VAF Forums

VAF Forums (https://vansairforce.net/community/index.php)
-   ADS-B (https://vansairforce.net/community/forumdisplay.php?f=113)
-   -   Advice on ADSB transponder (https://vansairforce.net/community/showthread.php?t=143982)

Ben Meyer 11-23-2016 09:59 AM

Quote:

Originally Posted by BobTurner (Post 1128906)
So does the TT31 auto switch from ground to air mode (based on GPS ground speed?)? Automatic switching of some sort is required.

Been there. Done that.

My installer would not do my install without the speed switch.
Also, make sure the Trig has the latest software. You have to change out the tray but the KT76 connector plugs right up. You will need additional wiring to your position source, RS232, etc. The Trig cuts down on install costs, but there is additional work to do.

Good luck

Ben Meyer

RV8iator 11-23-2016 01:31 PM

Quote:

Originally Posted by jpowell13 (Post 1128790)
Because of Navworx's problems think I'll go ahead and buy a Trig TT31 to replace my King 76A. It's supposed to slide into my existing tray. I'll use my Garmin 400W for the GPS source and my ilevil/iFly combination for ADSB-in. I understand there is an airspeed switch that has to be purchased, but with the rebate, and self install I should be less than $2000 out of pocket. John

It will slide in and work as a regular transponder. If you want to use the ADSB mode S function you will need to wire it to an approved GPS, i.e. 430/650...

To do this you will need to install the Trig mounting tray. The KT76 tray has a large 36 pin I believe, connector and the new tray has two connectors. It's easy if you are comfortable with wiring. If I remember correctly, I just moved the KT76 plug no the back of the Trig tray and wired the GPS into the new 9 pin plug required on the Trig. Look at their manual and you will understand all this.

Mine does not have a speed switch and it works perfectly. Up and running for over a year with several reports from the FAA to verify various settings.

So, it's true it is a plug and play with the KT76, but not true to get the ADSB function you are looking for.

Hope this helps.

Isaac 11-23-2016 03:24 PM

RE:TT31 "Speed Switch"
 
The Trig TT31 install manual contains the following info:

12.4 Automatic Air/Ground Determination
The TT31 can report ADS-B surface and airborne messages. The ADC or squat switch inputs can be utilized to determine air/ground status.....

I didn't find anything in the TRIG install manual that specified that a speed switch was required but it does mention that an airspeed switch can be used in lieu of a Squat switch to indicate on ground status. Recently, I have noticed several people reporting getting "Air on Ground Faults" in their ADS-B performance report from the FAA, so the transponder does need something that it can use to determine air/ground status.

For basic altitude reporting with a Mode A/C transponder you all ready have the transponder connected to an altitude source for pressure altitude either parallel Gray code or an ADC RS232 serial output. If you have Dynon, GRT, AFS, Garmin or similar EFIS in your aircraft you are most likely providing the transponder with altitude info via an RS-232 ADC ouput from the EFIS which contains 'airspeed' data. Per the install manual the TRIG 31 will use airspeed data from the ADC input to determine air/ground status so a dedicated squat switch or airspeed switch would not be required.

jpowell13 11-23-2016 08:31 PM

Amazing what you learn from experienced hands on this site. I was wondering how my existing tray could work even though Trig add says it does. Now I know the truth. Still, seems like the least painful option to get ADSB-out. John

BobTurner 11-23-2016 09:09 PM

Quote:

Originally Posted by Isaac (Post 1129001)
. Recently, I have noticed several people reporting getting "Air on Ground Faults" in their ADS-B performance report from the FAA, so the transponder does need something that it can use to determine air/ground status.
.

I have been checking this out lately. It seems the FAA test specs are pretty stringent. If I land and immediately brake to get below the airspeed where my transponder goes to ground mode, I pass the 'air on ground' test. But if I let it roll at some moderate speed above the switch point, down the runway for 30 seconds or so (fuel tanks are near the far end) then I fail the above test.

Canadian_JOY 11-23-2016 09:29 PM

The Trig TT22 installation manual, by contrast, has very little detail on its "Squat Switch" input, other than to say it is programmable for active high or active low and that if no switch is present the transponder must be configured to disregard this input.

As such, I would be interested to know how the TT22 fares in the FAA "air on ground" test. Anybody out there with experience who would care to share it, please?

Walt 11-23-2016 10:16 PM

Quote:

Originally Posted by RV8iator (Post 1128973)
It will slide in and work as a regular transponder. If you want to use the ADSB mode S function you will need to wire it to an approved GPS, i.e. 430/650...

To do this you will need to install the Trig mounting tray. The KT76 tray has a large 36 pin I believe, connector and the new tray has two connectors. It's easy if you are comfortable with wiring. If I remember correctly, I just moved the KT76 plug no the back of the Trig tray and wired the GPS into the new 9 pin plug required on the Trig. Look at their manual and you will understand all this.

So, it's true it is a plug and play with the KT76, but not true to get the ADSB function you are looking for.

Hope this helps.

Well you 'can' use the new tray and the additional plug provided or you can use the original 76A tray and wire the GPS to the serial port provided (pin 7)on that plug, the additional plug gives you some extra options for RS232, audio and ARINC, but it is not required.

And just to clarify, the TT31 will slide into a KT76A rack only, not a straight KT76 which has a different connector.

Quote:

Originally Posted by jpowell13 (Post 1129087)
Amazing what you learn from experienced hands on this site. I was wondering how my existing tray could work even though Trig add says it does. Now I know the truth. Still, seems like the least painful option to get ADSB-out. John

Hate to say it but its also amazing how much misinformation is available.

BobTurner 11-23-2016 11:07 PM

Quote:

Originally Posted by Canadian_JOY (Post 1129098)
The Trig TT22 installation manual, by contrast, has very little detail on its "Squat Switch" input, other than to say it is programmable for active high or active low and that if no switch is present the transponder must be configured to disregard this input.

As such, I would be interested to know how the TT22 fares in the FAA "air on ground" test. Anybody out there with experience who would care to share it, please?

I have a modified TT-22 from GRT, where the GRT HX provides the control link instead of the usual small panel box from Trig. A Garmin 420W provides RS232 'ADSB+' data to the remote transponder. GRT sent me new HX software so it sends a software signal to change from air to ground mode as indicated airspeed drops below 30 kias.
As I note in previous posts, I pass the FAA tests as long as I promptly brake on landing. If I let it roll at a modest speed (like 25 knots plus a 10 knot headwind) for 30 seconds or so, then I fail the air-on-ground test. It seems that the FAA test is overly demanding on this spec.
Edit added: So obviously it is possible to switch with software, but I know of no open source for it. If you can somehow rig a 'weight on wheels' switch, that clearly is a straightforward path forward.

Canadian_JOY 11-24-2016 07:09 AM

Bob - thanks for sharing this info. When you say the GRT sends a software signal to the TT22, is this being done across the TT22 control lines (TMAP signals), or is this new GRT software triggering a discrete output from the HX to drive the Squat Switch input on the TT22? If I'm interpreting your words correctly, I think you're saying the GRT HX is sending "on ground" in digital format across the TMAP control lines, and that the TT22 is able to strip off these "on ground" data bits and use them to trigger an "on ground" response from the transponder.

If this is the case I'm a bit bummed since I went with the TC20 control head for the TT22 as a means of making IFR certification a bit easier (must use a TSO'd altitude encoder here). Now it seems I'll have to consider wiring in an airspeed switch or something similar in order to achieve ADSB certification. Isn't it wonderful how a regulatory body can make compliance with their regulations more difficult?

Canadian_JOY 11-24-2016 07:29 AM

OK, now I get to show the world how dumb I can be...

As it turns out, I found in my email records a brief discussion with the support folks at Trig (who, by the way, provide excellent support!). I had noticed the need for the squat switch in the TT31 STC and asked if it was required for the TT22/TC20 combo. Below is the response I received. Yeah, you guessed it, I filed it away in my records and forgot it. DOH!

"Having spoken to our STC expert, I have a small correction to make. You only need a second air/ground determination solution if you use an ADC, because apparently they are too unreliable. So using GPS ground speed alone is actually ok. "


All times are GMT -6. The time now is 08:43 AM.