resistant capability by means of a (FH) technique that changes frequency many times a second. Automatic fre- quency changing in an apparently random manner pro- vides the jam resistance of the radio. This capability per- mits communications in radio jamming environments. For uninterrupted successful communications, radios must be time synchronized with each other and share a common net. (1) Time Synchronization. Time synchroniza- tion is provided by a clock inside the radio set. The opera- tion of the (FH) net is time dependent and the accuracy of time, as it is registered in each radio set on a common net, is of significant importance. A relative standard or master must be established to prevent gradual time creepage during normal communications. One radio set will be des- ignated as master. The time difference will be accommo- dated in the other radios, not the master radio. The net control station, or master, is designated as the time stan- dard for all radio sets in the net. (2) Loading ECCM Parameters. To use the ECCM function, TRANSEC variables and hopsets or lock- outs are loaded into the transceiver by an external fill de- vice connected to the FILL connector. (3) Signalling an ECCM Radio. In a typical ECCM signalling operation, an operator with a non-ECCM radio set attempting a contact within an ECCM net places the PRESET switch to CUE. The ECCM radio display indi- cates CUE for 7 seconds and the ECCM radio operator hears a tone in his headset for 2 seconds each time the non-ECCM radio is keyed. The non-ECCM radio must be keyed for at least 4 seconds to insure reception by the ECCM radio. The ECCM radio is then switched to the single channel CUE frequency or some other predeter- mined frequency to establish contact. b. Other Operational Modes. Depending on the settings of the operational controls, the radio set can be used for the following modes of operation: (1) Two way clear voice (SC). (2) Two way secure voice with TSEC/KY-58 installed (SC). (3) Two way frequency hopping voice (FH or FH- M). (4) Two way frequency hopping secure voice with TSEC/KY-58 installed (FH or FH-M). 3.10.4 Operating Procedures. a. Manually Entering Frequency. When using the nine digits on the keyboard, entry of information is normal- ly displayed digit-by-digit left to right on the display. Op- eration of the transceiver is altered only after complete, valid data is registered on the display and the Sto ENT button pressed within the 7 second time-out period. Illegal entries will not register on the display. Incomplete entries will not be accepted when the Sto ENT button is pressed. Acceptance of valid data is signaled by a momentary blink of the display when the Sto ENT button is pressed. At this time, the transceiver acts upon the entry. Partial or erroneous data can be erased at any time by pressing the CLR button, at which time the last readout will be cleared. 1. FUNCTION switch – SQ ON or SQ OFF, as de- sired. 2. MODE switch – SC. 3. PRESET switch – MAN. 4. FREQ button – Press. Frequency is displayed. 5. CLR button – Press. Display shows all bottom dashes. 6. Keyboard – Enter 5 digits for frequency. 7. Sto ENT button – Press. Display blinks momen- tarily. b. Loading Preset Channels. Seven preset chan- nels are available (PRESET positions 1 through 6 and CUE). These channels select discrete frequencies in non- ECCM modes and provide an analogous function in the (FH) ECCM mode. The function of the PRESET switch is two-fold. In a normal single-channel mode (MODE switch set to SC), either manual or preset frequencies are se- lected. In an ECCM frequency hopping mode (MODE switch set to FH or FH-M), nets are selected according to predetermined preloaded data. When a (FH) net is se- lected, the display will indicate FH followed by the corre- sponding valid (FH) data number. The CUE frequency can serve as a seventh preset