w5isp.com/IDEAS.md

Future interactive post ideas

Working scratch list. Same format as the NLOS post: vanilla JS, 2D canvas, scenes scoped to a single post via <link> and <script> tags in the markdown. Each idea is a candidate; most of these are one-post-sized if focused.

Electronics

• How a transistor actually amplifies. Draggable base current / gate voltage on a NMOS or NPN schematic, live I-V curve on the side, carrier flow animation in the channel or base region. Payoff: "small signal gain" stops being a formula and becomes something you can see. Written 2026-04-23: how-a-transistor-amplifies.
• LC resonance from scratch. Tank circuit with sliders for L, C, and drive frequency. Show the phasors rotating, impedance magnitude/phase sweeping, and a scope trace of voltage vs current. Payoff scene: pumping the tank at resonance and watching it ring.
• An oscillator starting up. Colpitts or similar. Start from noise, show the limit cycle forming, let the reader nudge the loop gain and see it either die off or run away.
• Feedback loop stability. Drag the poles and zeros around on the s-plane, watch the step response and the bode plot change. The moment a pole crosses into the right half plane and everything goes sideways.
• A superhet receiver, piece by piece. Antenna, RF amp, mixer, LO, IF filter, detector. Tunable signals scrolling through the spectrum, user drags the LO, watches the desired signal slide into the IF passband. Image rejection as a visible thing.
• A switching power supply. Buck converter with a slider for duty cycle. Inductor current ramping and freewheeling, output ripple. Makes the "magic efficiency" of SMPS feel earned.
• Noise figure, cascaded. Build a receiver chain by dragging in blocks (LNA, mixer, IF amp), each with a noise figure. Live link budget at the bottom. The Friis formula stops feeling abstract. Written 2026-04-29 (scheduled): cascaded-noise-figure.
• Op-amp, opened up. Differential pair on the left, gain stage in the middle, push-pull output on the right. Slider for input differential voltage, watch the tail current redistribute and the output swing. Then close the loop with a feedback resistor and watch virtual ground appear out of nothing.
• Schmitt trigger hysteresis. Noisy input riding on a slow ramp. Slider for the hysteresis band. Without it the output chatters wildly at the threshold; widen the band and the chatter stops. Show the two trip points moving on the transfer curve.
• A SAR ADC, bit by bit. Sample-and-hold capacitor charges, then the comparator and DAC binary-search the input. Step through each bit, watch the trial voltage close in on the sample. User can change resolution and see conversion time scale.
• PLL locking. Reference oscillator on one side, VCO on the other, phase detector and loop filter in between. Slider for loop bandwidth. Watch the VCO drag itself into lock, then perturb the reference and see the loop track. Crank the bandwidth too high and watch it ring.
• Linear regulator vs LDO. Pass transistor, error amp, reference. Slider for input voltage and load current. Drop the input toward the output and watch a standard regulator fall out of regulation while the LDO holds on. Power dissipation rendered as a thermometer on the pass element.
• Crystal oscillator startup. Pierce topology with the crystal modeled as its motional RLC plus shunt capacitance. Start from thermal noise. Slider for negative resistance from the active stage. Too little and it never starts; just enough and you watch a clean sine build over thousands of cycles.
• Class-D from triangle and comparator. Audio in, triangle carrier, comparator output as a PWM stream, LC filter recovering audio. Slider for switching frequency and modulation depth. The moment the recovered waveform looks identical to the input despite the output stage being only ever fully on or fully off is the payoff.
• Charge pump, bucket by bucket. Two capacitors and four switches. Step through the phases by hand at first, then let it run. Output voltage climbs to roughly twice the input. Add load current and watch the output sag, then crank the switching frequency to recover it.

Computers / networking

• A TCP connection, from the packets' perspective. Client on the left, server on the right, sequence numbers and window sizes visible, user can introduce loss or latency and watch congestion control react. Slow start, fast recovery, the window collapsing on a single dropped packet. Written 2026-04-27 (scheduled): how-tcp-and-udp-work. Also covers UDP.
• How DNS actually resolves a name. Recursive resolver, root, TLD, authoritative, caching. User types a hostname, watches the queries fan out with their TTLs.
• What a CPU does per cycle. A tiny toy ISA executing step by step. Pipeline stages, hazards, stalls. Adds a register renamer in a second scene and you get a decent intuition for why modern CPUs are fast.
• Cache coherence (MESI). Two cores, a shared line of memory, user issues reads and writes, arrows show the invalidations flying around. The reason your "obviously correct" lock-free code isn't is usually on this graph somewhere.
• BGP finds a route. A handful of ASes with peering relationships, user picks source and destination, watches announcements propagate and the path emerge. Bonus scene: a single misconfigured announcement leaking and causing a global outage.
• Virtual memory and page tables. Process issues a virtual address, the MMU walks the levels, TLB hits and misses, page fault handling. Good payoff if tied to a real program's memory map.
• Diffie-Hellman in colored paint. Two parties, a public modulus, private exponents kept hidden. Watch the shared secret emerge while an eavesdropper sees only the public exchange. Slider for prime size to show why small primes are trivially broken and large ones are not.
• Huffman coding live. Type a string, watch the frequency table build, then the tree assemble bottom-up, then the bit codes fall out. A second pane shows the encoded length shrinking as the message gets more redundant.
• NAT and a stuck connection. Two clients behind NATs trying to reach each other. Show the translation tables, the dropped SYNs, then a STUN server learning the mapped ports, then a hole punch succeeding. The reason video calls feel like dark magic becomes a diagram.
• ARP, the unsung protocol. A host wants to send a packet, has an IP, needs a MAC. Broadcast goes out, reply comes back, cache populates with a TTL. Second scene: a gratuitous ARP from a duplicate IP and the resulting chaos.
• Raft electing a leader. Five nodes on a ring, term counters, randomized election timeouts. User can pause a node, partition the network, watch a new leader emerge and then watch the old one rejoin and step down. The split-brain scenario as a movable thing.
• Token bucket rate limiting. Bucket fills at a steady rate, requests drain it. Slider for fill rate and burst size. Send a burst of requests and watch which get through and which get 429'd. Compare side-by-side with a leaky bucket.
• Garbage collection, three flavors. Same heap, same allocation pattern, three collectors running in parallel panes: mark-sweep, copying, generational. Watch pause times and fragmentation diverge. Slider for allocation rate to find where each collector falls over.
• Branch prediction history. A loop with a data-dependent branch. Toggle between always-taken, two-bit saturating counter, and a small perceptron predictor. Mispredict rate and pipeline bubbles rendered as wasted clock ticks.
• A load balancer at work. Incoming requests, a pool of backends with varying response times. Switch between round robin, least connections, and consistent hashing. Kill a backend and watch the failure modes differ.
• Subnetting IPv4. An address and a prefix length. Slider from /8 to /30. Bits light up in the network and host portions. Host count, usable range, broadcast address, and subnet mask all recompute live. Second scene: take a /22 and carve it into a /24 + /25 + /26 + /27 + /28 to fit a specific set of site sizes. Overlap and waste rendered visually so VLSM clicks. Third scene: two hosts with given addresses and masks; show whether they're on the same subnet and, if not, what the gateway decision looks like.
• Layer 2 and layer 3, side by side. A small network: a few hosts, a switch, a router, two subnets. A packet leaves a host with a destination IP on the other subnet. Watch the ARP for the default gateway, the L2 frame addressed to the router's MAC, the router rewriting the L2 header and forwarding out a different interface, another ARP on the far side, final delivery. Toggle between a hub (collisions visible), a learning switch (MAC table filling in), and a router (routing table consulted per packet). Second scene introduces VLANs and trunking: the same switch logically split, a trunk port carrying tagged frames, the router-on-a-stick doing inter-VLAN routing. The phrase "broadcast domain" stops being abstract.
• TCP in the weeds (follow-up to how-tcp-and-udp-work). MSS negotiation, Path MTU Discovery, segmentation of a 10 KB write into 1460-byte segments, fast retransmit and SACK, delayed/accumulated ACKs, Nagle's algorithm, the PSH and URG flags, connection teardown with FIN/FIN-ACK and the TIME-WAIT state, keepalives and persist timers. One scene per mechanism with a small packet diagram each. Written for the reader who already understands the basics.

Ham radio

• SSB, from audio to RF. Mic input on the left, phasing or filter method in the middle, RF out on the right. Show the audio spectrum, then the DSB-SC product, then USB after filtering or phasing. Bonus: demodulate it back on the receive side with a BFO offset and watch Donald Duck.
• FT8 end to end. 77 bits of payload, LDPC encoding, Costas sync, GFSK shaping, Gaussian noise, decoder pulling it back out under the noise floor. The part where you add enough AWGN to make the signal invisible and the decoder still pulls it is the Adams moment.
• An SDR front end. Antenna, bandpass, mixer with quadrature LO, anti-alias, ADC, decimation filters. User chooses the tuning frequency and the SDR slides through the spectrum.
• Great circle and grid square math. Enter two grid squares, get the path, bearing, distance. Drag either endpoint on a globe. Small but useful.
• HF skip vs MUF. Ionospheric layers with time-of-day and solar-cycle sliders. Rays launching at various angles, reflecting (or punching through) D/E/F layers, landing somewhere else on the globe. Great contrast piece to the NLOS post.
• Feedline loss as a function of length, frequency, and type. Slider for length, buttons for RG-58/RG-8/LMR-400/heliax. A visible chunk of transmit power disappearing into the coax as frequency climbs.
• CW keying waveforms and key clicks. A keyed carrier with adjustable rise and fall times. Time domain on the left, spectrum on the right. Hard keying produces audible-looking sidebands sprawling across the band; smooth shaping pulls them in. Slider for WPM to show the trade against keying speed.
• QSK, in slow motion. Transmit relay, PA, T/R switching, receiver muting, all on a millisecond timeline. User adjusts the keying speed and watches the sequencer's headroom shrink. The point at which the receiver hears its own backwave becomes obvious.
• APRS packet over the air. A position report becoming an AX.25 frame, then AFSK tones, then audio out. Inject noise on the channel and watch a digipeater either decode and forward or drop the frame. Second scene shows the path field accumulating hops.
• Yagi pattern, element by element. Start with a driven dipole. Add a reflector behind it, watch the back lobe collapse. Add directors out front one at a time, watch the main lobe sharpen and the side lobes appear. Slider for boom length sweeps gain against beamwidth.
• Antenna tuner matching anything. L-network with two variable components. User picks an arbitrary load on a Smith chart, watches the tuner walk the impedance toward 50 ohms. Show the loss in the tuner climbing as the mismatch gets ugly.
• Baluns, currents, and common mode. A coax-fed dipole with no balun, current on the shield rendered as a moving arrow. Add a choke balun, watch the common-mode current die. Receiver noise floor in a side panel drops as the feedline stops radiating.
• Lightning and station grounding. A strike hits the tower. Trace the current down through the ground rods, across the bond to the shack ground, and (without a single-point ground) up through the radio and out the AC mains. Toggle a proper ground window and watch the current bypass the gear.
• QRP propagation reality check. Slider for power from 100 W down to 100 mW. Path loss, noise floor, and required SNR for SSB, CW, and FT8 plotted as bars. The point where 5 W on FT8 still closes the link but 100 W on SSB does not is the punchline.

Microwave / advanced RF

• Rain scatter. A rain cell, two stations not in LOS, common volume in the cell. Slider for rain rate, frequency. Show how a signal bounces off the precipitation and arrives from a totally wrong direction. Natural follow-up to the NLOS post.
• Meteor scatter. A meteor streaking through the ionosphere leaving a plasma trail, signal reflecting during the brief window. Ping lengths, burst rates. An argument for why 6 meters is worth owning a rig for.
• EME (moonbounce). Lunar geometry, path length, Doppler spread from libration, degree of polarization rotation from Faraday. Answer to "why do I need a big dish for this" becomes visually obvious.
• Phased array beam steering. Array of elements, user slides the phase taper, the beam sweeps. Grating lobes appear if spacing is too wide. Explains why Starlink and every modern radar system looks the way it does.
• Smith chart, but friendly. Drag a load impedance, watch reflection coefficient, SWR, and return loss update. Add a matching network with an L-network or stub and watch it slide to the center.
• Parabolic dish aperture. Slider for diameter and frequency, see gain vs beamwidth vs sidelobes. Illumination taper as a second control, showing the efficiency / sidelobe trade.
• ITU-R P.838 rain attenuation. Pick a frequency, a rain rate, and a path length. Curve of attenuation over the full microwave band. Useful companion to anything on 10 GHz and up.
• S-parameters, demystified. A two-port network with adjustable internal components. Drag a frequency cursor across the band, watch S11, S21, S12, S22 trace out on a Smith chart and a magnitude plot in lockstep. Toggle between an amplifier, a filter, and an attenuator and see what each one's signature looks like.
• Stub matching on a transmission line. A mismatched load at the end of a line. User slides a shorted shunt stub along the line and adjusts its length. SWR upstream of the stub plotted live. Watch the match snap into place at the right position.
• Prime focus vs Cassegrain. Same dish diameter, two feed geometries side by side. Ray trace the illumination, show the spillover and the blockage from each. Slider for f/D and subreflector size to see how the trades shift.
• Polarization tracking a LEO bird. A satellite with linear polarization passing overhead. Show the apparent polarization angle rotating from horizon to horizon as geometry changes. User dials a manual rotator to keep up, or enables auto-tracking. Signal strength dips on every degree of mismatch.
• LNA bias network. A GaAs FET with a gate bias tee, drain choke, and decoupling. Slider for drain voltage and gate voltage. Live IV curve, noise figure circles, and gain compression all updating. A second scene adds a missing bypass cap and shows the LNA breaking into oscillation.
• Waveguide modes. A rectangular guide cross-section. User picks a frequency. Below cutoff, nothing propagates; cross the TE10 cutoff and the field pattern lights up. Push higher and TE20, TE01, and TM11 appear with their distinct patterns. Group velocity slowing near cutoff is visible.
• Sun noise as an antenna check. Point a dish at cold sky, then drag it onto the sun. Y-factor in dB updates live. Slider for dish size and frequency derives system noise temperature from the result. Calibration without a noise source.
• Noise temperature and noise figure, two views of one thing. A receiver chain with a slider that toggles the unit between K and dB. Friis recomputes in both. Toss in a lossy feedline ahead of the LNA and watch the system noise temperature jump in a way the noise figure number understates.

Longer arcs

A couple of ideas that would be a whole series, not one post.

• "Build a receiver from first principles." Start at an antenna picking up an EM wave, end at a speaker playing audio. Every stage a scene. Takes the shape of a short book.
• "What the atmosphere is doing right now." Live data from prop.w5isp.com, rendered as an interactive cross-section of North Texas atmosphere at the current hour. Refractivity aloft, ducts forming and collapsing, paths scored against real conditions. Operational rather than explanatory.
• "Every component in my station, demystified." One post per piece of gear. Transverter, PA, sequencer, rotator, preamp. Each one a scene that makes the internal thing you pay for make sense.
• "How GPS knows where you are." A series. One post on pseudoranges and trilateration with four satellites, one on the navigation message and clock corrections, one on ionospheric and tropospheric delay, one on RTK and carrier phase. Each scene builds the previous post's output into its inputs.
• "A radar, from pulse to picture." Start with a single pulse and a target return. Add pulse compression with a chirp and matched filter. Add Doppler processing across a pulse train. Add MTI to suppress clutter. End at a synthetic aperture image of a patch of ground. Each step a scene, each scene reusing the prior one's signal.
• "Light down a fiber." A series on optical comms. Modes in a step-index fiber, then graded index, then single mode. Chromatic and polarization-mode dispersion as time-domain pulse smearing. EDFA gain. Coherent detection and DSP equalization. The series ends with a 400G link budget that actually closes.
• "Control loops that don't ring." PID tuning as a sandbox. A plant (motor, thermal mass, antenna rotator) with adjustable P, I, D. Step responses, disturbance rejection, integrator windup. Second post on cascaded loops. Third on feedforward. By the end the reader has tuned a real-feeling system without wanting to throw the rotator off the tower.

House style

Keep each post focused, one topic, deep. No survey posts. Interactive bits earn the page weight, static bits carry the prose load. No em-dashes. Adams when it fits, silence when it doesn't.