Marauder Posted August 20, 2014 Report Posted August 20, 2014 I just went through a rather ugly experience with my plane trying to determine why my altitude was reporting high. Since I have a dual Aspen setup, a standby altimeter and a separate encoder, I get the pleasure of paying for multiple units during the IFR cert. I read on one of these forums that the Aspens are capable of providing altitude encoding information to my Mode C transponder. My encoder is at least 30 years old and if it fails I am looking at the replacement strategy. Does anyone know if the Aspen in fact can provide altitude information to a Mode C transponder? Also, does this mean both Aspens need to be hooked up to provide backup? Quote
KSMooniac Posted August 20, 2014 Report Posted August 20, 2014 I haven't gone through an Aspen installation manual yet, but I suspect they are quite capable of outputting the gray code format that is used by the transponder. If I were you, I would've gotten that hooked up during your installation and removed the old encoder...but perhaps you didn't realize there was that capability when you had yours installed. It should be a pretty simple connection if I had to guess. On my plane, there was a terminal block (added at some point after the plane left Kerrville) that allows any device to "plug in" to the gray code output by the encoder. The GNS boxes and transponder use it, and I later added a connection to my Davtron M655 OAT instrument so it can display density altitude. Pretty easy. 1 Quote
carusoam Posted August 20, 2014 Report Posted August 20, 2014 More benefits of MS. The kind you don't get anywhere else for any price! Thank you gents! -a- 2 Quote
Awful_Charlie Posted August 20, 2014 Report Posted August 20, 2014 The Aspen can do a serial altitude output, but not the grey code. Unfortunately with a 30 year old transponder, it is unlikely to take a serial input, but if you are replacing it with something more modern then you should be ok. As to backup/switchover, unless the transponder can take two inputs and switch itself, I suspect you will end up with a toggle switch to select which provides the feed, but AFAIK you don't actually *need* to have two feeds 2 Quote
KSMooniac Posted August 20, 2014 Report Posted August 20, 2014 Thanks for that info, Charlie. Sounds like one upgrade begets another. The upcoming option for Maruader might be replace the relatively cheap encoder with another one, or buy a modern transponder that can connect to the Aspen via serial connection. Tough call if you plan to replace the transponder "at some point" for ADS-B compliance... Quote
Alan Fox Posted August 21, 2014 Report Posted August 21, 2014 The only encoder that needs to be checked is the one that provides the mode C to the txp... Quote
Marauder Posted August 21, 2014 Author Report Posted August 21, 2014 Thanks guys. The encoder is 30 years old but the transponder was installed in 1993 and is a Narco AT150. Can one of you explain the gray code? And more importantly, will the AT150 be able to handle a serial input. I would love to drop the old encoder if it is not needed. Both of my Aspens are capable of running as PFDs. I have my autopilot setup to allow control to be switched from the primary PFD to the MFD converted to a PFD during reversion. Since they have completely separate AHRS and can act independent of each other, it might make sense to have the switch installed (if needed) and allow for a backup scenario in case the primary PFD fails. Here is the AP throw over switch: Quote
Marauder Posted August 21, 2014 Author Report Posted August 21, 2014 The only encoder that needs to be checked is the one that provides the mode C to the txp... That was part of the problem I was having. I went to the avionics shop to verify the reported output from the encoder to the transponder and was told that although the encoder was off, so were the three altimeters. Sometimes more is not better. Right now, everything is dead nuts on with each other, but I'm trying to figure out if the better solution would be to use the Aspen output to my transponder instead of the blind encoder. With the Aspen providing the data, I would at least be able to see what altitude it is reporting to me and likely the same to the transponder. Quote
Jerry 5TJ Posted August 21, 2014 Report Posted August 21, 2014 Thanks guys. The encoder is 30 years old but the transponder was installed in 1993 and is a Narco AT150. Can one of you explain the gray code? And more importantly, will the AT150 be able to handle a serial input. I would love to drop the old encoder if it is not needed. No, your AT150 won't accept serial altitude input data from an encoder; it accepts a parallel connection only. The "gray code" refers to how the parallel altitude data is coded so that it shifts no more than one line at a time. This helps prevent large jumps in transmitted mode C as the altitude encoder climbs or descends. Quote
Marauder Posted August 21, 2014 Author Report Posted August 21, 2014 No, your AT150 won't accept serial altitude input data from an encoder; it accepts a parallel connection only. The "gray code" refers to how the parallel altitude data is coded so that it shifts no more than one line at a time. This helps prevent large jumps in transmitted mode C as the altitude encoder climbs or descends. Jerry -- thanks for the explanation and the bad news Your explanation also tells me why the avionics shop never mentioned the Aspens being able to drive the encoding piece. They figured they had me with an empty wallet already, so why mention a need to get a new transponder so I can eliminate a 30 year old encoder. Quote
Bob_Belville Posted August 21, 2014 Report Posted August 21, 2014 Chris, when I did my panel, I bought a Garmin GTX 327 for $1795 and sold the working KT76A for $500. Basically solving the same problem you have. (I think I threw in the old blind encoder to the Mooney guy who bought the xponder.) My Aspen provides altitude to the digital xponder. I got by with a cheaper xponder since I also got a GDX 88 for ADS-B i/o. 1 Quote
Alan Fox Posted August 21, 2014 Report Posted August 21, 2014 Chris , I am upgrading to a KT74 and am selling my GTX327 , I also may have an additional GTX327 coming in , I can sell you a 327 for 1200 including tray , and you can have a modern panel very inexpensive , Let me know... 1 Quote
orionflt Posted August 21, 2014 Report Posted August 21, 2014 do I see another copper wire being formed? Quote
Bob - S50 Posted August 21, 2014 Report Posted August 21, 2014 Another option if you just like spending money.... Not sure if we can install the Trig TT22, but if we can, it is a small, light weight, ADS-B capable transponder with a built in altitude encoder. Something to consider anyway. Bob 1 Quote
Marauder Posted August 21, 2014 Author Report Posted August 21, 2014 Chris , I am upgrading to a KT74 and am selling my GTX327 , I also may have an additional GTX327 coming in , I can sell you a 327 for 1200 including tray , and you can have a modern panel very inexpensive , Let me know... You up to some horse trading? I think I got some stuff you may be interested in? Quote
Marauder Posted August 21, 2014 Author Report Posted August 21, 2014 do I see another copper wire being formed? Speaking of copper wire. I asked my avionics shop for all the old wiring they removed. Just kidding, I'm a Cheap Bast$&d, but not that cheap! Quote
Marauder Posted August 21, 2014 Author Report Posted August 21, 2014 Another option if you just like spending money.... Not sure if we can install the Trig TT22, but if we can, it is a small, light weight, ADS-B capable transponder with a built in altitude encoder. Something to consider anyway. Bob Good suggestion. Not sure if the Trig is mode S. If it is I'm hoping to stay away from them. I don't fly flight levels and I certainly don't want my N number transmitting. Quote
Bob - S50 Posted August 22, 2014 Report Posted August 22, 2014 Good suggestion. Not sure if the Trig is mode S. If it is I'm hoping to stay away from them. I don't fly flight levels and I certainly don't want my N number transmitting. It is a Mode S and 1090 ADS-B capable transponder. http://trig-avionics.com/tt22.html Lots of tough choices. Good luck. Bob Quote
Marauder Posted August 22, 2014 Author Report Posted August 22, 2014 It is a Mode S and 1090 ADS-B capable transponder. http://trig-avionics.com/tt22.html Lots of tough choices. Good luck. Bob Yep, sure are. And they want to know why we are all sitting around waiting to make a decision. Quote
Bob - S50 Posted August 22, 2014 Report Posted August 22, 2014 Yep, sure are. And they want to know why we are all sitting around waiting to make a decision. Our group is treating it sort of like a car.... Never buy the first year of a new model. Let others work out the bugs then buy. Or like most other electronics.... The prices always seem to go down while the capabilities increase. Besides we are cheap ..er, I meant thrifty, Mooney pilots !! Let us know what you end up doing. Bob Quote
Awful_Charlie Posted August 22, 2014 Report Posted August 22, 2014 Speaking of copper wire. I asked my avionics shop for all the old wiring they removed. Just kidding, I'm a Cheap Bast$&d, but not that cheap! How do you make copper wire? Give two Mooney pilots a penny 1 Quote
Marauder Posted August 22, 2014 Author Report Posted August 22, 2014 How do you make copper wire? Give two Mooney pilots a penny How do you know they were Mooney pilots? Answer: You had to give them the penny. 2 Quote
Alan Fox Posted August 22, 2014 Report Posted August 22, 2014 Just went to Charlies profile to watch the Juggs Jiggle.. Quote
carusoam Posted August 24, 2014 Report Posted August 24, 2014 Alan's avatar needs to visit Awful Chuck's avatar to get updated... Best regards, -a- Quote
Alan Fox Posted August 25, 2014 Report Posted August 25, 2014 Yes it happened yesterday....Brian and I argued over a few pennies , and I now have a bunch of copper wire.......I cant explain it but somehow Brian got a free set of flap gap seals,,,, Quote
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