New encoder required for 340 install?
Printed From: Avidyne
Category: Avidyne General
Forum Name: AXP340/322 ADS-B Transponder
Forum Description: Topics on the Avidyne AXP340/322 ADS-B Transponder
URL: https://avidynelive.com/forum_posts.asp?TID=644
Printed Date: 26 Mar 2026 at 4:28pm
Software Version: Web Wiz Forums 12.07 - https://www.webwizforums.com
Topic: New encoder required for 340 install?
Posted By: flybikeski
Subject: New encoder required for 340 install?
Date Posted: 16 Apr 2015 at 6:22am
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I received a quote for a install and the shop said, "you'll probably need a new encoder too" without even knowing what I have. I believe I have an encoding altimeter with grey code. Are folks generally getting a new digital encoder with their installs? Is the digital (RS-232 interface) better in some way to the old grey code? Or does he just want to deal with less wires? (but then he has to tie into the pitot/static system and figure out where to put the unit - I guess no problem for these guys). Thanks |
Replies:
Posted By: edanford
Date Posted: 16 Apr 2015 at 6:57am
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Nope, I had to change nothing from my encoder. ( I had a KT76A transponder) If you have a KT76A, you can pull it out and plug in the AXP340 and it will work mode S. I have a grey code encoder The chassis for the transponder has to be swapped to upgrade to ADSB out for the GPS signal connector but that is it. ------------- Ed |
Posted By: roltman
Date Posted: 16 Apr 2015 at 7:19am
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I had a newer Sandia encoder, but was using the only grey code with my old GTX330. I did have it rewired when I did my 340 install. I don't recall that is required though, maybe for 1090 ADS-B? The Sandia had 2 RS232 and 1 grey code outputs IIRC. I sent the grey code to my STec alt-preselector. I sent one RS232 to IFD540 #1 to have it cross talk to IFD540 #2. I sent the other RS232 to the 340 which has a parrot feature which parrots the output to the MLB100 ADS-B Input. The RS232 is higher resolution. I think grey code is 100' resolution while RS232 can depending on the encoder have 1' resolution. |
Posted By: SB Jim
Date Posted: 16 Apr 2015 at 7:34am
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I had an encoder as well as a serializer (Icarus 3000U?). The serializer was required for my CNX 80 (can't recall why). For unknown reasons the unit would be very accurate at times and 200 feet off other times. I asked my shop to rip them both out and put in one good one. It's been spot on since AFAIK. |
Posted By: flybikeski
Date Posted: 16 Apr 2015 at 7:34am
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Thank you. Yes, I saw the 340 could output and wondered if the 540 could take its altitude information from the 340 via RS232 instead of splicing from grey code. The MLB100 needs altitude? Why? And if it does why can't it get it from the 540 which it is connected to? |
Posted By: roltman
Date Posted: 16 Apr 2015 at 7:59am
I think we chose the AXP340 altitude output because there was another transponder connection needed to be sent to the box. Thinking a little more about it, traffic target adjustments may be the reason for the pressure altitude input. I'm not an ADS-B protocol expert, so take this as a WAG. |
flybikeski wrote:Posted By: Kentucky Captain
Date Posted: 06 May 2015 at 1:29pm
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I received a quote for a install and the shop said, "you'll probably need a new encoder too" without even knowing what I have. I believe I have an encoding altimeter with grey code. When they did the install they left the original encoder in and it worked. Somewhere into the second test flight it decided to give it up and they had to install a new one. Fortunately we were still at the avionics shop and they only charged us for the encoder (no labor). If you have an ancient one like ours was it might be cheaper to replace it now as opposed to later. We did the same thing with the ELT and fuel sending units. We had an old 121.5 elt. A new 406mhz one is under $600 and it was around $400 to install since they had the seats, carpet, and floor panels up. They also had to mount the remote panel for it up front. They were installing a new panel anyway so the costs were minimal. Doing it later would have cost another $1000 in labor. We had a JPI EDM900 installed too and it is very picky about the fuel sending units. We had those rebuilt since they had it all apart. |
Posted By: Paul
Date Posted: 07 May 2015 at 3:07am
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Our plane did not need a new encoder. The old gray code encoder is connected to the AXP 340 transponder. The transponder provides the serial data to the IFD 540 and the Icarus SAM. And we also replaced the ELT with a 406 MHz unit. As long as everything is torn apart and we're spending that kind of money, what's another AU? |