text: Chapter 6
  FUNDAMENTALS
  6-15. The team RTO transmits important information over the HF radio system. He continually adjusts
  it to keep up with changing conditions and missions. Successful HF communications depends on his
  knowledge; the type of emission (voice or data); the transmitter power output; selection of the best possible
  antenna and antenna site; proper antenna construction; propagated frequencies; terrain and weather; and
  atmospheric conditions. The variable over which he has the most control is antennas. To help eliminate
  skip zones, the RTO can achieve the NVIS effect with any HF-friendly antenna. This lets him establish
  communications with the COB or AOB. Extensive training of team members on HF radio systems and
  antenna construction is essential to mission success (TC 9-64, FM 6-02.74).
  BEYOND-LINE-OF-SIGHT EQUIPMENT
  6-16. In addition to communicating with many other types of digital and analog equipment, the LRSU
  also requires equipment that can communicate beyond line of sight (BLOS). Tactical VHF radios like the
  SINCGARS, are LOS only. The LRSU must be experts in the use of HF and TACSAT systems. Only HF
  allows long-range communications without the use of terrestrial or satellite relays. The LRSU can send
  either secure voice or data over HF.
  SPECIALIZED RADIO MODEM
  6-17. The ALE controller (modem) automatically controls a HF receiver and transmitter. This allows
  the radio to establish the best possible link with one or more HF radio stations. Each ALE controller
  (radiotelephone) can be embedded (internal) or external to modern HF radio equipment. It works on the
  principles of LQA and--
  • Has in memory a predetermined set of frequencies, each properly propagated for conditions.
  • Continuously scans its memory channels, typically about two channels per second.
  • Has call signs programmed in, including own (SELF) and network's.
  -- Network (NET) call signs.
  -- Group (GROUP) call signs.
  -- Individual (IND) call signs.
  • Transmits LQA, each of which sounds the programmed frequencies to find the one with the
  best link quality factors on a regular or automated schedule or when initiated by the operator.
  • In a listening mode, logs each station's call sign and ranks the station's associated frequencies
  and channels based on the quality of the link.
  • When someone at the station wants to place a call, tries to link to the outstation using the data
  collected during ALE and sounding activities. In the absence of this data, seeks the station and
  tries to link a logical circuit between two users on a network with all channels working. When
  the receiving station hears its address, the ALE controllers stop scanning channels and remain
  at that frequency. Each station notifies users that it has found the other station and is checking
  to confirm communications compatibility. This is called a "handshake." Once the handshake is
  complete, each station notifies its users that it is ready for traffic. Figure 6-1 shows
  communications between two stations during the "handshake" and LQA.