Mode C readout?

[bmarvel]

I know that the D-100 outputs mode C pressure altitude via an RS 232 port and that some transponders will display this altitude to the pilot.

Does the D-100 itself have any way to display this altitude?  I have not seen any.

Bill Marvel
One Dynon system flying in an RV-8A
Installing another in a Zenith 801  

 

[Brantel]

Yep...Sure does...Just turn the altimeter setting to 29.92 and it will show your pressure altitute.

 

[bmarvel]

Sure, that's pressure altitude but not the answer to my question.  I wanted to know if the number that the D-100 is sending to the transponder is available to be seen.  Some transponders can display this but ours cannot.  I was wondering if the D-100 can.      

Bill Marvel

 

[Brantel]

The answer to your question is in my reply.....

The Dynon sends the transponder pressure altitude. So if you set your alt setting to 29.92, the reading you see on your alt indicator is what is being sent to the transponder.....

When you adjust your alt setting to something other than 29.92, the Dynon does not care ... It still sends the pressure alt to the transponder. The alt setting has no effect on what is sent, only on what is displayed.

 

[bmarvel]

Yes, I understand that.  But in all the years I have been flying I have twice been told by center to stop altitude squawk because the Mode C altitude differs from my reported altitude by more than 300 feet.  In one case the problem was with a blind encoder and in the other it was with the encoder portion of an encoding altimeter.  The data sent to the ground via Mode C can be incorrect and that is why I asked the question if this data can be made visible on the D-100 screen.  

Bill Marvel

 

[dynonsupport]

The number when you set the baro to 29.92 IS the number we send out. The software sends this right to the serial port with no modification. Given the way software works, there is no other way for us to give this number to you in an independent way, and we've never seen it be any different. What is displayed on the screen is what is sent out. In a sense, we are ALWAYS displaying what we send out (just tweaking it for the baro adjust right before we display it). We are taking the altitude data we get and sending it out the serial port and displaying it on the screen.

The only way to get a totally independent measure would be to hook up a laptop or other serial device to the output port.

Remember that we are not a mechanical device, and there isn't really a way for it to break on you like it has in the past. The D100 is always displaying the same number it outputs. It isn't a different encoder like a standalone encoder is, and it isn't a series of mechanical contacts unrelated to the needle like an encoding altimeter.

 

[Brantel]

I am trying to tell you twice and Dynon once that what is displayed on the Dynon when you put 29.92 in the alt setting is what is being sent to your transponder.....

If ATC ever does this again, quickly put in 29.92 while at your assigned alt and the Dynon will show you what is being reported via the transponder.   Keep in mind that this may not agree with your
assigned alt since it is not corrected for baro.  The ATC computers correct the reading sent by your transponder for baro automatically so what your ATC guy sees is a corrected alt.

I have no idea how to make this more clear but that is how it works and it works well!!!

Have a great day!

 

[bmarvel]

Dynon tech support explained it quite well by indicating that with this system there cannot be any difference between the altitude shown on the display and the altitude transmitted.  That is what I needed to know.  

With other systems there can be a difference and that is why they have an independent means to show the altitude sent to the transponder.  One missing bit and the difference can be hundreds or thousands of feet as I have encountered in the past.  

Bill Marvel        

 

[jakej]

Bill

That was one of the benefits of the Apollo SL70 transponder, but they don't make them anymore after the Garmin buyout :'( I hope mine lasts a long time.

Jake J

 

[Brantel]

Most of the new ones do this as well.

Bill

That was one of the benefits of the Apollo SL70 transponder, but they don't make them anymore after the Garmin buyout   :'(  I hope mine lasts a long time.

Jake J

 

[Brantel]

Glad you got a second or was it third opinion that this is how it works...

Unless your using the serial to grey code converter, there is no bits to miss.  I suspect that since you have a transponder that does not show the pressure alt that you might be using the converter. (what transponder you using?)

If you are using the converter, the converter could go bad (never heard of this) and start missing bits or you could have a wiring issue or bad connection between the converter and the transponder as a failure mode.  If your using this converter, it is not 100% guaranteed since you have another device and way more wires and connections between the EFIS(the encoder) and the transponder.

With straight serial, it either works or it doesn't.  There is no in between.  

Not sure what other systems you are refering too but I have never seen any Experimental EFIS systems that have a separate display for their encoder output (pressure altitude).  Blind encoders don't have em and neither do encoding altimeters?????

In the old days when everyone used grey code and transponders did not display pressure altitude, the only way to know what was up was to have a transponder check done with one of them fancy test sets.

Dynon tech support explained it quite well by indicating that with this system there cannot be any difference between the altitude shown on the display and the altitude transmitted.  That is what I needed to know.  

With other systems there can be a difference and that is why they have an independent means to show the altitude sent to the transponder.  One missing bit and the difference can be hundreds or thousands of feet as I have encountered in the past.  

Bill Marvel