Cheapest solution for Mode C Transponder and ADS-B?

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Built2Fly

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I am starting a build, and as life goes I am living under the Mode C veil of SAN.

So basically I have two choices. One, making it non-engine-driven-electrical and being exempted. Two, biting the bullet and getting a Mode-C transponder and an ADS-B. I guess in a busy airspace where we are, being seen offers some safety advantage, so I am looking at transponder/ADS-B solutions.

Now the question, what is the cheapest solution to satisfy the Mode-C and ADS-B requirement? Any ideas? How about a used Garmin 327 with an Uavionix echoUAT? All suggestions are appreciated.
 

Toobuilder

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If you do the 327/Uavonics Echo (what I'm running in the Rocket), you still need to come up with a WAAS GPS source. That's a $500 add from Uavionics, but it's still about the least expensive option going. I already had the WAAS GPS (a GTN 650) and the 327, so the bare Echo box was an easy and inexpensive way to go for me. Works good.

I went with the GNX 375 in the RV and it too is great. Main downside is the 1090 ES protocol which removes anonymous mode. If they did a 978 UAT version, that would be the go to box for me.
 
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Turd Ferguson

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I would plan on an "all in one box" solution. When the time comes to pull the trigger you can narrow down to a few specific brands and see what new vs used options are out there.
 

GeeZee

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KT76A‘s go for about $200. Garmin GTX 375s for $250-400. Add a echoUAT with skyfx bundle for $1399. Thats a few hundred less than the tail beacon and you get ADSB IN as well (Saves another couple of hundred putting together a Stratux). It’s UAT so you get “anonymous mode”. Although uavionics anonymous mode is enabled/ disabled using a phone app, which is suboptimal.
 

Daleandee

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KT76A‘s go for about $200. Garmin GTX 375s for $250-400. Add a echoUAT with skyfx bundle for $1399. Thats a few hundred less than the tail beacon and you get ADSB IN as well (Saves another couple of hundred putting together a Stratux). It’s UAT so you get “anonymous mode”. Although uavionics anonymous mode is enabled/ disabled using a phone app, which is suboptimal.
I haven't gotten the bundle yet but I have a Garmin 320A that was gifted from a friend. As mentioned already the Echo bundle with a GPS position source is $1400.00. I have my transponder check due in November and will likely do the ADSB upgrade then.

Another point on the ECHO is that it will transmit ADSB "In" to you EFB i.e. I use an iFly 740b.
 

Jay Kempf

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I have a KT76A. Trying to figure this same thing out. Stratux and Skybeacon seemed the way to go.
 

Daleandee

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I have a KT76A. Trying to figure this same thing out. Stratux and Skybeacon seemed the way to go.
I have a Raspberry Pi "assemble it yourself" version that works well with my iFly 740b for traffic & weather. I understand (if I'm reading it correctly) that the Echo unit shown above will broadcast the ADSB in so that I can remove the Stratux unit so the weight change should be minimal.

The Skybeacon does make life easier as the Echo Bundle unit requires mounting two additional antennas, one above and one below. .
 

Built2Fly

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Thanks, guys. A lot of good ideas.

I have a question on echoUAT. It has an interesting power transcoder feature. There is no connection needed between transponder and the ADS-B unit. The echoUAT ADS-B unit will figure out what you are squawking on the transponder by picking up the fluctuation on the power bus.

That sounds like a neat feature. But how reliable is that? Does it work in real life, or is a RS232 direct line needed? Any experience?
 

TFF

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It gets the signal through the power wire. They have to be on the same buss. On another forum someone had them powered separately and he could not get it to work that way. Finally it got figured out.
 

Built2Fly

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It gets the signal through the power wire. They have to be on the same buss. On another forum someone had them powered separately and he could not get it to work that way. Finally it got figured out.
Does it work reliably once they are on the same bus? I am wondering how well it works, because no additional wire really saves a lot of hassle.
 

rv7charlie

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A heads-up on older XPs. My neighbor does XP certs, and also does ADSB installs. He will no longer do an ADSB install with an older cavity tube type transponder, because they so frequently won't pass ADSB flight tests, and even if they do, they often start triggering FAA letters soon after the initial install. He says that there are no issues with the later all-solid state models like the Garmin 327, etc.

FWIW...
 

TFF

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The flight school here has most of the fleet with them. They had one take on water and give issues, but it was drowning.
 

Toobuilder

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Does it work reliably once they are on the same bus? I am wondering how well it works, because no additional wire really saves a lot of hassle.
I tried mine with 232 from the 650 (GPS position) and the 327 (squawk/altitude). I could not get all the output protocols to talk to everything so I kept the 232 from the GPS and let the Echo "sniff" the transponder. Could NOT get it to work despite having the 232 hooked to the 650 per the instructions. Turns out that particular output on the 650 did not have the correct protocol as an option. So I switched to another serial output that DID allow the required protocol and it started working perfectly. I did my PAPR flight for "score" and the report came back with zero discrepancies. Its been flawless for me so far.

The product is great, the documentation SUCKS.
 

Built2Fly

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@TFF, @Toobuilder, @rv7charlie

Thanks for the feedback. It seems that the echoUAT is a good way to do. I think I'm going to spend a bit more to get a Garmin GTX-327 instead of the King KT-76A. I saw a few cheap used Garmin 327 that pops up for $300-ish. It seems to be reasonable price I can afford.

I am thinking about building a serial altitude encoder. It's fairly simple to make. The only uncertainty is to get it to talk the right protocol for Garmin. I have some documents there.

Is there any recommendation on a cheap GPS source? Does it has to be WAAS for an experimental setup, or anything as long as it is not too badly off?
 

CAVU Mark

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Garmin 327 with uAvionix SKYFix and the box. Only needed to install the GPS antenna on top and the stick and ball on the belly. Now I have IN/OUT with no wires hanging around. Sound installation.
 

Markproa

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Meanwhile, here in Australia, we can use SkyEcho2

 

GeeZee

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Is there any recommendation on a cheap GPS source? Does it has to be WAAS for an experimental setup, or anything as long as it is not too badly off?
It cannot be any old GPS, no matter how accurate. It needs to be one of the approved position sources. Also I bought a used AK350 alt encoder for $30 so probably not worth your time to design/build/test one.
 

edwisch

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There's a reason that some avionics have to be approved and tested at whatever level, even in an experimental. Things like transponders and comm radios have to work within the system cooperatively, so that, say, the transponder meets the requirements of the whole systems, and so that the comm radio doesn't screw things up for somebody else. In contrast, if you do your own ignition system and it fails, that doesn't affect anybody else. If your altitude encoder is off, that could cause ATC to not provide good traffic separation services to *other* aircraft because your plane isn't at its reported altitude.
 

BJC

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It cannot be any old GPS, no matter how accurate. It needs to be one of the approved position sources. Also I bought a used AK350 alt encoder for $30 so probably not worth your time to design/build/test one.
I find performance criteria in the regulations, but not a list of “approved position sources”. Can you provide a link to that requirement and list?

Thanks,


BJC
 

FinnFlyer

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Yes, the echoUAT + FYX GPS package still appear to be the cheapest solution. And with free ADS-B in.

Do you have a serial altitude source, like from a Dynon D-10? I made a serial to Gray converter using a $6 Arduino Nano. Digital outputs connected directly to the GTX320A. (Does need a level shifter from RS-232 to 5V -- I'm using a 2N7000 FET.) I'll post the Arduino code if interested.

Finn
 
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