I am fairly sure this is new. What could cause it?
It was today at FL160, and the altimeter was rock solid.
Watch the video as I could, I saw only the slightest vibration in the VSI needle – indeed it is much more stable than I ever saw mine. But then I do not have an autopilot, and also fly much lower. Also, I learned in ground school and from experience that the VSI is the most sensitive of the barometric instruments. So I see nothing unexpected.
Talking of constant altitudes: watching your flight to Praha on an ADS-B site, I was impressed to see your indicated altitude at a dead constant 12998 feet. Could it be that your ADS-B transmits the autopilot “should” altitude rather than what is actually measured? Or would this have been a little trick of flightradar24?
What could cause it?
It’s nothing, VSI is sensitive instrument and small drraughts in combination with autopilot can cause such readings. Altimeter would be rock solid on even larger fluctuations. If it’s leak in pitot-static system you would notice that on the other instruments.
Talking of constant altitudes: watching your flight to Praha on an ADS-B site, I was impressed to see your indicated altitude at a dead constant 12998 feet. Could it be that your ADS-B transmits the autopilot “should” altitude rather than what is actually measured? Or would this have been a little trick of flightradar24?
That data can come only from my Mode S pressure altitude, which is returned to nearest 100ft AFAIK… possibly 25ft. The autopilot certainly holds it within 25ft. The GTX330 pressure altitude reading is nearly always “exact” e.g. FL160 not 159 or 161. Just very occassionally it will drop down to 159 and then climbs back up – an artefact of the KFC225 firmware.
I don’t have ADS-B. Almost nobody in light GA is radiating ADS-B. All I radiate on Mode S is the pressure altitude and the aircraft speed range band which I think is 150kt. Plus the tail number and the 24-bit ID.
I guess the 12998 is 13000 but somebody is using dodgy 16-but integer maths 
I believe there are “ADS-B” sites that now display the positions and altitudes of non-ADS-B equipped aircraft (Mode S). The position is determined by triangulation from several ground stations.
I guess the 12998 is 13000 but somebody is using dodgy 16-bit integer maths
In the year 2014? Come on, be serious…
Almost nobody in light GA is radiating ADS-B.
I am less sure. There seem to be a fair amount of D-Mxxx with ADS-B now already, and more and more – no lack of budget, as yet, in Teutonia! Seeing the price of a Trigg transponder, and a few more, there is no real surprise. And as soon as I have any budget to spend on the flying side, a Trigg mode-S/ADS-B is my first add-on, too. There’s too many places requiring mode S, and once I go for it, I can as well do it right out, i.e. including the ADS-B.
In the year 2014? Come on, be serious
Transponder data packets use octal. No digit bigger than 7. How old is that? 1950s probably.
Isn’t ADS-B receivers/transmitters rather complex stuff, requiring FPGA to work properly? A colleague of mine is programming these FPGA-stuff in LabVIEW, but I have never really understood what FPGA is, only that it processes data at insane speeds 
Isn’t ADS-B receivers/transmitters rather complex stuff, requiring FPGA to work properly?
Haha… Mode-S was specifically designed to be very simple to implement.
See here, In addition to the probability of error per bit, however, the choice of modulation and mesage format depends on the capacity required, bandwidth occupancy, and cost of implementation. This list consideration is especially important with regard to the transponder.
ADS-B is only some bit coding over the Mode-S physical layer, something that can easily be done with an 8bit micro.
I am less sure. There seem to be a fair amount of D-Mxxx with ADS-B now already, and more and more – no lack of budget, as yet, in Teutonia! Seeing the price of a Trigg transponder, and a few more, there is no real surprise. And as soon as I have any budget to spend on the flying side, a Trigg mode-S/ADS-B is my first add-on, too. There’s too many places requiring mode S, and once I go for it, I can as well do it right out, i.e. including the ADS-B.
Well, it doesn’t make any sense to install A/C only and limit you to airspace below 5000 ft and outside of most controlled airspace (well, not counting E then). So the Transponder would be there anyway. Given, that the microlight fleet is much younger and paperwork costs of installation pretty much doesn’t exist, the percentane of A/C/S-XPDR in the microlight fleet is a bit higher. Then, they just plug in the VFR-GPS into the XPDS and get an unverified ADS-B out. Not sure, if TCAS will ignore, but the base stations of the internet radars don’t. And I think VFR Traffic solutions don’t either.
