HF Radio: Cross-Country Communication Without Infrastructure

How HF Radio Works

VHF/UHF signals — the frequencies your handheld radio uses — travel in essentially straight lines. They hit hills, buildings, and the curvature of the earth. Without a repeater to relay them, the practical range is 2-20 miles.

HF signals (roughly 3-30 MHz) behave differently. At the right frequencies, they travel upward, strike the ionosphere — the electrically charged layer of atmosphere at 30-250 miles altitude — and refract back to earth at distances hundreds to thousands of miles from the transmitter. The signal skips. Multiple skips can carry a signal around the world.

This is not cutting-edge technology. It's been understood since the early 20th century. It works because of basic physics — charged particles in the ionosphere bend radio waves. No satellites, no towers, no internet required.

The challenge is that the ionosphere changes. Solar activity, time of day, season, and sunspot cycle all affect which frequencies propagate where and how far. Learning to read propagation conditions is a core HF operating skill.

Band Selection

You don't get to choose one frequency and call it done. Different HF bands work at different times of day and for different distances. For emergency preparedness, the three most important bands are:

40 meters (7.0-7.300 MHz) — The Primary Emergency Band

The workhorse. During daylight, 40m covers regional distances (100-800 miles). As the sun sets and the D-layer fades, range extends dramatically. Evening 40m regularly produces contacts 1,000-3,000 miles out. After midnight, skip distances can reach across the continent.

The primary emergency voice frequency for the Americas is 7.230 MHz (ARRL band plan). General class operators have phone privileges from 7.175-7.300 MHz. For digital modes (Winlink, JS8Call), the primary 40m frequencies are around 7.078-7.080 MHz.

If you have one antenna and one emergency band, make it 40 meters.

80 meters (3.5-4.000 MHz) — Regional Night Band

80m is a regional band, excellent within 500-1,000 miles at night. State and regional emergency nets often run on 80m. During the day, range shortens to 100-300 miles as the D-layer absorbs the signal. Phone privileges for General class start at 3.800 MHz.

A state emergency coordination net running on 3.885 MHz at 8:00 PM can be heard clearly across an entire state. 80m is where you'd monitor for regional emergency nets.

20 meters (14.000-14.350 MHz) — Daytime International Band

20m propagation peaks during daylight hours, reflecting off the F-layer for distances of 1,500-8,000 miles. Less reliable than 40m for domestic emergency use, but 20m is how you reach stations in Europe, South America, or the Pacific if needed. International emergency calling frequency is 14.300 MHz.

Propagation by Time of Day

Understanding when to transmit is as important as what frequency to use.

| Time | 160m | 80m | 40m | 20m | Notes | |---|---|---|---|---|---| | Sunrise | Fair | Fair | Short skip | Building | D-layer forming | | Morning | Poor | Short skip | 300-600 mi | Good (1,500+ mi) | D-layer absorbs lower bands | | Noon | Poor | Poor | 500-800 mi | Excellent | Full D-layer absorption | | Afternoon | Poor | Poor | 500-800 mi | Good | D-layer still active | | Sunset | Building | Building | 1,000+ mi | Fading | D-layer fading | | Evening | Good | 500-1,000 mi | 1,000-3,000 mi | Poor-fair | Best 40m window | | Midnight | Excellent | 500-1,500 mi | 2,000-3,500 mi | Poor | Maximum skip distances | | Pre-dawn | Excellent | Good | 1,500-3,000 mi | Fair | Still extended skip |

For coast-to-coast contact within the continental US: 40m, 6-11 PM local time. For regional contact (same state or adjacent states): 80m, after dark. For contact with stations outside North America: 20m, midday.

Operating Procedures

HF has established conventions that make emergency communication more efficient. Knowing them matters — a crowded 40m band during a regional emergency has dozens of operators competing for airtime, and operators who don't know procedure create chaos.

Before transmitting:

• Listen first. Listen for several minutes. Determine if the frequency is in use.
• "QRL?" (Is this frequency in use?) is the standard check before transmitting.
• On busy bands, identify a clear frequency or monitor established nets.

Making contact (calling CQ): "CQ CQ CQ, this is Whiskey One Alpha Bravo, calling CQ and standing by."

Wait 10-15 seconds. If no response, repeat. After 3-4 attempts on the same frequency with no answer, try a different frequency.

Emergency calls: "MAYDAY MAYDAY MAYDAY — [call sign] — [position] — [nature of emergency] — [assistance needed] — [over]"

The MAYDAY call supersedes all other traffic. Any station hearing a MAYDAY is obligated to respond or stand by for emergency traffic.

Net operation: Most emergency traffic moves through organized nets — scheduled operations with a Net Control Station (NCS) managing traffic. The NCS identifies who wants to check in, takes each station in turn, and prioritizes emergency traffic. Follow the NCS's direction. Check in with your call sign when the NCS asks for check-ins. Don't transmit unless the NCS recognizes you.

Antenna Fundamentals

A wire dipole is the simplest HF antenna and works well for emergency communication. No tuner, no special equipment — cut the wire to length, hang it, connect to the radio.

40-meter dipole dimensions:

• Total length: approximately 66 feet (33 feet per leg)
• More precisely: 468 / frequency in MHz = total length in feet
• For 7.200 MHz center frequency: 468 / 7.2 = 65 feet total, 32.5 feet per leg

Installation: Support the center with a mast, tree, or other structure. Run each leg out horizontally (or as close to horizontal as terrain allows) toward separate support points. The center connection (feedpoint) connects to coaxial cable (RG-8X or RG-58 for runs under 100 feet) running to the radio.

The dipole can also be installed inverted-V (center high, legs dropping at 45 degrees to ground anchors) when two far-apart supports aren't available. Performance drops slightly compared to horizontal, but it's a workable emergency installation.

Antenna height: Any height works. Higher is better for long distances; lower favors more regional distances. For emergency use, get the antenna up as high as convenient and don't overthink it.

End-fed half-wave (EFHW): A popular alternative to the center-fed dipole. One end connects to the radio via a matching transformer; the other end anchors anywhere. Easier to deploy in the field since you need only one high support point. Commercial EFHW antennas for 40m run $80-150. DIY versions use commercially available matching units ($20-40) plus wire.

Power

HF transceivers run on 12-16V DC. A quality switching power supply (25-30 amp capacity for 100W operation) costs $80-150 for home use. The Powerwerx SS-30DV and similar supplies are reliable and appropriately sized.

For emergency operation without grid power, a 100Ah lithium iron phosphate (LiFePO4) battery provides approximately:

• 1-1.5 hours at 100W transmit
• 3-4 hours at 25-50W transmit (usually sufficient for regional emergency contacts)
• 8-12 hours monitoring/receive only

Pair battery operation with a solar charging system for extended emergency use. A 100W solar panel in reasonable sunlight can maintain battery state during receive-heavy monitoring operations.

Power reduction: 100W is the standard output. 25-50W often makes contacts just as well in good propagation conditions. Running at lower power extends battery life and reduces RF exposure. If you're getting reliable contacts at 50W, no need to run 100W.

Digital Modes

Voice isn't the only option. Several digital modes allow text-based HF communication, and some work at signal levels too weak for voice copy.

Winlink: Email over radio. Winlink gateways receive your transmission and forward emails to any address. No internet required on your end — you're using radio to reach the Winlink network, which bridges to the internet. For an emergency operator isolated from internet, Winlink allows email communication with anyone worldwide. See the Winlink article for details.

JS8Call: Digital messaging mode based on FT8. Allows text messages between stations, stores-and-forward messaging, and relay. Works at very low signal levels. Less structured than Winlink — more like a radio-based SMS system.

FT8/WSPR: Propagation modes, not communication modes. Useful for determining if propagation exists to a region before committing to a voice or Winlink contact.

When HF Communication Is Critical

You need HF when:

• The emergency affects your entire region and local repeaters are down or congested
• You need to contact family members in another state
• You need information from outside the affected area (news, status updates, coordination with distant resources)
• Local emergency networks are overwhelmed

A 2019 analysis of communication capabilities during Hurricane Michael found that amateur HF operators maintained communication with national coordination networks for 96 hours after all commercial infrastructure failed in the affected area. They were using gear equivalent to what's described in this article — HF transceivers, wire antennas, and battery power.

This is not a theoretical capability. It works, it's proven, and the equipment is accessible.

The investment — a General license, an HF transceiver, and a wire antenna — creates a communication option that is independent of every infrastructure system that fails in a major emergency.