#measurement.
Posts on the Alpisto engineering blog filed under #measurement.
- 01#flybeeper #fanet #ads-l
One radio, two networks: how a FANET vario shares every second with ADS-L
My vario has one radio and two networks to serve. Every second it decides which one to listen to and when to speak, and that choice decides who you see on the map. The numbers from the bench: listen to ADS-L for the whole second and FANET goes to zero; stop listening to ADS-L and FANET comes back 40 to 140 % stronger; cut the ADS-L window from 550 to 300 ms and another maker's transmitter drops from 61 % of its seconds heard to 34 %.
12 min read - 02#flybeeper #fanet-vario #fanet
The lift does not fade: where 11,046 competition thermals end, and how to know before you get there
The usual advice is to leave a thermal when it weakens. In 11,046 thermals from competition tracks it hardly weakens at all: pilots climb at full rate to within a hundred metres of the top, and the last fifty metres still give most of it. The top is a ceiling, and your own vario cannot see a ceiling coming. The pilots around you can: the ones who have already left, and the tops of the day's earlier thermals, tell you how much is left to within about a hundred metres, a minute before you get there.
9 min read - 03#flybeeper #fanet-vario #fanet
The thermal leans, then it drifts: 8,409 thermals rebuilt from competition tracks
Every pilot knows a thermal drifts with the wind. How much, and in what way, a single pilot cannot tell: climbing and drifting happen at the same time. A competition gaggle can — a hundred pilots in one thermal at different heights in the same minute. From the published tracks of 28 competitions on 18 sites I rebuilt the axis of 8,409 thermals. In the mountains, near the ground, the column stays put and the wind lays it over at 45°; over flat land, and higher up everywhere, it stands nearly straight and the whole thing drifts at two thirds to three quarters of the wind. And the radio a FANET vario already listens to is enough to see it from the air.
21 min read - 04#flybeeper #fanet-vario #sun-vario
The note that never sounds: what a piezo vario actually plays
Small varios beep in a way nobody would call pleasant, and it is not because nobody cared. A piezo disc is a bell with one note of its own, and a vario plays a tune on it by feeding it square waves and letting the bell pick what it likes. I put one in a desk drawer with a microphone: at 1000 Hz the note that was asked for comes out 33 dB below its own third harmonic, loudness swings 16 dB across the tone table, and the obvious way to soften a beep turns out to make it sharper.
17 min read - 05#flybeeper #sun-vario #variometer
Fourteen metres that were never there: a soldered barometer's thermal drift
Everyone who builds these devices knows you must not solder near the barometer, and that the third rework kills it. Nobody says by how much. This one came off the bench at 470 Pa/K against a rated 0.5, inventing 14.5 metres of climb while sitting still. Thirty lines of firmware removed 95 % of that and every bench test agreed — until somebody picked the device up and the vario went the wrong way. The number behind the folklore, and why the fix helps an altimeter and provably cannot help a variometer.
24 min read - 06#flybeeper #sun-vario #variometer
Measuring a vario with a USB tester: 20 seconds per mode, and 420 µA that were never mine
I spent eight hours per data point measuring a solar variometer through its own capacitor. Then I measured the same device directly with a USB tester and got a full consumption curve in twelve minutes — along with a 420 µA floor that belonged to the cable, not the device. What both methods agree on, where they don't, and how to read a WITRN tester from Linux.
14 min read