Antennas for Emergency Communications
Amateurs have a long history of providing communications in emergencies. But antennas don’t change just because there is an emergency: the same principles still apply and the same designs work over the same paths with the same efficiency. Is there anything else to say about it?
Yes there is, based on the number of designs and commercial products that claim to be “perfect for emergency use” without apparently giving much thought to what that really means. Let’s touch on a few topics:
- Advance Planning
- Desired Characteristics for Emergency Antennas
- Antennas to Survive an Emergency
- Antennas to Put Up in an Emergency
- Improvised Antennas
This is an important step that some hams tend to skip. Probably the most important question is, “Who are you going to talk to?” Just being able to talk on your radio doesn’t mean that you can get a message through to someone who can respond to the emergency. (Do you know who that is?) Or, if you do get a message to the right person / agency, will your message contain all the required information and authorization that they need to respond?
Emergencies come in all sizes and types, from a traffic accident or injured hiker in the wilderness to a sinking ship, earthquakes, floods, hurricanes / typhoons, tornadoes, snow storms, volcanic eruptions, mud slides, wildfires, etc. And most areas have government or other agencies that are tasked with responding to different situations.
One problem, of course, is that ham radio is capable of spanning large distances. A call from a ship in distress, for example, can be picked up on a different continent, and then needs to be relayed to the closest rescue agency or other ships that may be in the vicinity, that may not be able to hear the initial call due to propagation. Even for a land-based emergency, if my call is answered by a ham in a different country, how will they know which county, state, or federal agency to call?
Generally, the most effective communications we can provide as hams is when we work with the responsible agencies and plan our response in advance. This includes plans for what frequencies and modes to use, stations to call, etc. In this approach, the individual hams do not originate emergency messages: instead, messages are generated by local officials, and ham radio is simply a backup means to transmit them when other official communications are disabled due to an emergency. With this planning, we can choose antennas most appropriate for those bands and the distances to be covered.
For example, the State of Oregon is roughly 650km by 500 km (400 miles by 300 miles). We are subject to potential events (including earthquakes and volcanic eruptions) that can affect much of that area at one time. Local emergency communications are mostly handled on VHF/UHF FM (including plans for when repeaters are not functional). HF NVIS is used for state-wide SSB nets. Winlink digital messaging can use several different HF bands over longer distances to link to stations outside an affected area. Each of those has different antenna requirements that we need to plan for. Without that advance planning, we may find that our antennas aren’t suitable for the communications we need to perform.
One important thing I’ve learned over 40+ years: if you don’t use it regularly, don’t count on it in an emergency. That’s true of antennas and other equipment as well as supplies, skills, procedures, etc. Not only do we need to plan in advance, but we also need to practice regularly.
Desired Characteristics for Emergency Antennas
Obviously this will depend to a large extent on the nature of the emergency and the required response. But there are some common features that should at least be considered in your planning, even if it turns out that they don’t apply in your specific situation.
- Effective. It does the job you need it to do. Generally this means it operates on the required bands with a radiation pattern suitable (both vertical and horizontal) to work the stations you need to. (This also should include susceptibility to picking up local noise.)
- Efficient. When operating from emergency generators or batteries, being able to make contacts using lower power allows you to stay on the air longer.
- Simple. When you have to set up an antenna in the dark, in bad weather, in an unfamiliar location, you want it as simple as possible (while still working adequately, of course). And you might have to give the antenna to someone else to set up. If the antenna is broken, that should be easy to see (and, hopefully easy to fix).
- Portable. Emergencies don’t always happen in convenient locations, or our stations may be damaged and we have to operate from elsewhere. I have a whole section on Portable Antennas.
- Adaptable. Emergencies are unpredictable. I might find that my ham antennas need to be used by another group on 4.5 MHz. Or I may have to set up the antenna in different conditions than I am used to. In fact, adaptability is an important factor for people as well as for antennas.
- Expendable. If I set up an antenna at an emergency site and turn the station over to another set of operators, I can’t expect to take the antenna with me when I leave. Your antenna might be needed by another team at a different site, or you may have to evacuate your site in a hurry due to approaching fire or a lava flow. It shouldn’t be a financial hardship on you if you don’t get your antenna back afterwards. (Marking each antenna with your name, callsign, and phone number may increase the chance of it being returned later.) And, as a group, it may be better to have a large number of inexpensive but adequate homemade antennas than a few expensive commercial ones.
Antennas to Survive an Emergency
Even for government agencies with plenty of money, this isn’t always as easy as it might seem, because emergencies can take many forms. We have a lot of engineering data to consult about wind loading and allowable bending stress on aluminum and steel, that allow us to design antennas to survive up to a particular wind speed for a hurricane. (Don’t forget to make sure the tower guy anchors will hold in wet ground.) But if the building floods, or collapses in an earthquake, that may not keep us on the air. And as we see storm intensities increase over the years, there is always the question of just how high of a wind speed (or earthquake intensity) we should design for.
For those of us with a finite budget, often a better approach is to install antennas that will survive if the building does. For example, a wire loop around the outside edge of a roof (especially on the inside of the trim boards), is likely to survive unless the roof is blown off or the building collapses. The same may be true of some wire antennas on the roof, or elevated only slightly above it, or antennas installed in an attic. Here in Oregon we often nail strips of zinc along the peak of our roofs to try to reduce the growth of moss (it doesn’t work that well), and those could be arranged as a dipole, doublet, or end-fed antenna (although the losses in the underlying roof material must be considered) These may not be the primary station antenna in normal times, but can serve as an emergency backup if needed.
Antennas to put up in an emergency.
In most cases, emergency communications are most important for the recovery phase of an emergency, rather than during a hurricane or earthquake. Having a temporary or portable antenna available (along with supports as needed) makes it easier to get back on the air even if the regular station antennas are down or the station has to be moved to another location.
It is worthwhile planning where you will store such a portable antenna. Obviously, if it is stored inside a building that collapses, it may not be easily available. Wooden buildings are less likely to totally collapse, but may shift in an earthquake and jam doors closed. In a storeroom where the door opens inwards, falling shelves or boxes may block the door from opening. Outside doors that open outwards can be blocked by drifted snow or volcanic ash that needs to be moved out of the way.
While you are at it, plan for the necessary supports as well. Plan in advance where you can lash a support to a fence post or other support that isn’t dependent on a building.
In some cases we still may be caught without a suitable antenna, and have to improvise one with materials we can find. 75 ohm television cable can be pressed into service in place of 50 ohm coax, or various types of speaker cable, power cord, or twisted pair can be used instead. CAT-5 computer network cables can be stripped down: a single twisted pair serves as a 100 ohm feedline, while the remaining wires can be configured as an antenna. (Consider a 200 ohm loop antenna with a 1/4 or 3/4 wavelength feedline.) The same materials can be used for the antenna elements, along with fence wire (even barbed wire), or welding wire. (Steel has higher losses than copper or aluminum, but it may be the best you can find.) A request to a maintenance department or utility repair crew might provide what you need (even if it was intended for a different use), along with a spool of rope or twine to install it. Especially for multi-band operation, an antenna tuner at the station will simplify the task.
VHF/UHF antennas can be built using stiff copper wire, tin cans soldered together, wire coat hangers, aluminum kitchen foil, or strips of metal flashing.
Possible supports include whatever remains standing of buildings or trees, flagpoles, ladders, irrigation pipes, pieces of fence rail, or handles for brooms, mops, or paint rollers.