Radio propagation field manual

Start with the actual job

Before looking at solar flux, a waterfall, or a row of cheerful green boxes, define the path. Who needs to reach whom? From where? How far apart are they? Is the receiving station fixed, mobile, portable, on the other side of a ridge, in another state, aboard a vessel, or moving down a corridor? The correct propagation question for a two-mile simplex call is not the correct question for a 150-mile regional path, and neither has much to do with a 4,000-mile HF contact.

For Team Stone, the useful categories are ordinary local VHF/UHF, repeater or linked-node access, regional HF/NVIS, ordinary HF skywave, DX, marine paths, and satellite paths. Each has a different failure mode. Local VHF usually loses to terrain, antenna height, polarization, or a bad installation. Regional HF can lose because the chosen frequency is above the useful near-vertical critical frequency or below the practical LUF. DX can vanish because the MUF fell, D-region absorption rose, the path moved into darkness, or a geomagnetic disturbance made the whole forecast academic. Satellite work loses when the spacecraft is not where the operator hoped it was, which is at least refreshingly honest.

HF without the incense

The ionosphere is a set of ionized regions whose density and height change with solar illumination, season, solar activity, geomagnetic disturbance, latitude, and time. The D region is primarily important to an HF operator because it absorbs lower-frequency energy during daylight. The E region can support ordinary and sporadic-E paths. The F region, particularly F2, carries much of the long-distance HF work. At night the D region largely collapses and the F1/F2 structure changes, often improving the lower HF bands even while the upper bands close.

That is why the same station can find 10 meters excellent in the afternoon and nearly unusable after dark, while 40 or 80 meters improves. The radio did not change. The antenna did not change. The circuit changed because the ionosphere is part of the circuit.

MUF, LUF, foF2, and why the words matter

The maximum usable frequency is path-specific. Above the MUF for a particular path, ordinary ionospheric refraction will not return the signal to the intended receiving area. The lowest usable frequency is practical rather than ceremonial: absorption, noise, transmitter power, antenna gain, mode, and receiver performance decide whether the signal rises above the noise. When the LUF rises above the MUF, ordinary HF skywave for that path has no useful frequency window. That is not a request for more optimism.

foF2 is the vertical critical frequency measured or inferred from ionosonde data. It becomes particularly useful for NVIS because the desired ray is deliberately steep. If the operating frequency is too high for the current vertical path, the signal can sail through the layer and create a skip zone exactly where the operator wanted regional coverage. Current ionosonde and MUF maps are therefore much more useful than a laminated rule that says “40 meters in the day, 80 at night” as if the atmosphere signed the card.

NVIS: regional coverage on purpose

Near Vertical Incidence Skywave is not failed DX. It is a deliberate regional technique. A relatively low horizontal antenna favors high-angle radiation; the ionosphere returns that energy to cover distances that may be awkward for VHF repeaters and too short for a conventional low-angle HF hop. In California and the Pacific Northwest, that matters because mountains and long valleys can make a short map distance a terrible line-of-sight path.

The practical Team Stone approach is to test 80 and 40 meters rather than canonize either one. Use the current ionospheric state, time of day, noise floor, and the receiving station to decide. If 40 is above the useful vertical critical frequency, move lower. If 80 is being mauled by daytime absorption and noise, try 40. Log what actually worked. The point of doctrine is to turn repeated experience into a faster decision next time.

Solar flux, Kp, A, and NOAA's G/R/S scales

Solar flux at 10.7 cm and sunspot number are broad indicators of solar activity. Sustained higher activity often supports higher HF maximum usable frequencies, which is why 10, 12, 15, and 17 meters can become dramatically more productive around strong portions of the solar cycle. They are not path predictions by themselves.

Kp is a three-hour planetary geomagnetic disturbance index; A or Ap summarizes disturbance over a longer period. Low, steady geomagnetic activity is usually friendlier to ordinary HF, especially high-latitude paths. NOAA's G scale describes geomagnetic storms, the R scale describes solar-flare radio blackouts, and the S scale describes solar radiation storms. The distinction matters. An R-scale event can degrade or black out HF on the sunlit side very quickly. A G-scale storm can disturb HF and GNSS differently and over a longer interval. If several HF bands collapse at once, check space weather before dismantling the antenna farm in a fit of character-building.

Day, night, sunrise, and sunset

Daylight increases ionization and D-region absorption at the same time. Higher HF bands often benefit from the added ionization while lower HF pays the absorption bill. After sunset the D region fades quickly while the F region persists, so lower bands can improve even as upper bands close. Around sunrise and sunset, the changing conditions along a long path can create useful transitions. Gray-line maps are worth checking, but they are a clue, not a reservation.

For field work, think about illumination along the entire path rather than only at the transmitting station. A path from California to the eastern United States, Europe, Alaska, or the Pacific is moving through different local times. A band that is dead in one direction may be excellent in another because the path is not the same circuit.

VHF, UHF, and six meters

For normal 2-meter and 70-centimeter FM/C4FM, terrain and antenna geometry dominate. Antenna height, ridge clearance, polarization, feed-line loss, vehicle body shielding, and receiver desense are usually more important than the solar flux number. The radio horizon is somewhat beyond the geometric horizon because of normal atmospheric refraction, but no atmospheric footnote makes a mountain transparent.

Six meters is the interesting border country. F2 can support long paths during strong solar conditions; sporadic-E can produce abrupt, intense openings with very little warning; and tropospheric enhancement can extend VHF paths under favorable atmospheric layering. On 2 meters and above, tropospheric ducting, meteor scatter, auroral propagation, aircraft scatter, and EME all exist, but they are specialized paths. For an ordinary field station, the first VHF fix remains gloriously unromantic: get the antenna higher, clearer, and better coupled to the radio.

Terrain can beat watts

Moving fifty yards can change a VHF path. So can stepping out from behind a vehicle, moving from the lee side to the shoulder of a ridge, getting the handheld above head height, or moving the mobile antenna from glass to a proper exterior mount. The same five-watt handheld can be a completely different station depending on whether its antenna is below a metal roofline or standing in the clear.

This is why RepeaterBook belongs in the field kit. It is not a propagation predictor, but it answers a practical propagation question: what infrastructure is actually nearby, at what site, on what band, and with what access parameters? Its offline database is especially valuable after leaving cell coverage. myGMRS serves the same discovery role for licensed GMRS operation, subject to repeater-owner access terms and current status.

Noise floor: the propagation problem inside the house

A perfectly adequate signal can arrive at the antenna and still be unusable because the local noise floor is high. Switching power supplies, chargers, LED lighting, Ethernet, computers, solar electronics, appliances, and common-mode current on feed lines can raise the receiving floor by many decibels. From the operator's perspective, reducing that noise is equivalent to improving the path because it changes what can actually be copied.

That is why the station-engineering material belongs beside propagation. Common-mode control, feed-line integrity, bonding, and RFI work directly affect the usable receiving system. A quieter station can outperform a louder transmitter because communications is a two-way exercise, a detail sometimes omitted by people who own amplifiers.

Satellites and packet from above

Satellite propagation is geometry plus spacecraft status. The satellite has to be above the usable horizon, the radio has to be on the correct uplink/downlink or packet frequency, Doppler may matter, and the payload has to be operating in the expected mode. For Team Stone, satellite APRS is especially valuable because a successful packet can move position/status/message traffic far beyond terrestrial repeater coverage. ISS APRS on 145.825 MHz remains the durable reference memory, but the live ARISS/AMSAT status must be checked before relying on any particular pass.

The field tools that earn their space

HamLog also carries band plans, grid and bearing tools, wavelength calculations, WWV propagation information, DX spotting/cluster access, DTMF generation, UTC, callsign lookup and quick ADIF/CSV logging. That makes it one of the few apps that can answer several different field questions without sending the operator on a scavenger hunt through twelve websites.

WSPR Watch and live digital activity provide evidence about weak-signal paths. RepeaterBook gives the local infrastructure picture and can retain its database offline. myGMRS does the same sort of discovery for GMRS. WiresApps can refresh its local active-node database from Yaesu and then locate nearby WIRES-X nodes quickly; the FT-5DR still makes the RF connection. MSeven - M17 gives iOS a current M17 client. QSO One will become much more important to the iPhone field stack when its iOS client actually ships; until then, it remains a Windows path for this station rather than something we pretend exists because a roadmap is emotionally satisfying.

A five-minute propagation decision

1. Define the destination, distance, and required reliability.
2. Classify the path: local line-of-sight, repeater/node, regional NVIS, ordinary HF skywave, DX, marine, or satellite.
3. Check terrain and antenna geometry before touching the power control.
4. For HF, check current space-weather warnings and a current MUF/foF2 or path product.
5. Listen. Use WSPR/FT8/beacons/nets/broadcast signals as evidence.
6. Try the most likely band, then an adjacent sensible band rather than repeating the same failed call louder.
7. Log what worked. The next decision should be faster because this one happened.

Primary live references