Royal Army College

Lesson Overview

Lesson 02 built the plan: the comms estimate and the PACE plan name who must talk to whom, by what means, and what the fallback is when the first means fails. This lesson gives you the physical understanding that makes those choices sound and lets you put a link right when it goes quiet. A signals NCO who knows only how to switch a radio on can call a check and hope. One who understands how a signal actually travels, why it stops, and what really extends it can look at a map and a hill and say, before anyone moves, where a link will hold and where it will break, and can fix a dead net by changing one thing on purpose rather than turning knobs at random.

This is not a physics course, and you will not be asked to calculate anything. It is the working knowledge an operator-grade NCO needs to diagnose and fix "no comms" in the field: why VHF and UHF behave as line of sight, so terrain and antenna height decide their range far more than power does; how HF travels great distances by skipping off the ionosphere, and how NVIS reaches over hills that block VHF; what makes an antenna radiate well, and why a better, higher antenna usually beats more power and saves the battery; how to manage power against battery life; what limits and extends a Meshtastic mesh; and a simple, repeatable troubleshooting drill for the moment the net falls silent.

Treat this as the knowledge layer of the skill. The understanding is built here, online and at your own pace; the operating, raising a field antenna, working a repeater, reading why a link failed and fixing it, is practised and signed off in person and on airsoft milsim exercises, where real transmitting is done only by licensed members or on licence-free, low-power sets. By the end you will be able to explain why VHF and UHF are line of sight and why antenna height and high ground beat power for them; describe how HF skip and NVIS give long and regional reach with no infrastructure; state what makes an antenna effective and why a better antenna usually beats more power; manage radio power against battery life; explain what extends and limits a Meshtastic LoRa mesh; and run a disciplined "no comms" troubleshooting drill that finds the fault and gets the link back.

Key Terms

Propagation: how a radio signal travels from transmitting antenna to receiving antenna; the path it takes and what helps or stops it along the way.
Line of sight: the property of VHF and UHF that they travel essentially in straight lines and are blocked by terrain and obstacles, so the antennas must, roughly, be able to "see" each other.
VHF/UHF: the radio range above 50 MHz used for most local tactical voice; line of sight, worked either through a repeater or simplex.
Repeater: a station, usually high up, that receives on one frequency and re-transmits on another, extending the area two radios can cover by relaying for them.
Simplex: radio-to-radio direct, both stations on one frequency with no infrastructure; shorter range than a repeater but always available.
HF: the range 3 to 30 MHz that can travel far by refracting off the ionosphere (skywave or skip), giving regional and long-distance reach with no infrastructure.
Ionosphere: layers of charged particles high in the atmosphere that bend HF signals back toward the ground, letting them reach far beyond the horizon.
NVIS: near-vertical-incidence skywave; firing a lower-HF signal almost straight up so it comes back down across a wide region, covering ground behind hills that VHF cannot reach.
Antenna: the conductor that turns transmitter power into radio waves and receives them; a resonant antenna does this far better than a short stub.
Resonant antenna: an antenna cut to the right length for its frequency (a half-wave dipole, a quarter-wave ground plane, an end-fed wire) so it radiates efficiently.
Polarisation: the orientation of the radio wave, vertical or horizontal; antennas at both ends should match, and most tactical VHF is vertical.
LoRa / Meshtastic: a long-range, low-power digital bearer that carries tiny amounts of data on licence-free ISM bands, with nodes that relay (mesh) for each other to extend reach.
Squelch: the receiver control that mutes the speaker until a signal strong enough to want is present; set wrong, it either hisses constantly or hides weak callers.

Why VHF and UHF are line of sight, and what that means for you

Most of the section's voice traffic rides on VHF or UHF, the range above 50 MHz, and the single most useful fact about it is that it behaves essentially as line of sight. The waves travel in near-straight lines and are blocked by what gets in the way: hills, ridges, buildings, dense wet woodland, the curve of the earth itself over distance. Two radios that can, roughly, "see" each other will talk; two with a hill between them often will not, however good the kit. When a section loses VHF the cause is usually not a fault in a radio. It is terrain.

That single fact reorders your instincts. The untrained reach, when a signal is weak, is for the power switch, but for line-of-sight radio power is the weakest lever you have. The reason is geometry. What limits range is the horizon your antenna can see, and that horizon is set by height, not by how hard you push. Raise the antenna, or put it on higher ground, and you see further over the curve and over obstacles, and the range grows reliably. Double the transmit power and you gain only a little, because the obstacle that was blocking you is still there and the extra power does not bend around it. So the rule the section must drill into its bones is: height and high ground beat power. Before you turn anything up, ask whether you can get the antenna higher or move to better ground.

The two ways VHF covers ground are worth keeping distinct because they drive different choices in the PACE plan from Lesson 02. Simplex is radio to radio direct: both stations on one frequency, no infrastructure, always available, but range limited to what the two antennas can see between them. A repeater is a station, usually sited high on a hill or a mast, that listens on one frequency and re-transmits everything it hears on another. Because it is high, it can see a huge area, and any two radios that can each reach the repeater can therefore reach each other, even with a hill between them, because each is talking to the high station, not directly to the other. A repeater turns a line-of-sight problem into two shorter line-of-sight problems through a point that sees over everything. That is why a repeater is so often the Primary or Alternate for VHF voice and simplex the Contingency: the repeater gives reach, simplex gives independence when the repeater or its link is gone.

   VHF/UHF LINE OF SIGHT vs HF SKIP

   VHF/UHF (line of sight): the hill blocks it

     A )))            X            ((( B
      \             /====\             /
       \___________/ HILL \___________/
            no path: A and B cannot hear each other direct

   ...but a repeater on the hill sees both:

                 [ REPEATER ]
                 //         \\
     A ))) ------//           \\------ ((( B
      \_________//   HILL      \\_________/
        A reaches repeater; repeater relays to B

   HF SKIP (skywave): bounces off the ionosphere, over the hill

        . . . . . . IONOSPHERE . . . . . .
          \                          /
           \                        /
     A )))   \                      /   ((( C
      \_______\____/====\__________ /_______/
                    HILL        far away (regional / long range)

HF, the ionosphere, and NVIS: reaching where VHF cannot

When the distance is too great for line of sight, or terrain walls a region off from any repeater, the section turns to HF, the range from 3 to 30 MHz. HF can travel far because of the ionosphere, layers of charged particles high above the earth that act like a mirror for these frequencies. An HF signal fired toward the horizon climbs, the ionosphere bends it back down, and it returns to earth hundreds or thousands of kilometres away, well beyond the horizon and over every hill in between. This is skywave, or skip, and it needs no repeater, no mast, no infrastructure of any kind, only a radio, a wire antenna, and an ionosphere, which nature supplies. That independence is exactly why HF earns a place low in a PACE plan, as the means that still works when the masts and the mobile network are gone.

Skip has its quirks. The ionosphere changes with the time of day, the season, and the sun, so the frequency that reaches a given distance now may not reach it tonight; HF operators change band with conditions, and a signals NCO plans HF schedules expecting that. Skip also tends to overshoot: a signal aimed low at the horizon can fly clean over a nearer station and land far away, leaving a "skip zone" of silence in between.

The answer to that gap, and the HF technique most useful to a home-defence section, is NVIS, near-vertical-incidence skywave. Instead of aiming low at the horizon, you fire a lower-HF signal almost straight up, with a low horizontal antenna. The ionosphere bends it back down again, and it rains down across a wide circle, tens to a few hundred kilometres in every direction, including straight onto the ground behind the very hills that block VHF. NVIS fills in the regional coverage that line of sight cannot give and that ordinary skip flies over. For a force operating across broken ground with hills between its elements, NVIS on HF is often the means that reaches everyone at once, with nothing but a wire strung low between two supports.

What makes an antenna work, and why it beats power

If you take one practical lesson from the physics, take this: the antenna matters more than almost anything else you can change, and a better antenna usually beats more power while saving the battery. Understanding why lets you fix more "no comms" faults than any other single piece of knowledge.

An antenna turns transmitter power into radio waves on the way out and gathers waves into signal on the way in. How well it does this depends first on its length relative to the frequency. A resonant antenna, one cut to the right size for its band, a half-wave dipole, a quarter-wave ground plane, an end-fed wire, radiates efficiently: most of the power you feed it leaves as useful signal. The stubby rubber antenna fitted to a handheld for convenience is a compromise, far shorter than resonant, and it throws away much of your power as heat. Swapping that stub for a proper resonant antenna can do more for your range than any amount of turning up the power, because it stops wasting what you already have.

Three things govern an antenna's performance in the field, and you control all three. Height is first, especially on VHF and UHF: an antenna up a tree or on a mast sees further and clears obstacles, for the same line-of-sight reason as before. A clear path is second: get the antenna out from behind the metal of a vehicle, off the wet ground, away from the wall or the dense canopy that absorbs the signal; even a metre into the clear can transform a link. Matching polarisation is third: a radio wave has an orientation, vertical or horizontal, and the antennas at both ends should match. Most tactical VHF is vertical, so a vertical whip talks to a vertical whip; hold one sideways and you lose signal for no reason but geometry. Get height, a clear path, and matching polarisation right and a modest radio reaches far; get them wrong and the strongest radio in the section struggles.

This is why a better, higher antenna usually beats more power, and the battery benefit is not a side note but a reason in itself. More power drains the battery faster for only a small gain in range. A better antenna costs no battery at all: it makes the power you are already spending count for more. In a force that may be out for a long time on what it can carry, the antenna that lets you use less power to reach further is worth more than the loudest radio.

   ANTENNA HEIGHT vs RANGE (the higher antenna sees further)

   range
     ^                                   antenna on the mast
     |                          ____.----'  reaches far
     |                 ____.----'
     |        ____.----'   antenna on the hand (low) reaches less
     |   .----'________________________
     +------------------------------------------> antenna height
       low                              high

   Same radio, same power. Raising the antenna does more
   than turning up the power. And height costs no battery.

Power and battery: a flat radio is no radio

Power deserves its own short word, because the instinct to reach for it is so strong and so often wrong. The honest figure is this: doubling your transmit power buys only a small increase in range, because range on line-of-sight radio is ruled by the horizon and on HF by the ionosphere, and power changes neither much. You spend a great deal of battery for a little reach.

Against that small gain sits a hard cost. A flat radio is no radio, and a section whose sets die mid-task has lost its comms as surely as if every antenna had snapped. So the signals NCO manages power as a resource, not a reflex. Run on low power by default and step up only when a link genuinely needs it, and only after height, antenna, and position have been tried. Plan battery life into the task: know how long the sets last at the power you are using, carry or stage spares, and track every radio's charge the way you track ammunition or water. The discipline pairs with the antenna lesson: because a better, higher antenna reaches the same distance on less power, good antenna work is also good battery work. Together they are how a small force stays on the air for long.

Meshtastic and LoRa: range, terrain, and the mesh

The section's digital bearer, the one that carries position reports and short text where the voice net cannot reach and where there is no mobile data, is Meshtastic running on LoRa. It is worth understanding plainly, because its strengths and its hard limits both shape how you use it.

LoRa is a long-range, low-power technique on licence-free ISM bands, which is what lets the section use it on exercise without every member holding an amateur licence. It achieves its range by sending tiny amounts of data very robustly, spread out so a weak signal still gets through. The price is bandwidth: LoRa carries position pings and short text and nothing more. It is not for voice, not for files, not for pictures. Treat it as a thin, tough thread for the lightest traffic, position and a few words, and never ask it to carry what it cannot.

Its range obeys the same physics as everything else here. It is helped by height, hurt by terrain, and lives or dies by the antenna, exactly as VHF does; a node low behind a hill reaches little, the same node lifted onto high ground reaches far. What makes Meshtastic valuable is the mesh: nodes relay for each other. A message that cannot reach its destination directly hops node to node, so the network as a whole reaches much further than any single node could, with no infrastructure at all. A well-placed high node can knit a whole section's mesh together by relaying for everyone, the same way a repeater serves a VHF net. So when you plan or fix a mesh, think as you would for VHF: get nodes high, give them a clear path and a decent antenna, and position one to relay for the rest. The mesh extends reach, but only across links the physics will actually carry.

A "no comms" troubleshooting drill

When the net goes quiet, the difference between a trained signals NCO and an anxious one is a drill. Do not turn knobs at random and do not declare the link dead. Work a fixed checklist, simplest and most likely first, changing one thing at a time so you learn what the fault was. The order below moves from "is the radio even working" out to "is the path even possible," which is the order in which faults are both most common and quickest to fix.

   "NO COMMS" TROUBLESHOOTING DRILL  (work top to bottom)

   1. POWER / BATTERY ...... Is it on? Battery charged / seated?
        |                    Swap battery if in doubt.
        v
   2. VOLUME / SQUELCH ..... Volume up? Squelch set right?
        |                    (Too tight hides weak callers;
        |                     too loose buries them in hiss.)
        v
   3. FREQUENCY / CHANNEL .. Right channel? Same as the others?
        |                    Repeater vs simplex correct?
        v
   4. ANTENNA / CONNECTION . Antenna fitted, screwed tight, not
        |                    cracked? Right antenna for the band?
        v
   5. POSITION ............. Still nothing? The PATH is the fault.
        |                       - MOVE off the dead spot
        |                       - GET HEIGHT (high ground / mast)
        |                       - try a RELAY (repeater, another
        v                         station, a high mesh node)
   LINK RESTORED  ->  log the cause; tell the net.

   One change at a time. Most faults die at steps 1-4.

Walk the steps. Power and battery first, because a flat or unseated battery is the commonest fault of all and the fastest to fix; if in doubt, swap the battery. Volume and squelch next: a volume turned down or a squelch set too tight will hide a caller who is actually getting through, and these cost nothing to check. Frequency and channel third: confirm you are on the right channel and the same one as the rest of the net, and that you are set for repeater or simplex as the plan requires, a wrong channel mimics a dead link perfectly. Antenna and its connection fourth: make sure the antenna is fitted, screwed down tight, not cracked or swapped for the wrong one, because a loose or wrong antenna wastes the signal you are paying battery for. Only when all four pass do you conclude the fault is the path itself, and now the physics of this lesson tells you what to do: move off the dead spot, get height onto better ground or up a mast, or bring in a relay, a repeater, another station, or a high mesh node, to bridge the obstacle. Run the drill the same way every time, change one thing at a time so you know what fixed it, and log the cause when you find it, because a fault that beat you once will teach the section how to avoid it next time.

In Practice: A Corporal Gets the Section Back on the Net

A section of the Royal Kaharagian Army is on a humanitarian exercise across broken ground, two detachments working either side of a wooded ridge, the Corporal who leads the section running comms for both. The PACE plan from Lesson 02 reads: Primary, TAK over mobile data; Alternate, VHF voice through the hill repeater; Contingency, VHF simplex; Emergency, Meshtastic text. The communications check before the move was clean on every link.

An hour in, the far detachment goes quiet on VHF. The Corporal does not reach for the power switch and does not panic the net. They run the drill. Power and battery: their own set is fine, charge good. Volume and squelch: both correct. Frequency and channel: they are on the repeater channel, correct, and the far detachment confirmed it earlier. Antenna and connection: their whip is tight and vertical. Four steps pass, so the fault is the path. The Corporal pictures the ground: the far detachment has moved down into dead ground behind the ridge, out of sight of the repeater on the hill, and VHF cannot bend around it. This is not a radio fault; it is line of sight doing exactly what line of sight does.

So the Corporal works the physics. First they call the far detachment to get height, move to the shoulder of the ridge where the repeater can be seen, and the link returns at once, height beating everything. But the detachment's task keeps it low for now, so the Corporal sets a longer fix in line with the lesson: they raise the far detachment's antenna on a short mast for a clearer path, and they drop down the PACE plan to the Emergency means deliberately, bringing up Meshtastic, which relays across the mesh and carries the detachment's position reports through a high relay node even while the voice link is blocked. Position keeps flowing on the thin tough thread while voice is restored. No power was turned up, no battery wasted, no link declared dead. The Corporal found the fault by drill, named it as terrain, and beat it with height, a better antenna, and a relay, then logged the cause so the section would read that ground correctly next time. That is the whole of this lesson at work.

Check Your Understanding

Explain why VHF and UHF behave as line of sight, and why this means antenna height and high ground extend their range more reliably than power does. Then distinguish a repeater from simplex, and explain why a repeater can connect two radios that have a hill between them when simplex cannot.
Describe how HF travels far by skywave off the ionosphere, and explain what NVIS is and why it reaches a region behind hills that both VHF and ordinary HF skip would miss. Why does HF earn a place low in a PACE plan even though it is slower and more variable than VHF?
State the three things that govern an antenna's performance in the field, and explain why a better, higher antenna usually beats more power and saves the battery. Then list, in order, the steps of the "no comms" troubleshooting drill, and explain why you change one thing at a time.

Reflection (write a short paragraph): This lesson argues that the trained instinct, when a link is weak, should be the opposite of the untrained one: reach for height, antenna, and position before you reach for power. Think about how you would actually behave the first time a net went quiet under stress with people relying on you. Be honest about whether your reflex would be to turn the power up and hope, or to work the drill calmly from the top. What is one habit, in how you set up, check, or think about a link, that you could start building now so that the disciplined response becomes the automatic one when it matters? Consider too what you would teach your operators first, given that you will train them as well as lead them.

Summary

VHF and UHF are essentially line of sight: terrain and obstacles block them, and range is set by antenna height, not power. Height and high ground beat power, and they cost no battery, so reach for them first. A repeater on high ground relays for two radios that cannot see each other directly; simplex is radio to radio direct, shorter but always available. These map onto the Alternate and Contingency means of the PACE plan from Lesson 02.
HF travels far by skywave, refracting off the ionosphere with no infrastructure, which earns it a low place in a PACE plan as the means that survives when masts and mobile data are gone. Its conditions vary with day, season, and sun, and skip can overshoot nearer stations. NVIS fires a lower-HF signal almost straight up to rain coverage across a region, including the ground behind hills that VHF cannot reach.
An antenna matters more than almost anything else you can change. A resonant antenna (dipole, ground plane, end-fed wire) radiates far better than a short stub. Height, a clear path, and matching polarisation, most tactical VHF being vertical, govern its performance. A better, higher antenna usually beats more power and saves the battery, which is also good battery discipline.
Doubling power buys only a small range gain for a large battery cost, and a flat radio is no radio. Manage power as a resource: run low by default, step up only after height, antenna, and position have been tried, and track every set's charge like ammunition. Meshtastic on LoRa carries only tiny data (position and short text), obeys the same physics of height, terrain, and antenna, and extends reach by meshing, nodes relaying for each other, with a high node serving the mesh as a repeater serves a voice net.
When the net goes quiet, run the "no comms" drill in order, power/battery, volume/squelch, frequency/channel, antenna/connection, then position (move, get height, or relay), changing one thing at a time and logging the cause. This lesson supplies the physical understanding behind the planning of Lesson 02 (Communications Planning and the PACE Plan) and the net management of Lesson 04 (Running the Net and the Detachment). It builds on the operator-level signals knowledge of SIG 201 and SIG 220 and the field signals awareness of FLD 220, and supports Patrolling FLD 230, Navigation FLD 201, Emergency Preparedness HCR 220, and the signals paragraph of orders in PME 210.

Antennas, Propagation, and Getting Through