Communications

Radio is both how you reach the rest of your unit and how the enemy finds you, and modern electronic warfare has sharpened both edges. The threat is concrete: Russia's Murmansk-BN can blanket high-frequency radio out to about 300 kilometers and listen across the shortwave bands much farther,³ and in April 2024 NATO and Ukraine stood up a dedicated Electronic Warfare Coalition, now thirteen nations, to keep pace.⁴ Learning how radio works is the first step to using it without being located.

Frequency and Wavelength

A radio wave is a repeating ripple, and its wavelength is the distance from one crest to the next, while its frequency is how many of those cycles pass each second, counted in hertz.¹ A thousand hertz make a kilohertz, a million make a megahertz, and a billion make a gigahertz.

Wavelength and frequency are two sides of one coin: as one rises, the other falls. The shortcut is the number 300 — divide it by the frequency in megahertz to get the wavelength in meters, or divide it by the wavelength to get the frequency. So 144 MHz works out to about two meters, which is why amateurs call it the two-meter band.¹

The Decibel System

Radio math runs on decibels because the power levels involved span an enormous range, and a decibel states a ratio between two of them on a logarithmic scale.² When the reference is one milliwatt the unit becomes the dBm, an absolute measure of power, and the anchor to memorize is that one watt equals 30 dBm. Two rules cover most of the mental math: doubling the power adds 3 dB, and multiplying it by ten adds 10 dB.²

Frequency Bands

Sources

1. RF Theory Read-Ahead: Fundamentals (Light Fighter Library) — wavelength and frequency, the “divide 300” shortcut, the frequency bands, and the antenna-size trade-off.
2. Electronic Warfare Fundamentals, Vol. I: Radio Fundamentals (Light Fighter Library) — decibels and dBm, and the 3 dB (double) / 10 dB (ten-times) rules.
3. Army Recognition — Russia's Murmansk-BN jams HF/shortwave out to about 300 km and reconnoiters much farther.
4. Kyiv Independent — NATO and Ukraine launched the Electronic Warfare Coalition in April 2024; it now has thirteen signatories.

A radio signal almost never travels in a clean straight line from one antenna to the other. It bends, bounces, scatters, and fades on the way, and knowing how it does that is what lets you place an antenna, pick a frequency, and judge whether a link will hold.¹

Propagation Effects

Five things happen to a signal in transit. It attenuates, losing strength with distance in a predictable way. It reflects, bouncing off metal, water, and the ground at equal angles. It refracts, bending as it crosses between air layers of different density. It diffracts, curling around the edge of a hill or building, which is how a VHF signal sometimes reaches past high ground. And it is absorbed, its energy turning to heat as it passes through walls, foliage, or heavy rain.¹

Often a signal does several of these at once and arrives by more than one path. The copies reach the antenna at slightly different times and phases, and they either reinforce or cancel each other, which is why moving a few feet in a built-up area can turn a dead channel into a clear one.¹

Path Loss Calculations

Path loss is just attenuation put to numbers. In open free space a signal loses 6 dB every time the distance doubles, or 20 dB every time it grows tenfold. Add buildings, trees, and terrain, and the loss roughly doubles — to about 12 dB per doubling and 40 dB per tenfold step.¹

Weather Effects

Weather reshapes propagation, sometimes in your favor. A temperature inversion can form a duct that carries VHF and UHF signals far past their normal line-of-sight range.² Higher up the spectrum the weather works against you: humidity raises absorption at microwave frequencies, rain attenuates hard above 10 GHz, and fog, which barely touches radio below 30 GHz, will still degrade an optical link.^{1, 2}

Sources

1. TC 9-64: Wave Propagation, Transmission Lines, and Antennas (Light Fighter Library) — reflection, refraction, diffraction, absorption, multipath, and free-space / path-loss behavior.
2. The VHF/UHF Primer: An Introduction to Propagation (Light Fighter Library) — tropospheric ducting and bending, and how weather extends or limits VHF/UHF range.

Forty-eight to four hundred kilometers up, the sun strips electrons from the thin air and turns a band of the atmosphere into a mirror for radio. That mirror — the ionosphere — bends HF signals back to Earth, which is how a shortwave radio reaches across a continent with no satellite and no repeater.¹ The catch is that the sun makes the mirror, so it shifts with the hour, the season, and the eleven-year solar cycle.^{1, 3}

Ionospheric Layers

The ionosphere is not one mirror but four stacked layers — D, E, F1, and F2, lowest to highest — and each one treats radio differently. Their heights and strength rise and fall with the time of day, the season, and how active the sun is.¹

MUF and LUF

At any moment the ionosphere returns only a band of frequencies. Above the Maximum Usable Frequency (MUF) a signal punches through the layer and escapes to space; below the Lowest Usable Frequency (LUF) it is absorbed before it can bounce. You work in the window between them, and that window slides all day.¹

By day the D layer absorbs the low end and drives the LUF up; at night the D layer vanishes and the low bands open. The MUF usually peaks in the afternoon, when sunlight has the F layer most strongly ionized.¹

Take-Off Angles and Distance

How far a hop reaches depends on the angle at which the signal leaves your antenna. A low angle skims into the ionosphere and comes down far away; a high angle comes down close; and a near-vertical shot rains the signal straight back down over everything around you, with no dead zone in between.¹

Sources

1. High Frequency Radio Theory, Class 1 (Light Fighter Library) — ionospheric layers, MUF and LUF, skip distance and take-off angle.
2. HF Class 4: NVIS and Antenna Types (Light Fighter Library) — near-vertical incidence skywave: take-off angle, 2–10 MHz with the day/night split, and the low horizontal antenna.
3. NOAA Space Weather Prediction Center — Solar Cycle 25 peaked around 2024; solar flares and geomagnetic storms (e.g. May 2024) black out HF and lift aurora to low latitudes.

An antenna is the part of the radio that actually touches the air, turning your transmitter's electricity into a wave and catching the wave on the way back.¹ Which antenna you hang decides your range, the shape of your coverage, and — in a world full of direction-finders — how much of your signal leaks toward the wrong people. It is also the one piece you can build from a length of wire when you have nothing else.^{1, 2}

Antenna Length Calculations

An antenna works best when its length matches the wave it is meant to carry, and the half-wave dipole is the yardstick everything else is measured against.¹ The length in feet is simply 468 divided by the frequency in megahertz for a half-wave, or 234 divided by it for the quarter-wave vertical that fakes the missing half against a ground plane.²

Antenna Types

The half-wave dipole is two quarter-wave legs fed in the middle. It adds a modest 2.15 dBi of gain and radiates in a figure-eight broadside to the wire, and it is about the simplest useful antenna there is.¹

A quarter-wave vertical stands one leg straight up and uses a ground plane — radials, a vehicle body, or the earth itself — as the other half. It throws an even circle around you at a low angle, which is what you want for reaching far.¹

A long wire runs several wavelengths and concentrates its gain along the direction it points, but it needs a termination resistor to behave and the room to stretch out, so it suits a fixed site.¹

Gain and Beamwidth

Gain is not free power; it is focus — how tightly an antenna concentrates its energy in one direction against a reference.¹ Measured against an ideal point source it is written in dBi; measured against a dipole it is dBd, and you add 2.15 to turn dBd into dBi.¹

Beamwidth is the width of that focused lobe, measured between the half-power points; a narrow beam means high gain and a pointed pattern, where a Yagi might run 30 to 60 degrees while an omnidirectional antenna covers the full circle.¹ That focus has a second value on a contested net: a directional antenna pours your signal toward the station you want and starves a direction-finder sitting off to the side, so the right antenna is also a quieter one.³

Sources

1. MCRP 8-10B.11 Antenna Handbook (Light Fighter Library) — antenna types (dipole, vertical, inverted-vee, long wire), gain and directivity, beamwidth, and take-off angle.
2. HF Antenna Cookbook (Light Fighter Library) — the 468 / 234-over-frequency length formulas and field-expedient wire dipoles.
3. LPI/LPD secure communications (arXiv, 2024) — a directional antenna's energy concentrates in the main beam, so off-axis it is far harder to intercept or direction-find.

A link budget is the radio version of a fuel calculation: you add up every gain and subtract every loss between your transmitter and the far receiver, and if more signal arrives than the receiver needs to hear, the link works.¹ Running it beforehand tells you whether you need more antenna, more power, or a relay — before you find out the hard way.

EIRP Calculation

Start at your own antenna. Effective isotropic radiated power (EIRP) is how much signal actually leaves it toward the target: take the transmitter's output, subtract whatever the feedline eats, and add the antenna's gain.¹

EIRP = Transmitter Power + Antenna Gain - Feedline Loss

Example: A 5-watt transmitter (37 dBm) connected through 2 dB of cable loss to a 6 dBi antenna produces 37 + 6 - 2 = 41 dBm EIRP, equivalent to 12.6 watts radiated toward the target.

Receiver Sensitivity

At the far end, the receiver can only hear down to a floor called its sensitivity — the weakest signal it can still turn into usable output, written as a deeply negative dBm, where more negative means a better ear.¹ A good amateur HF receiver hears down around -130 to -140 dBm; a commercial VHF/UHF set, -115 to -125.

Link Margin

Link margin is the cushion: how far the signal that arrives sits above that sensitivity floor. A positive margin means the link should hold; a negative one means it fails outright. In the real world you want 10 to 20 dB of margin in hand, because fading, interference, and weather will spend it.¹

Sources

1. Electronic Warfare Fundamentals, Vol. I: Radio Fundamentals (Light Fighter Library) — effective radiated power, receiver sensitivity (minimum discernible signal), path loss, and link margin.
2. VOACAP Online User's Manual & Cloud RF field guides (Light Fighter Library) — the propagation tools that compute a link budget: VOACAP for HF ionospheric paths, Cloud RF for line-of-sight terrain.

DMR — Digital Mobile Radio — is an open digital voice standard, and on the same channel an analog radio would use for one conversation it carries two, with cleaner audio and the option to encrypt.¹ The gains come with a digital catch: DMR holds full quality right to the edge of range and then drops out all at once, where analog would simply get noisy.

DMR Technology

DMR splits one 12.5 kHz channel into two time slots, chopping each transmission into 30-millisecond packets that interleave, so two separate conversations can share the frequency at once.^{1, 2}

Three settings steer a DMR call. The color code is the digital version of an analog tone — both radios must match it to work through the same repeater. The time slot picks which of the two channels you transmit on. And the talkgroup is the address: everyone listening to that group number, on that slot, hears you, and no one else does.²

All of it — frequencies, color codes, slots, talkgroups, and contacts — lives in a codeplug, the configuration file you load onto the radio before it will do anything.²

Advantages Over Analog

• Better voice quality through digital error correction
• Enhanced coverage and signal reliability in marginal conditions
• Two simultaneous conversations per frequency (TDMA)
• Extended battery life from efficient duty cycle (transmitting only 50% of time)
• Built-in encryption options from basic to AES-256
• Data capabilities including text messaging and GPS tracking
• Interoperability between manufacturers using open standard

Networked DMR

Most amateur DMR does not stay local. A hotspot — a box the size of a deck of cards — links your radio to a worldwide network like Brandmeister over the internet, so a low-power handheld can reach a talkgroup on another continent.² That reach has a cost you have to weigh: your traffic leaves the air and crosses the internet to a server that routes and logs it, so networked DMR is global and convenient, but it is neither local nor private.²

DMR Encryption

DMR can encrypt its voice and data, and AES-256 is the standard for anything that matters — the 256-bit Advanced Encryption Standard, secure against any known attack when the keys are managed well. The two older options are weaker, and worth knowing mainly so you avoid them: Basic Privacy is a scramble a determined listener breaks quickly, and Enhanced Privacy is a 40-bit proprietary cipher in between.¹

What you may legally encrypt depends on the band, not the radio. On licensed business and commercial channels — FCC Part 90 — AES-256 is permitted and routine, and a Part 90 license gives you your own slice of spectrum to run it on. On the amateur bands it is flatly prohibited, because FCC §97.113 bars obscuring a message's meaning. The rule of thumb: encrypt on your commercial frequencies, and keep the ham bands in the clear.³

Sources

1. DMR Programming Workshop (Rocky Mountain Ham Radio) (Light Fighter Library) — DMR overview, two-slot TDMA, the analog-vs-digital trade, and the privacy / encryption modes.
2. EvoHam, “What Is DMR in Ham Radio” — color codes, time slots, talkgroups, codeplugs, and hotspot / Brandmeister networking over the internet.
3. FCC Part 90 vs Part 97 on encryption — AES-256 is legal and standard on licensed commercial (Part 90) channels, and prohibited on the amateur bands under FCC §97.113.

VHF and UHF are the everyday workhorses of tactical radio — short to medium range, sensible antenna sizes, and gear that runs from a twenty-dollar handheld to a military manpack.¹ They are also the most crowded and most contested bands, the ones an enemy jams and direction-finds first, so how you run them matters as much as the radio you run.

Common Frequency Allocations

In the United States several VHF and UHF services let you transmit with no license or a simple one, each with its own slice of band and its own power ceiling.³

MURS Channels

MURS — the Multi-Use Radio Service — gives you five license-free VHF channels at up to two watts. Its lower frequencies push through foliage and walls a little better than the UHF services, and it stays less crowded than FRS or GMRS in most places.³

Range Expectations

On VHF and UHF the signal travels in nearly straight lines to a horizon set by how high the antenna sits, so range depends far more on terrain and antenna height than on transmitter power.¹ Handheld to handheld on flat ground runs one to five miles; handheld to an elevated base, five to twenty; two elevated bases, twenty to fifty or more. A city cuts all of those down hard.

The numbers explain why operators chase height, not watts. Going from 5 to 50 watts is a tenfold jump in power, but it buys only about 10 dB — in real terrain that barely doubles your range, nowhere near tenfold. Lifting the antenna from six feet to thirty often beats it, because it pushes your radio horizon farther out.¹ Spend your effort on antenna position before power.

Sources

1. The VHF/UHF Primer: An Introduction to Propagation (Light Fighter Library) — line-of-sight propagation, the radio horizon set by antenna height, realistic range, and urban-vs-foliage behavior.
2. SINCGARS Familiarization (AN/PRC-119) (Light Fighter Library) — frequency-hopping and anti-jam (ECCM) operation on tactical VHF.
3. FCC Personal Radio Services — the FRS, GMRS, MURS, and CB bands, power limits, and licensing.

High-frequency radio is having a comeback, and electronic warfare is the reason. When satellites are jammed and cell networks are gone, a 3-to-30 MHz signal bouncing off the ionosphere still crosses a continent with no infrastructure in between, and it is hard to jam because its frequencies have to be re-tuned to the shifting ionosphere constantly anyway.³ For a team that needs to talk when everything else is down, nothing else matches it.¹

Ground Wave and Sky Wave

HF reaches in two ways. The ground wave hugs the surface and follows the curve of the earth for the first tens of miles, which is good for short local links. The sky wave climbs to the ionosphere and refracts back down, and that is what carries HF from regional range to the far side of the world.²

The Xiegu G90

You do not need a manpack to get on HF. The Xiegu G90 is a two-pound, twenty-watt transceiver that receives from 0.5 to 30 MHz, transmits on the amateur bands in voice and digital modes, and carries its own antenna tuner — a deployable HF station for a few hundred dollars.⁴

Band Selection

Which HF band works depends on the time of day, the season, and the state of the sun. The low bands, 3 to 7 MHz, carry long distances at night and serve NVIS by day; the high bands, 14 to 28 MHz, open for worldwide work in daylight but go quiet at night, and the very highest only come alive when the sun is active.¹

Automatic Link Establishment

Picking the right HF frequency by hand takes practice and a feel for the ionosphere. Automatic link establishment, or ALE, does it for you: the radio quietly sounds a list of channels, measures which ones are reaching the station you want, and sets up the call on the best one — in under a second on modern gear, with no knowledge of the ionosphere on your part.^{2, 3} It is what has turned HF from a specialist's art back into something anyone on a team can use.

Sources

1. High Frequency Radio Theory, Class 1 (Light Fighter Library) — HF capability, ground wave vs sky wave, and band selection by time of day and solar conditions.
2. FM 6-02.74: Multi-Service TTP for HF-ALE Radios (Light Fighter Library) — automatic link establishment at the operator level: sounding, link-quality measurement, and best-channel selection.
3. Shephard Media, “The HF Renaissance” — HF's revival as a jam-resistant, infrastructure-free alternative to vulnerable SATCOM, and sub-second ALE.
4. EmComm Tools: Xiegu G90 Field Manual (Light Fighter Library) — the G90's coverage, power, modes, weight, and built-in antenna tuner.

JS8Call lets you pass a text message over HF when the band is too weak to even hear a voice. Built on the FT8 weak-signal engine, it digs a readable message out of the noise at -24 dB signal-to-noise, where single-sideband voice needs about +10 dB — a 34-decibel gap, or roughly a thousand times less power for the same reach.¹ That makes it the off-grid messaging mode of choice: keyboard-to-keyboard chat, store-and-forward, and automatic relay across a net of stations, all on a few watts and a wire antenna.²

Key Features

• Weak signal performance: reliable at -24 dB SNR
• Store-and-forward messaging between stations
• Automatic message relay through network of stations
• Keyboard-to-keyboard QSO capability unlike FT8
• Heartbeat feature announces station presence
• Multiple speed modes: Slow, Normal, Fast, Turbo
• Integration with radio CAT control for automatic operation

Speed Modes

Operating Procedures

1. Ensure computer clock is synchronized within 2 seconds (JS8 displays UTC, not local time)
2. Launch JS8Call and verify connection to radio
3. Select appropriate frequency (40m: 7.078 MHz, 20m: 14.078 MHz are common)
4. Configure digital settings and audio levels per radio specifications
5. Set power output appropriately - 5 watts is often sufficient
6. Position on quiet spot in waterfall between 1000-1800 Hz (1500 Hz recommended)
7. For G90: Long press TUNE button to enable automatic antenna tuner
8. Monitor waterfall for activity before transmitting

Requesting SNR Report

Signal-to-noise ratio reports establish link quality. An SNR of 0 dB or better indicates voice (SSB) or faster JS8 modes are likely possible. Negative values down to -24 dB can still support normal JS8 messaging.

1. Verify your waterfall offset is clear of other activity
2. Right-click on target callsign or group in the callsign window
3. Select Directed to [callsign] followed by SNR? command
4. Wait for response - may take several transmission cycles
5. If no response in Normal mode, try Slow mode for better sensitivity
6. If still no response, send heartbeat (HB button) to announce presence

Sending Messages

1. Verify waterfall offset is clear
2. Right-click target callsign in callsign window
3. Select Directed to [callsign] then MSG [MESSAGE] - store in inbox
4. Replace [MESSAGE] with your actual message text
5. Press ENTER or Send button to transmit

Fast Data: VARA and the Open-Source Modems

JS8 is built for tiny messages in terrible conditions; when the band is decent and you need to move a file, a form, or an email, you switch to a fast data modem. VARA, a proprietary modem by EA5HVK, is the de-facto standard behind Winlink radio email — its free version crawls near 180 bits per second, while the paid license, about seventy dollars, opens it up to roughly 8,500.³ The open-source answers are FreeDATA, which moves files and messages over the Codec2 HF modems, plus the older ARDOP and the VARA-inspired Mercury — free, cross-platform, and tied to no vendor.⁴

Encrypted HF

None of these modems encrypts anything on its own — they are pipes, and VARA's built-in AES option is licensed for non-amateur use only.³ Real privacy on HF comes from what you run through the pipe: the Reticulum network stack encrypts every packet end-to-end by default, and projects like ReticulumHF carry it over the air using FreeDV data modes, giving you genuinely private HF links.^{5, 6}

One rule governs all of it in the United States: FCC §97.113 forbids encryption on the amateur bands, so encrypted HF is for grid-down operation, licensed government and MARS use, or non-amateur services — built and ready, not for everyday ham traffic.⁷

Sources

1. JS8Call — the mode and its software: FT8-derived weak-signal messaging, the Slow/Normal/Fast/Turbo speed modes and sensitivities, the 7.078 / 14.078 MHz calling frequencies, the 2-second UTC time-sync requirement, and heartbeat and relay.
2. OH8STN, Off-Grid Ham Radio & AmRRON — JS8Call as an off-grid, low-power emergency-communications messaging tool, and its open, unencrypted nature.
3. VARA HF (EA5HVK) — the proprietary fast HF data modem behind Winlink; free ~180 bps versus paid ~8,500 bps, with an AES option licensed for non-amateur use only.
4. FreeDATA (DJ2LS) — open-source, cross-platform file and message transfer over the Codec2 HF modems; the open alternative to VARA.
5. Reticulum Network Stack — a cryptographic networking stack that encrypts every packet end-to-end by default, over LoRa, packet radio, Wi-Fi, and HF.
6. ReticulumHF — encrypted communication over HF radio, running the Reticulum stack over FreeDV data modes.
7. FCC 47 CFR §97.113 — messages encoded to obscure their meaning (encryption) are prohibited on the US amateur bands.

A communications plan with only one way to talk is not a plan, because the one thing you can count on is that your best method will fail at the worst time. PACE answers that by lining up four ways to reach each other — Primary, Alternate, Contingency, and Emergency — and a rule for falling back through them: when the primary dies, you move to the next that still works, without a discussion.¹

PACE Framework

The four tiers are ranked by capability, not preference: the higher the tier the more it can do, and the lower the tier the more certain it is to work at all.¹

Example PACE Plan

A good plan makes each tier fail differently, so a single problem — one jammed band, one dead repeater — cannot take two tiers down at once.¹

PACE Principles

• Each tier should use different technology or path to avoid common failure modes
• All participants must know and have tested each tier
• Transition triggers should be explicit (time, event, or command)
• Lower tiers may have reduced capability but must work reliably
• Exercise all tiers regularly to maintain proficiency

Signal Operating Instructions

A PACE plan only helps if everyone carries the same one, so it is written down and handed out before the operation as Signal Operating Instructions, the SOI. The SOI sets the callsigns, the frequencies for each tier, the authentication and brevity codes, the check-in schedule, and the triggers for switching tiers.² Every operator carries the current copy and knows what is in it.

• Callsign roster for all elements
• PACE frequencies and channels for each tier
• Authentication tables or procedures
• Brevity codes and prowords
• Check-in schedule (times, formats, responses)
• Transition triggers and procedures
• Emergency distress procedures
• Encryption keys or key changeover schedule

Sources

1. RTO Basics Course: Radio Theory and PACE Planning (Light Fighter Library) — PACE as a resilient-communications framework, the four tiers ranked by capability, and the fall-back discipline.
2. Operationalize Communications: PACE Planning Brief (Light Fighter Library) — building a PACE plan into Signal Operating Instructions with callsigns, frequencies, authentication, and transition triggers.

Every time you key the microphone, you broadcast your position to anyone listening with the right gear. On a quiet net that is an abstract risk; on a modern front it is a lethal one, because direction-finding is now the front half of a kill chain — locate the emitter, then drop artillery or an FPV drone on it, often within minutes.³ The whole craft of field radio comes down to talking without being found.

DF Techniques

A direction-finder fixes you in one of a few ways. Time difference of arrival compares the instant your signal reaches several receivers; with their positions known and their clocks synchronized to the microsecond, the differences solve for your location.¹

Frequency difference of arrival works from motion instead: a moving receiver on an aircraft or satellite reads the Doppler shift in your signal and turns it into a direction.¹

Closer in, the classic Watson-Watt method compares signal strength across crossed antenna loops to read a bearing in real time on simple hardware, while correlative interferometry compares the phase across an array of antennas for a sharper fix — the method inside most modern tactical DF sets.¹

Protective Measures

You cannot beat a direction-finder, only deny it a clean shot, and every measure below does that by shrinking the signal it has to work with.²

• Minimize transmission time - shorter is harder to locate
• Reduce power to minimum necessary for communications
• Use directional antennas pointed away from threat areas
• Vary transmission locations when possible
• Use terrain masking between you and known DF sites
• Consider receive-only operation when inside threat WEZ
• Digital modes with short burst transmissions reduce exposure

Geolocation Accuracy

How precisely they pin you depends on the technique and the geometry. One bearing from one site gives a direction but no range; two or more bearings cross into an error ellipse; and a good time-difference fix with several synchronized receivers can put you inside a hundred meters — close enough to shoot.¹

Sources

1. Electronic Warfare Fundamentals & Direction Finding (Light Fighter Library) — the DF techniques (time- and frequency-difference of arrival, Watson-Watt, correlative interferometry) and geolocation accuracy by geometry.
2. Signature Management (EPEMCON) SOP (Light Fighter Library) — emission control: minimizing transmission time, power, and pattern to deny a direction-finder a fix.
3. CEPA, “Adaptation Under Fire” — direction-finding and jammer-locators feeding artillery and drone strikes, and the move to frequency-hopping radios.

These are the numbers you reach for in the field without a calculator — antenna lengths, skip distances, and band edges — laid out to read off a phone screen or a laminated card.¹

Antenna Length Formulas

These formulas size an HF antenna, with the standard 0.95 velocity correction folded in across the 3-to-50 MHz range, and the same numbers give the height to hang a wire antenna for NVIS.²

Common HF Antenna Lengths

Take-Off Angle vs Distance (F2 Layer)

The angle at which your signal enters the ionosphere determines skip distance. Lower angles produce longer range. These distances assume F2 layer propagation which is the primary layer for HF communications.

HF Antenna Types Comparison

Inverted V Apex Angles

When constructing an Inverted V antenna, the apex angle affects performance. Steeper angles (closer to 90°) provide more omnidirectional coverage while flatter angles increase gain in the broadside direction.

Frequency Band Reference

Ionospheric Layers

The ionosphere consists of distinct layers that affect HF propagation differently. During daylight, all layers are present. At night, the D layer disappears and F1/F2 combine, generally improving long-distance propagation.

Sources

1. HF Quick Reference Guide (Light Fighter Library) — the field reference tables: antenna lengths, take-off angle versus skip distance, the frequency-band chart, and the ionospheric layers.
2. MCRP 8-10B.11 Antenna Handbook & HF Antenna Cookbook (Light Fighter Library) — the 468 / 234-over-frequency antenna-length formulas and the inverted-V apex angles.