Beyond line-of-sight communications

Many areas of the country, including Alaska, still require beyond-line-of-sight communications for public safety and other government agency use. While many managers consider the use of portable satellite terminals (P-phones) as the complete answer to their needs, many others have once more discovered the advantages of high-frequency, single-sideband (HFSSB) radios for their communications needs. I will cover ease of use, cost, portability, minimum equipment requirements as well as current government standards and programs for automatic link establishment (ALE) systems and SHAREs, a frequency sharing program. Relevant operating technical standards are FED-STD-1045 through 1052.

Unless you work with HFSSB systems, you may not be aware of the number of systems in use or the applications for public safety. Much of the desire for agencies to move away from this type of communications system was the perceived complexity of operation, lack of reliable paths and assumed need for
massive antenna systems. However, things have changed in the last few years.

Modern automatic link establishment (ALE) radio systems convert the operation of the system from a complex endeavor to one as simple as using the telephone. ALE, under Federal Standard FED-STD-1045A (see the standard at www.its.bldrdoc.gov/fs-1045a/45-scop.htm) allows similar equipment to "meet" on the best frequency for communication—all with no operator
intervention. Gone are the days of knob twiddling and flipping numerous switches. Motorola makes a line of medium-powered portable radios (MICOM-2E) that communicate with each other to maintain a telephone-like circuit. They also offer digital interfaces for email, selcal, priority and guard channels. You may have seen some of these as part of some agencies’ Y2K preparations.

The cost of HFSSB radio is limited to the initial installation, training and normal maintenance found on any communications systems. While satellite radiotelephones offer high-quality circuits around the clock, they can also cost close to $3 a minute (or more), and you may have trouble in finding transponder space as an itinerant user. This becomes even more of a problem in a wide-area disaster where communications are critical for public safety. HFSSB, on the other hand, carries no such toll in most areas of the world. If you are willing to use non-ALE equipment, the cost is even lower.

The size of HFSSB equipment has diminished considerably in the last several years. Dash-mount radio systems are available from several vendors and come with remote autotune antenna systems that can be mounted in several types of mounts. Along with size reduction, the use of direct, digital synthesizers means that drift is no longer really an operational factor, allowing the use of outboard digital communications systems for computer-to-computer or text-based communications. Drift rates of less than three parts per million are common, and some units offer even tighter specs for frequency control. Operating frequencies are stored in memory, often with hundreds of "channels" available in even the smallest of rigs.

What does it take to operate an HFSSB system? As they say, "Your mileage may vary." The most common system type found in public safety is the example here in Alaska, a fixed base station with a larger antenna array and small portable dc-powered units used in the field. In the case of Alaska, a mix of commercial Motorola and Harris units are deployed with modified (approved) Kenwood amateur service radio sets. The amateur radio population in Alaska has a long history of public safety support from territorial days to the "big one" (earthquake) in 1964, so the state is prepared with both types.

A common emergency field system is supplied with an HF set, antenna, cable ac and dc power supplies, appropriate VHF or UHF public service hand-held radios and if the situation calls for it, a citizens band radio set. This field set would communicate back to a central site equipped with commercial ALE gear or an amateur radio operator (several are on staff at the state EOC) as the situation develops. The central site is set with both large log periodic and simple dipole antenna arrays. This type of arrangement permits maximum flexibility and minimum cost to operations. Many other states have similar situations.

Federal standards are aimed more at protocols rather than simple technical specifications. The standards of most interest to public service agencies are:

©FED-STD-1046 HF Radio Automatic Networking—This includes polling, connectivity exchange and enhanced LQA.

©FED-STD-1047 HF Radio Automatic Store-and-Forward—This includes message store-and-forward and network coordination and management.

©FED-STD-1048 HF Radio Automatic Networking to Multiple-Media—This includes features that interface with other types of communications systems.

©FED-STD-1049 HF Radio Automatic Operation in Stressed Environments—This includes linking protection that relates to link authentication, address protection, antispoofing, encryption and anti-interference.

©FED-STD-1050 HF Radio Baseline Parameters—This defines the minimum performance requirements to enable the radio to support automated operations.

©FED-STD-1051 HF Radio System Controller Interface—This defines the functional interfaces both for radio control and for higher level functions.

©FED-STD-1052 HF Radio Modems—This includes high-performance
modems, minimum mandatory interoperability modes and an automatic
error-free message delivery system.

The National Institute of Standards and Technology (NIST) offers support for ALE maintenance by offering recorded tones to use for off-the-air testing and adjustment. Use the Internet to obtain the full text of these standards. A comprehensive review of these standards prior to issuing a request for bid or request for proposal may save funds and ensure that equipment purchased will be compatible with the maximum numbers of public safety users.

Public safety users may find themselves sharing a pool of frequencies—which is not all bad. Your application and location will determine what frequencies you may use. SHAREs may be something your agency would want to participate in. According to representatives of the program, "The purpose of SHAREs is to provide a single, interagency emergency message handling system by bringing together existing HF radio resources of federal and federally affiliated organizations when normal communications are destroyed or unavailable for the transmission of national security and emergency preparedness information. SHAREs further implements Executive Order No. 12472, Assignment of National Security and Emergency Preparedness Telecommunications Functions, dated April 3, 1984." For more see www.ncs.gov/n3/shares/overview.htm. It may not be for you , but it is worth looking into if your group is focused on disaster response, recovery or restoration.

HFSSB radio systems may not be for everyone—but they provide a low-cost alternative to dependence on satellite-based systems that can be both costly and difficult to gain access to in emergency situations. Modern systems are small, lightweight and automatic, and they provide messaging when alternatives might not exist. Many states currently count on HFSSB systems for a variety of public safety communications. n

 

To learn more visit:
www.motorola.com/LMPS/RNSG/ mobiles/micom/
wsp3.wspice.com/~bfreeman/comm/ hf_radio.htm
www.rfcomm.harris.com/defense- comm/ssradios/