Tactical radio troubleshooting

What to check when the radio will not talk, in the order that rules out the most causes fastest, and why each check matters. Written for anyone who has to make a net work — not only for signal soldiers.

What this is, and what it is not

This page is general guidance, assembled from Army doctrine, standard radio-wave and antenna fundamentals, and manufacturer information that is published openly. It gets you through the faults that cause most lost comms, which are almost never the radio itself.

It is not a substitute for your equipment's technical manual. Set-specific procedures — menu paths, error codes, fill steps, maintenance actions — live in the TMs and field reference guides, most of which carry distribution or export-control restrictions and are therefore not reproduced here. Where a step needs one, it is named so you can pull the copy your unit already holds. Anything to do with keys, frequencies or your unit's actual net data belongs on your network, not on a public page.

Start here

The first five, in this order

Power. A charged battery of the right type, seated and latched. On a vehicle set, the platform's power on and the mount actually powering the radio. Most "dead radio" calls end here.
Antenna and connections. The right antenna for the band, fully seated, and the cable undamaged. A whip that is loose, a coax with a crushed shield or a connector spun finger-tight will pass a visual check and still kill a net.
The net data matches. Same frequency or preset, same mode, same net ID, same waveform, same bandwidth, same squelch. One radio on a different preset than everyone else is the single most common cause of "my radio is broken".
Keys and time. The right key in the right slot, still inside its crypto period, and the radio's time close enough to the net's. Frequency-hopping and most modern waveforms will not pass traffic if either is wrong.
Where you are standing. Terrain, antenna height and how far away the other station is. Half of all "no comms" reports are a radio working exactly as designed in a place it cannot reach from.

Work top to bottom and change one thing at a time. Two changes at once means that when it starts working you have learned nothing, and the fault comes back tomorrow.

What is it doing?

Radio reference

Ranges, waveform families and what each set pairs with — enough to know what you are holding and what it should be able to do. Procedures are in each set's TM.

Reference

Everything that has to match, end to end

If one station cannot talk to the net, this is the list to walk. If nobody can talk to anybody, suspect the plan rather than the radios.

Setting	What goes wrong
Frequency / channel / preset	One station on the wrong preset, or on the training net from last week.
Mode (single channel vs frequency hopping)	A single-channel radio cannot hear a hopping net at all, and vice versa.
Waveform	Two radios that both cover the band still cannot talk if one is on SINCGARS and the other on a wideband waveform.
Net ID / hopset / TSK	Right band, right mode, wrong net: silence, or you hear one side only.
COMSEC key and slot	Cipher text on one end and plain text on the other gives noise, not words.
Time of day	Hopping and time-synchronised waveforms will not sync outside their tolerance.
Bandwidth / channel spacing	25 kHz against 12.5 kHz, or a wideband channel plan against a narrowband one.
Squelch type and tone	You transmit fine and nobody's squelch opens, so nobody answers.
Power level and antenna	Low power into the wrong antenna reaches nobody; high power into a bad load can damage the set.
Crypto mode / traffic type	Digital voice at one rate against another is intelligible to neither.

Frequency-hopping vocabulary

Worth knowing because the words are used loosely, and the fault is usually in exactly one of them.

Hopset — the list of frequencies the net hops across.
TSK — transmission security key; it drives the hopping pattern.
ESET — hopset plus TSK.
COMSEC key — the traffic encryption key that protects what is said.
LOADSET — ESET plus COMSEC.
Net ID — the start point along the hopset; it is what separates one net from another on the same hopset.
FHM — the frequency hopping master, the net control station that holds net time.

On SINCGARS, every station in a hopping net needs the same traffic encryption key and the same hopset, and must be within about four seconds of net time. Late net entry from the FHM is the normal fix for a station that has drifted.

Antenna quick math and siting

Resonant wire length in feet: 936 / f for a full wave, 468 / f for a half wave, 234 / f for a quarter wave, with f in MHz.
Vertical polarisation favours ground wave; horizontal favours skywave. Sky waves arrive elliptically polarised. Mismatched polarisation between two stations costs signal for nothing.
The longest antenna the situation allows performs best. Most Army field antennas are non-resonant, which is why they work across a band rather than at one frequency.
A radiation resistance at or above about 50 ohms makes ohmic losses unimportant; below that, losses start to matter. A half-wave antenna in the clear is about 73 ohms.
For HF over short ranges, near vertical incidence skywave puts the signal up and back down inside the terrain that blocks ground wave. The AS-2259/GR is the field NVIS antenna: crossed sloping dipoles on a 15-foot mast, 2 to 30 MHz, omnidirectional in azimuth.
Site selection is really take-off angle selection: obstacles near the antenna raise the angle your signal has to leave at, and for a 30-foot antenna a 5 degree take-off angle wants roughly 2 km of clearance to the treeline, against about 300 m at 30 degrees.

Choosing an HF frequency: time of day and distance

HF is the band that punishes guesswork and rewards a plan. Three numbers bound every circuit.

MUF, the maximum usable frequency — above it the wave passes through the ionosphere and is lost. It is highest around local noon, when the sun's ultraviolet is most intense, and falls sharply afterwards.
LUF, the lowest usable frequency — below it the signal is absorbed and buried in noise.
FOT, the frequency of optimum transmission, roughly 85% of the MUF — the practical working frequency, because neither boundary is a place to operate. At the LUF the signal-to-noise ratio is poor and multipath is likely; at the MUF, ordinary ionospheric variation drops the circuit.

Why the same frequency stops working after dark. The ionised layers are made by sunlight, so they move and change through the day. At night the F1 and F2 layers combine into one, and a frequency that worked at noon can be unusable at midnight — and the other way round. Plan a day frequency and a night frequency; do not plan one and hope.

Band	What it is good for
2 - 5 MHz	Short and intermediate range skywave in daylight; good long range at night.
5 - 10 MHz	Similar, with long range possible in daylight under good conditions.
10 - 15 MHz	The most reliable intermediate and long range band across conditions.
15 - 25 MHz	Short range by surface wave on a whip; long range highly variable and condition-dependent.
25 - 30 MHz	Very short range, and excellent long range when conditions are good.

Space weather sets what is possible on the day: current solar flux and the A and K indices are the inputs a prediction depends on, and a point-to-point VOACAP prediction turns them into which frequency will hold for your circuit, hour by hour. A geomagnetic disturbance will take an HF circuit away from you whatever the radio is doing.

Picking an antenna by the distance you need

Distance	What usually works	What to watch
Within a few km	Handheld or vehicle whip on VHF or UHF.	Terrain and buildings, not power. Get height before you raise power.
Out to the radio horizon	Vehicle whip, or a field antenna up a mast on the combat net.	Antenna height is the lever that matters. Vertical at both ends.
Beyond line of sight, short	HF near vertical incidence, or a retrans.	NVIS wants a horizontal antenna low to the ground and a low-ish frequency; a vertical whip throws the energy at the horizon instead.
Hundreds of km	HF skywave at or near the FOT, with a low take-off angle.	Site for clearance toward the distant station; obstacles near the antenna raise the take-off angle and shorten the hop.
Any distance, on demand	UHF TACSAT or MUOS.	Needs an access authorisation, the right satellite antenna, and a clear view in the right direction.

The rule underneath the table: the longest antenna the situation allows, as high as you can put it, polarised to match the other station. That beats a power setting almost every time, and it costs no battery.

Siting a retrans, step by step

Work out what the site has to see. A retrans is chosen for what it can reach on both halves of the net, not for where it is convenient to park. Plot both subscriber groups first, then look for ground that sees both.
Pick a primary and at least one alternate. Plot both on the course of action sketch, with the criteria for moving between them known to everyone before anybody deploys.
Get the frequencies deconflicted. More separation between the two nets means the antennas interfere with each other less, so the frequency plan and the site plan are the same problem.
Separate the antennas. 10 to 15 feet horizontally and 10 feet vertically as a floor, and more as power or antenna gain goes up. Cross the polarisation and put terrain or a shield between them where you can.
Test for self-interference before you rely on it. Key one side and listen on the other. A site that jams itself desensitises its own receiver and produces faults that look like broken radios, days later and miles away.
Make the team self-sufficient. Two antennas per planned net with all cables, spare radios and batteries, a fill device, a GPS receiver, a radio test set, and power for the duration.
Rehearse and set the reporting. A pre-combat checklist, a rehearsal, and a reporting schedule back to the establishing headquarters — so that a site going quiet is noticed as a fault rather than assumed to be silence.
Write down the configuration. Antenna heights, separation, polarisation and frequencies. The next team, or the same team at the alternate site, starts from what worked.

Retransmission sites

Separate the two antennas: at least 10 to 15 feet horizontally and 10 feet vertically as a floor, and more when power or antenna gain goes up.
Too little separation desensitises the receiver, distorts the signal and generates spurious signals — the site jams itself, and the symptom looks like a broken radio.
More frequency separation between the two nets makes physical separation less critical. Crossing polarisation — one vertical, one horizontal — helps significantly, and a physical shield between them helps further.
The four types are single channel to single channel, single channel to frequency hopping, FH1 to FH1, and FH1 to FH2.
A retrans team leaves with what it needs to work alone: two antennas per planned net with all cables, spare radios and batteries, a fill device, a GPS receiver, a radio test set, and the pre-combat checklist it rehearsed against.

Interference and suspected jamming

Interference you cause yourself is far more common than interference an enemy causes you: a second radio too close, a generator, a vehicle ignition, a nearby transmitter on an adjacent frequency, or a retrans site with its antennas too close together. Prove those first.

The classic test is to disconnect the antenna. If the noise disappears, it is arriving through the antenna and is external. If it stays, the trouble is inside your own set or its power.

If you do believe you are being jammed: do not stop transmitting to see if it stops, and do not talk about it on the affected net. Continue to operate, work through it, and report it — the MIJI report is the format for suspected jamming and for interference you cannot identify. Changing frequency to escape is a short-term fix; the report is what gets it resolved. ATP 6-02.72 carries the full range of interference resolution techniques, and electromagnetic warfare and spectrum staff officers exist to help diagnose it.

What to tell the S6 or the net control station

A fault report that contains these answers gets fixed on the first call back. One that does not costs an hour of twenty questions.

Radio type and mount, and whether it is dismounted or on a platform.
Which net, which preset, and which waveform and mode.
What it is doing exactly: nothing heard, heard but not answered, garbled, drops after a minute.
Who else on the net has the problem — one station, or everyone.
When it started, and what changed just before (new fill, new position, new antenna, vehicle moved).
Which of the first five you have already checked, and what you saw.
Your location and antenna setup, and the distance to the station you cannot reach.
Key and fill status: which key, loaded when, and whether the fill device has been verified against another radio.

Where the authority actually is

FM 6-02, Signal Support to Operations — how signal support is organised and planned.
ATP 6-02.53, Techniques for Tactical Radio Operations — the doctrinal reference for operating tactical radio nets.
ATP 6-02.72 — interference resolution and operating through jamming.
ATP 6-02.75, Techniques for COMSEC Operations — keys, fills and their handling.
TC 9-64, Communications-Electronics Fundamentals: Wave Propagation, Transmission Lines, and Antennas — the antenna and propagation fundamentals behind half this page.
TB 11-5820-1141-10 — the HF near vertical incidence skywave antenna handbook.
Your set's operator TM and the manufacturer's field reference guide, for anything specific to the radio in your hands.

About the sources

The fundamentals here come from Army doctrine and from standard propagation and antenna theory, both of which are published openly. Set nomenclature, frequency coverage and waveform lists come from manufacturer material released as non-export-controlled, and from the equipment's own published designations.

Deliberately absent: anything drawn from technical manuals and vendor documentation that carry distribution or export-control statements. Those are cited by number where they are the right place to look, and not quoted. If a procedure you need is not here, that is why — it is in the TM.