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  #1  
Old 03-25-2021, 08:22 PM
Robb Robb is offline
 
Join Date: Sep 2015
Location: Nevada City Ca
Posts: 231
Default No pressure altitude in my F1

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.
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  #2  
Old 03-25-2021, 09:38 PM
BobTurner BobTurner is offline
 
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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.
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  #3  
Old 03-25-2021, 10:35 PM
Robb Robb is offline
 
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My transponder is a Garmin 327.
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  #4  
Old 03-26-2021, 12:17 AM
BobTurner BobTurner is offline
 
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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.
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  #5  
Old 03-26-2021, 07:31 AM
Robb Robb is offline
 
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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
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  #6  
Old 03-26-2021, 05:32 PM
Robb Robb is offline
 
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I am a little confused. Is there a dedicated device that broadcast the pressure altitude?
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  #7  
Old 03-26-2021, 05:44 PM
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Mike S Mike S is offline
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Quote:
Originally Posted by Robb View Post
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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Last edited by Mike S : 03-26-2021 at 06:34 PM.
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  #8  
Old 03-26-2021, 05:52 PM
BobTurner BobTurner is offline
 
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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).

Last edited by BobTurner : 03-26-2021 at 05:59 PM.
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  #9  
Old 03-26-2021, 06:33 PM
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Mike S Mike S is offline
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Quote:
Originally Posted by BobTurner View Post
Y
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.
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VAF 909

Rv-10, N210LM.

Flying as of 12/4/2010

Phase 1 done, 2/4/2011

Sold after 240+ wonderful hours of flight.

"Flying the airplane is more important than radioing your plight to a person on the ground incapable of understanding or doing anything about it."
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  #10  
Old 03-26-2021, 06:47 PM
Robb Robb is offline
 
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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. ****
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