January 14, 2026
Rise time meets roast time
How can I build a simple pulse generator to demonstrate transmission lines
Home-built pulse gizmo lights up the lab as comments clash: retro hacks vs GitHub kits
TLDR: A DIY pulse generator shows how signals bounce in cables, sparking a comments showdown: the classic Jim Williams circuit vs retro tunnel-diode hacks vs a clever “use the cable as a capacitor” trick. It matters because real lab tricks beat theory, and the best tips came from the crowd.
An engineer dropped a DIY “pulse generator” — a little box that makes fast blips to show how signals travel down cables — and the community did what it does best: turn learning into lively drama. The write-up demos reflections (echoes), ringing (wiggles), and why cable length matters, all with cheap TV coax and a 50 MHz scope. It’s geeky, sure, but the author keeps it hands-on and invites alternative builds — basically a lab lesson wrapped in a challenge.
Then the comments ignited. KK7NIL waves the flag for legend status with the “classic” Jim Williams pulse generator, while hilbert42 shows up like the retro boss with a tunnel-diode trick that flips faster than your coffee maker — a throwback flex that screams “we were doing this before GitHub existed.” Meanwhile, efskap praises using Stack Exchange as a blog-style lab notebook, calling it a collaborative vibe, and HNisCIS points to a hidden gem: using a piece of cable like a tiny capacitor to pull off the same stunt. Cue jokes about engineers arguing over 75 ohms like it’s pineapple-on-pizza. SilentM68 sums it up with a meme-worthy “That’s pretty cool.” Verdict: a wholesome nerd brawl with real lab cred, nostalgia, and hacks galore.
Key Points
- •A simple PCB-based pulse generator achieved a measured 3 ns rise time, suitable for transmission line demonstrations.
- •Clear waveforms require matching pulse rise time, oscilloscope bandwidth, and cable length; with a 50 MHz scope, ~50 ft cable is recommended.
- •RF TV coax was used as a cheaper alternative to BNC; termination resistances may need fine-tuning due to ~10% impedance variance.
- •Five impedance configurations were documented, showing reflection, absorption, ringing, and voltage-stepping behaviors.
- •The source-terminated open-load method yields good signal quality only at the line end; branching off additional loads degrades signal integrity.