#measurement.
Posts on the Alpisto engineering blog filed under#measurement.
- 01#flybeeper#fanet#ads-l
One radio, two networks: how my FANET vario splits each second with ADS-L
My vario has one radio and two networks to serve. Every second it has to decide which network to listen to and when to transmit, and that decision affects who you see on the map. Bench results: if the vario listens to ADS-L for the whole second, FANET reception drops to zero; if it stops listening to ADS-L, it receives 40 to 140 % more FANET frames; if the ADS-L listening window is cut from 550 to 300 ms, the share of seconds in which another maker's transmitter is heard falls from 61 % to 34 %.
13 min read - 02#flybeeper#fanet-vario#fanet
The lift does not fade: where 11,046 competition thermals end and how to see it coming
In 11,046 competition thermals the lift hardly fades: pilots climb at full rate almost to the top, so your own vario cannot warn you. The pilots who left before you and the day's earlier tops can, about a minute ahead.
11 min read - 03#flybeeper#fanet-vario#fanet
The thermal leans, then it drifts: 8,409 thermals rebuilt from competition tracks
From the tracks of 28 competitions I rebuilt 8,409 thermals. Near mountain terrain the column stays put and leans at 45°; higher up and over flat land it stands nearly straight and drifts at two thirds to three quarters of the wind.
22 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