TM 1-1520-238-10 Change 2 3-17 3.7.4 Warning Tones. a. A steady warning tone will be heard in the headset when the AJ mode is selected and TOD, or a valid WOD, has not been entered. b. A pulsating warning tone will be heard in the head- set when an invalid operating net is selected. 3.7.5 Conference Capability. NOTE Conference communication is not possible when operating in the secure voice mode. In the AJ mode, the radio can receive and process two si- multaneous transmissions on the same net. This confer- ence capability is available by selecting 00, 50, or 75 with frequency selector 5 and then operating in the AJ mode. Conferencing is not possible when the net number ends in 25. In a conference net, the second transmitting radio will au- tomatically shift its transmission frequency by 25 kHz when it monitors a transmission on the primary net fre- quency. The wide band receiver will read both transmis- sions without the interference normally associated with two radios transmitting on the same frequency simulta- neously. Three simultaneous transmission will result in garbled reception. 3.7.6 Guard Operation. NOTE If the guard frequency is being jammed with the mode selector switch in the BOTH posi- tion and the radio in the AJ or normal mode, set the mode selector switch to MAIN. The guard receiver is not affected by AJ mode operation. The guard frequency may be monitored regardless of mode as long as the mode selector switch is set to BOTH. The BOTH position turns on the main transceiver and guard receiver. The guard receiver will remain tuned to 243.000 MHz regardless of manual or preset frequencies selected. When the function selector switch is set to GUARD, the AJ mode is removed, the guard receiver is turned off and the main transceiver is set at 243.00 MHz, making it possible to transmit and receive on the guard frequency. 3.7.7 Secure Communication. The HQ radio has a se- cure (cipher) communication capability. In either the nor- mal or AJ mode, the radio can perform cipher mode op- eration. The effectiveness of communications in the AJ cipher mode depends on the frequency hop rate. It is rec- ommended that the slowest hop rate (channel 20 WOD set at 00) be used during AJ cipher mode operation. 3.7.8 Normal Mode Operating Procedures. a. Loading Preset Channels. 1. Mode selector switch – MAIN or BOTH. 2. Frequency selectors – Select frequency to be set in memory. 3. Function selector switch – PRESET. NOTE For HQ radios, do not select channel 20. 4. Preset channel selector – Set to channel to be loaded. 5. Open the switching unit cover. 6. PRESET button – Press. The frequency is now loaded into memory. 7. Repeat steps 2, 3, 4 and 6 to complete preset- ting channels. 8. Close and latch switching unit cover. b. Transmit/Receive (MAIN) Operating Proce- dures. 1. Mode selector switch – MAIN. 2. Function selector switch – MANUAL. 3. To manually select a frequency, set the five MHz selector switches until desired frequency is dis- played in indicator windows. 4. To select a preset channel, rotate preset chan- nel selector until desired channel is displayed in CHAN indicator window. c. Transmit/Receive/Guard Monitor Operating Procedures. 1. Mode selector switch – BOTH. NOTE If reception on the selected frequency inter- feres with guard frequency reception, de- tune the radio set by selecting an open fre- quency or set function selector switch to GUARD.