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No pressure altitude in my F1

Robb

Well Known Member
I no longer have a pressure altitude reading on my transponder and Garmin 430. I am not an avionics specialist so I am at a loss. I have dual GRT Horizon displays and may have configured a setting incorrectly when setting up my ADSB. I installed a UAT Echo and it was operating correctly. My question is if the GRT transmits the signal or is it from another dedicated device or signal? I get a message that says no input signal channel 1 on my 430 and no altitude on my transponder.
 
What model transponder? Do you have a stand-alone encoder? One way of sending PA data from the Hx to a transponder (and then from the transponder to the 430) is to set an RS232 out port on the Hx to ‘fuel/air data (Z format)’, baud rate 9600. To know what port you’ll have to trace the wire from the transponder back to the Hx.
 
From the 327, you should have a wire from pin 19 (most likely)(RS232-in #1) or pin 2 (less likely)(RS232-in #2) running to one of the RS232-out pins on one of the Hx units. The Hx port should be configured for ‘fuel/air (Z format)’ and 9600 baud. The 327 port should be configured for ‘FADC w/ALT’ and 9600 baud.
For the 430, one of its RS232-in ports should be configured ‘Shadin FADC’ at 9600 baud. This port can be wired to any of the following: (1) the 327 RS232-out (pin 20); or (2) spliced into the same wire going from the Hx to 327 pin 19; or to another Hx rs232-out port configured for fuel/air data (z format).
Since both the 327 and 430 seem not to be getting data, I’d start by tracing the wire from the 327 pin 19(most likely) to the Hx, and see what pin (and what rs232 port) it’s attached to. Then see if that Hx port is configured as above, ‘fuel/air (Z format)’, 9600 baud.
 
Thanks so much for the information Bob. I will check everything today and see if I can figure it out. I cant stand broken air planes. Ill let you know if I get it going. Really appreciate the help
 
I am a little confused. Is there a dedicated device that broadcast the pressure altitude?
 
Is there a dedicated device that broadcast the pressure altitude?

The GRT screen will put out a signal (serial line) with the altitude. The transponder reads this signal and broadcasts the value.
 
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Your transponder and adsb-out both broadcast pressure altitude. (ATC computers change it to calibrated altitude for controllers). Your Hx sends pressure altitude out in its data stream when formated ‘fuel/air data (z format)’, regardless of its altimeter setting. If you have set a different value in your Kollsman window (‘altimeter setting’) than what ATC is using, they will think you’re at the wrong altitude.
Edit. Just to be clear, you do not need to put 29.92 into the altimeter setting - the grt will calculate pressure altitude for the transponder and adsb. Use 29.92 only when that is in fact the altimeter setting, or at and above FL180, or just briefly if you want to see your PA. BTW, some transponders will display your pressure altitude (usually labeled FL).
 
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Edit. Just to be clear, you do not need to put 29.92 into the altimeter setting - the grt will calculate pressure altitude for the transponder and adsb.


Thanks Bob, will edit my post to reflect this.

Robb, listen to Bob-----he is on top of this stuff.
 
Ill dig into it this weekend. It has to be a setting on my GRT units. It was working fine before my annual. I see that on flight aware I no longer am broadcasting altitude anymore since I had everything apart. ****
 
It has to be a setting on my GRT units. It was working fine before my annual.

Good luck, this is now bordering on voodoo.

Couple ideas----

Baud rate.

Is it possible when you setup the ADSB you re-assigned a serial port?
 
Until you get it fixed, you should probably: turn adsb-out off; run transponder in mode A; avoid mode C required airspace. Or risk a nasty letter from the FAA.
 
I will probably see If I can find a local shop to look at it. If not I am not sure how i will get it to Sacramento. Maybe I can find a guy that can travel and look at it
 
Call norcal on the phone, ask for permission to come in with mode A, no adsb. But first check the grt’s rs232 settings, and have a look behind it for any loose wires.
 
All set for now thanks to Laars help programming the GRT screens. I think its time for an upgrade on the EFIS.The new GRT screens are a lot better than my old displays
 
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