Smith Match

Interactive, accessible Smith chart for calculating and explaining lossless single shunt-stub impedance matches—entirely in your browser.

Try Smith Match live

Smith Match places a load on a native SVG Smith chart, rotates it toward the generator to both valid $g=1$ junctions, calculates an open- or short-circuited shunt stub, and presents practical construction lengths with residual verification.

Capabilities

• Impedance, admittance, reflection-coefficient, pointer, touch, and keyboard load entry
• Both canonical matching solutions with electrical, metric, and customary lengths
• Impedance, admittance, or combined chart grids with textual equivalents
• Shareable URL state, standalone SVG export, and printable worksheet
• Responsive light/dark UI, reduced-motion support, and offline reload after a successful visit
• Pure TypeScript RF engine checked against an independent Python formulation

Model limits

Version 1 models one frequency, a real positive characteristic impedance, lossless feed line, and one lossless open or short shunt stub. It is not a VNA, circuit simulator, frequency sweep, lossy-line model, or microstrip synthesizer. Calculated lengths are starting values: connectors, discontinuities, dielectric tolerance, coupling, nearby objects, and line loss affect a physical build.

Quick start

Use Bun 1.3.14, matching CI and the committed lockfile.

git clone https://github.com/wmacomber/smithchart.git
cd smithchart
bun install --frozen-lockfile
bun run dev

Vite prints the local development URL, normally http://localhost:5173/. Bun installs dependencies and runs scripts; deployed code uses no Bun runtime API. bun run build emits static files in dist/.

Use the instrument

1. Enter the load as impedance, admittance, or reflection coefficient—or move the chart marker.
2. Set characteristic impedance, frequency, velocity factor, and open/short termination.
3. Compare Solution A and B, then select the construction that fits the installation.
4. Share the calculation URL, export a standalone chart, or print a worksheet.

Keyboard users can focus Load marker, use Arrow keys for fine movement, Shift+Arrow for coarse movement, Enter to commit, and Escape to cancel. The visible Chart summary supplies a complete text equivalent.

Architecture

URL calculation state ──► reducer/history ──► pure RF solver ──► chart + results
                                ▲                    │
localStorage preferences ───────┘                    └──► sanitized SVG/print output

static Vite build ──► GitHub Pages ──► service-worker application precache

src/rf owns deterministic domain math and imports nothing outside itself. src/chart owns SVG geometry and interaction mapping. src/app owns state transactions. src/features owns workflows; src/persistence owns browser boundaries. No backend, account, analytics, or runtime API exists. The RF modules are internal reusable code, not a published package API. See the full architecture and ADRs.

Mathematics and signs

The solver uses the $e^{+j\omega t}$ phasor convention. Positive reactance is inductive; positive susceptance is capacitive. With distance measured from load toward generator,

$$ \Gamma(d_\lambda)=\Gamma_L e^{-j4\pi d_\lambda}, $$

so movement is clockwise in mathematical reflection-coefficient space. Mathematical positive imaginary values appear above the chart axis; only the renderer inverts SVG Y coordinates. Feed-line and stub lengths use $[0,0.5\lambda)$; the shorter feed-line distance is Solution A.

See mathematics, authoritative sign conventions, and RF reference evidence.

Develop and verify

Command	Purpose	Prerequisite / artifact	In bun run ci
bun run dev	Start Vite development server	Installed dependencies	No
bun run build	Type-check and create production build	Writes dist/	Yes
bun run preview	Serve an existing production build	Run bun run build first	No
bun run format:check	Check Prettier formatting	None	Yes
bun run lint	Run ESLint	None	Yes
bun run typecheck	Run project TypeScript builds	None	Yes
bun run test	Run all Vitest tests	Writes temporary cache only	Yes
bun run test:rf	Run focused RF tests	None	No
bun run test:chart	Run focused chart tests	None	No
bun run test:e2e	Build, preview, and run Playwright matrix	Installed browser binaries	No
bun run test:e2e:pages	Test /smithchart/ offline deployment path	Chromium	No
bun run check:rf-boundary	Prove RF code remains pure and standalone	None	Yes
bun run verify:references	Run dependency-free Python RF verifier	Python 3	Yes
bun run verify:no-runtime-network	Reject runtime network APIs/assets	None	Yes
bun run verify:assets	Enforce JS, CSS, and precache budgets	Current dist/	Yes
bun run verify:offline	Audit service-worker/base-path artifacts	Current dist/	Yes
bun run verify:docs	Verify docs, ADRs, screenshots, versions, notices	Frozen install	Yes
bun run verify:reproducible-build	Compare two clean build digests	Writes dist/ twice	No
bun run licenses	Print verified lock-aligned license inventory	Frozen install	No
bun run licenses:write	Regenerate reviewed license/notice artifacts	Intentional file changes	No
bun run capture:docs	Regenerate curated README screenshots	Chromium; intentional file changes	No
bun run ci	Run deterministic pull-request gate	Bun 1.3.14, Python 3	—

Install Playwright browsers once with bunx playwright install --with-deps. Browser, accessibility, visual, performance, export, and offline suites are documented in testing.

Accessibility, privacy, and security

Mouse, touch, keyboard, textual, reduced-motion, forced-color, reflow, and desktop/mobile browser workflows have automated coverage. Automated ARIA-tree and axe evidence gates releases; manual VoiceOver and TalkBack sessions remain welcome exploratory validation. Details and known limits live in accessibility documentation.

Calculation state appears in the URL and may be visible in browser history or copied links. Display preferences remain in local storage. The app sends neither to a server. A visited build can reload offline after service-worker activation; first-ever offline loading and installable PWA behavior are not supported. Report vulnerabilities privately under the security policy.

Contributing and license

Read Contributing, the Code of Conduct, and Security Policy before opening work. Changes follow the changelog and versioning policy.

Smith Match is MIT licensed; project files need no additional per-source license header. Distributed dependency notices appear in Third-Party Licenses. External RF sources establish method and convention; project fixtures remain project-authored evidence and imply no endorsement.

Origin

Smith Match was inspired by Veritasium's The Scariest Chart In Electrical Engineering. The chart turned a half-learned antenna lesson—why an apparently disconnected wire can improve a received signal—into transmission-line behavior that could be seen, calculated, and built.