Radio takes the same electromagnetic wave that Signal Processing treats in the abstract and that Radar bounces off a target, and instead carries it one way, transmitter to receiver, as information. 37 articles and seven three.js microsims trace that path: the spectrum a wave lives in, how it propagates, the antenna that sends and catches it, the transmission line and receiver behind the antenna, and the modulation that puts something on the carrier in the first place. Article face: [[Radio]]. Sibling spine [[PORTAL_Signal_Processing]] supplies the sampling, filtering and transform machinery in the abstract; sibling spine [[PORTAL_Radar]] shares this portal's own antenna and propagation physics — literally the same `wt-radio.js` library — but reads a reflected echo instead of a cooperative transmission. The physics here is closed-form throughout, nothing baked, computed fresh on every control change from `wt-radio.js`'s `prop`, `ant`, `line`, `rx` and `spectrum` namespaces, plus `wt-signal.js`'s `mod`/`lti` for the one sim — [[Single-sideband_modulation]] — that needs them. ## Microsims — three.js (built, gate-verified — awaiting deploy) Seven root sims for the portal pack (`specs/portals/PORTAL_Radio.pack.json`, `BRIEFS_radio.md`: 7 roots). All seven are built and gate-verified (SHIP) in the working tree; none are live yet on the production Netlify site, so — the same honesty rule as Signal Processing's own build-target row — this table carries the real explanatory text a live embed would otherwise carry, not an iframe. Intended path once deployed: `https://wikitube-3d-microsims.netlify.app/radio/<slug>.html`. | # | Station | Concept | Explanatory text | Try | |---|---------|---------|-------------------|-----| | 1 | [[Radio_spectrum]] | ITU bands vs. IEEE radar letters | A 3D shelf of colour-coded band blocks runs along a single log-frequency axis (3 Hz to 3 THz), with a movable frequency marker and a toggle between the ITU's twelve decade bands and the IEEE's incompatible radar-letter bands, which cover the same frequencies under different names. At 2.45 GHz, ITU calls it UHF while IEEE calls it S band — both correct, different books. | Switch schemes at a fixed frequency and watch which name changes. | | 2 | [[Multipath_propagation]] | Two-ray fading and the break distance | A 3D ground-plane scene — transmit mast, receive antenna, a direct ray and a ground-bounce ray — sits beside a received-power-vs-distance chart. The two copies of the signal add and cancel as the receiver moves, reinforcing up to +6 dB or cancelling in deep nulls, until a break distance beyond which the field settles into a steady 40 dB/decade roll-off; at the break distance the two-ray loss is exactly 6.02 dB better than free space (a constructive peak), and at half that distance, 34.7 dB worse (a deep null). | Drag distance out to the break point and past it, and watch the oscillation give way to a smooth curve. | | 3 | [[Free-space_path_loss]] | Path loss as a power waterfall | A single vertical waterfall/bridge bar chart in dB steps transmit power up by the antenna gains and down by the path loss, landing on received power against a sensitivity threshold. Even with nothing in the way, received power falls off purely from geometric spreading — every doubling of distance or frequency costs exactly 6.02 dB; at 10 km / 2.4 GHz the loss is 120.05 dB and the margin is +14.94 dB (the link closes), but at 100 km the same link's margin flips to -5.06 dB (it fails). | Drag distance out until the margin bar flips from green to red. | | 4 | [[Antenna_(radio)]] | Radiation patterns as 3D lobes | A single translucent radiation-pattern lobe — dipole, monopole, loop or Yagi, selectable — orbits in 3D, with a ground plane under the monopole case and a linear/dB view toggle. An antenna's radiation pattern is a 3D lobe shape, and directivity is that lobe's shape read as one number: a half-wave dipole's directivity is 1.641 (2.15 dBi), and a quarter-wave monopole is exactly double that, because all the power stays above the ground plane. | Switch to Yagi and add directors, watching directivity climb and the back lobe shrink. | | 5 | [[Standing_wave_ratio]] | Mismatch, reflection and VSWR | The standing-wave envelope along a transmission line is plotted beside a Smith-circle inset showing the reflection coefficient. A mismatched load reflects part of the incident wave, and the resulting pattern's peak-to-trough ratio (VSWR) is a direct, single-number measure of how bad the mismatch is — 1 for a perfect match, unbounded as the load approaches a short or an open; a 100 ohm load on a 50 ohm line gives Gamma = 0.333 and VSWR = 2.000 exactly, matching the scanned envelope's own max/min ratio. | Push the load toward a short or an open and watch VSWR climb without bound. | | 6 | [[Crystal_radio]] | Tuned-circuit selectivity, no amplifier | Two stacked frames show a detector's time-domain trace with the true envelope ghosted behind it, and the tuned circuit's selectivity curve. A crystal radio has no amplifier: an LC tuned circuit rejects unwanted stations, fighting the load placed on it, and a diode-plus-RC envelope detector follows the AM envelope provided its time constant is neither too short (ripple leaks through) nor too long (it can't follow the envelope back down — diagonal clipping); at 1 MHz tuning, a loading of 5,000 ohm gives only 0 dB rejection of a station 10 kHz away, but 100,000 ohm gives -20.1 dB. | Raise the loading resistance and watch the next-door station get rejected. | | 7 | [[Single-sideband_modulation]] | Cutting AM down to one sideband | Two stacked frames show spectral stem lines with a bandpass filter's response overlaid. Ordinary AM wastes power on a carrier and a redundant mirror sideband; SSB strips both, transmitting only the information-bearing half at the cost of needing a very sharp filter — at fc = 4 MHz, fm = 1 kHz, AM totals 1.245 units of relative power against USB's single line at 0.25 (a 6.97 dB saving), and even an extreme filter Q of 50,000 only reaches 31.9/37.9 dB of carrier/image suppression, showing why real SSB filters need many more poles than a simple LC tank. | Switch through AM / DSB-SC / USB / LSB and watch the spectrum shrink. | ## Child articles All 37 are written and gate-verified at wt-article density, grouped below by the spine's own five parts. ### Part A — Waves and the spectrum - [[Radio]] — use of radio waves for communication; the hub article - [[Radio_wave]] — type of electromagnetic radiation - [[Radio_spectrum]] — electromagnetic spectrum, 3 Hz – 3000 GHz *(sim above)* - [[Very_high_frequency]] — electromagnetic wave range of 30–300 MHz - [[Ultra_high_frequency]] — electromagnetic spectrum 300–3000 MHz - [[Shortwave_radio]] — radio transmissions using wavelengths between 10 m and 100 m - [[Microwave]] — electromagnetic radiation with wavelengths from 1 m to 1 mm ### Part B — Propagation, fading and link budgets - [[Radio_propagation]] — behaviour of travelling radio waves - [[Line-of-sight_propagation]] — characteristic of electromagnetic radiation - [[Skywave]] — propagation of radio waves beyond the radio horizon - [[Ground_wave]] — radio wave propagating along the Earth's surface - [[Ionosphere]] — ionized part of Earth's upper atmosphere - [[Multipath_propagation]] — concept in radio communication *(sim above)* - [[Fading]] — term in wireless communications - [[Rayleigh_fading]] — radio signal statistical model - [[Free-space_path_loss]] — path loss of radio transmitted through air or vacuum *(sim above)* - [[Link_budget]] — accounting of signal gains and losses in communications - [[Friis_transmission_equation]] — formula in telecommunications engineering of antenna performance ### Part C — Antennas and transmission lines - [[Antenna_(radio)]] — device that transmits and receives radio waves *(sim above)* - [[Monopole_antenna]] — class of radio antenna - [[Yagi–Uda_antenna]] — type of radio antenna - [[Radiation_pattern]] — directional variation in strength of radio waves - [[Directivity]] — measure of how much of an antenna's signal is transmitted in one direction - [[Standing_wave_ratio]] — measure used in radio engineering and telecommunications *(sim above)* - [[Reflection_coefficient]] — measure of wave reflectivity - [[Coaxial_cable]] — electrical cable with concentric conductors ### Part D — Receivers and detection - [[Radio_receiver]] — device for receiving radio transmissions - [[Crystal_radio]] — simple radio receiver circuit for AM reception *(sim above)* - [[Direct-conversion_receiver]] — type of radio design - [[Envelope_detector]] — electronic circuit - [[Software-defined_radio]] — radio communication system implemented in software - [[Automatic_gain_control]] — electronic circuit to automatically adjust signal strength ### Part E — Modulation, broadcasting and history - [[Single-sideband_modulation]] — electronic method of transmitting information with a carrier wave *(sim above)* - [[Sideband]] — radio communications concept - [[AM_broadcasting]] — radio broadcasting using amplitude modulation - [[Guglielmo_Marconi]] — Italian electrical engineer and inventor (1874–1937) - [[History_of_radio]] — the build-out from spark telegraphy to broadcast regulation --- *Spine portal, curated (WIKI_RULES §7). Assets: 37 child articles (gate-verified) + 7-sim three.js slate (SHIP, awaiting Netlify deploy). Pack: `specs/portals/PORTAL_Radio.pack.json`. Sibling spines: [[PORTAL_Signal_Processing]], [[PORTAL_Radar]].*