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Garmin GTX 327 question

jthocker

jthocker

Well Known Member
Maybe Stein can answer this.
My 327 transponder is getting RS232 Data from both my Dynon D180(ch 1) for the encoder, and from my 496 (ch 2) for groundspeed.
The encoder works like a champ. The unit goes from standby to ALT automaticly but does not "appear" to go into standby on the ground after the default 24 seconds of zero groundspeed.

Ch 1 is set to Icarus Alt
Ch 2 is set to GPS
Autostandby is ON
Squat swiches OFF

Am I missing something.
 
I may be wrong, but I don't think the GTX 327 knows how to listen to the NMEA data format that's spit out by the 496.

mcb
 
Matt
I don't know which part of the stream it might use but it does use GPS groundspeed to auto turn on/off.
 
Go to the serial data viewing page (3.3.8 page 31 in the install manual) and see if your recieving the GPS data, if not, I suspect the wrong format or baud rate being output by the GPS or a wiring error.
 
Thanks for the suggestions guys, but the wiring is correct and the baud and format is correct(Aviation and VHF) on the 496. SL40 loads frequencies from the 496, Dynon gets gps data from 496, and 327 goes from stby to Alt via gps data from 496. ALL OF THIS STUFF IS WORKING CORRECTLY!!
After shutdown at the hangar the transponder still says "ALT".
I'm wondering if there is a bug in the transponder software and it needs to be updated.
 
Mine has always done the same thing Jon - it automatically goes to "ALT" when I launch, but I have to manually take it to STBY afer taxiing clear of the runway. It's on my checklist, and part of my routine cockpit sweep, so I have never gotten up the gumption to figure out if I can make it do it by itself....

Paul
 
Same thing

Mine does the same thing. It is wired and programed correctly. I do like Paul does and manually go to STBY after landing. Always goes to ALT automatically when I take off.

Be interesting to see if there is a fix. The book says it's supposed too.

Ted
 
Mine works

Make sure you have the wiring correct per the drawing in this thread. Then make sure you are outputting "Aviation Data" to pin #2. Then make sure the unit is configured correctly. Newer units are able to transition to ALT using the change in pressure altitude so if they are not getting Aviation Data and cannot see the speed transition, they can toggle to ALT but will not toggle back to STBY.
 
Hi John,

I don't acutally have any better answers for you than anyone else. Mines running off of a 430 so I don't have a good comparision. Let me do some quick homework and see.

Cheers,
Stein
 
Wiliam
I am getting Aviation and VHF data to pin 2 from the 496.
I will check the firmware tomorrow though.
Thanks
 
jthocker said:
Thanks for the suggestions guys, but the wiring is correct and the baud and format is correct(Aviation and VHF) on the 496. SL40 loads frequencies from the 496, Dynon gets gps data from 496, and 327 goes from stby to Alt via gps data from 496. ALL OF THIS STUFF IS WORKING CORRECTLY!!
After shutdown at the hangar the transponder still says "ALT".
I'm wondering if there is a bug in the transponder software and it needs to be updated.
Click to expand...

I see the problem now. When the 496 is configured "Aviation and VHF", that is "Aviation IN" and "VHF Out". The 327 needs "Aviation Out" from the portable which Garmin portables will NOT send. Mine works because I have it wired to a GNS-430. Since it cannot understand the "VHF Out" data, it uses pressure altitude for the transition TO ALT but will NOT transition back.
 
Thanks Stein
On my RV6 I had a 430 and 330 and I never touched the transponder, it turned itself on and off. It's kinda like having a car with auto headlights and then getting a new one without, I'm always forgetting to turn them off.
 
William and Brian
I am at work and don't have my 496 or the manual with me, but as I recall the choices for Garmin Data Transfer are "Aviation", and "Aviation and VHF"
among others. You select Av. and VHF if you have an SL30 or SL40 hooked up to the 232 output from the 496. I believe both settings output Aviation data, with the VHF setting also outputting frequency info. Anybody out there with a 396/496 unit or manual laying around to confirm what the available options are on the setup page. I'm going from memory and what I believe to be true.

If all my 496 was outputting was VHF frequency info I don't think my Dynon HSI would be guiding me so well.;)

But tomorrow I will experiment, thanks for the input!

Well after downloading the 496 manual the options are, TIS or Aviation IN /and NMEA ,or NMEA and VHF out. Aviation In is for crossfilling from a 430 to the 496. TIS is info from a 330 transponder to the 496.
Sorry guys I have it set correctly.
 
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NMEA is very different than AVIATION and AVIATION is what the transponder wants to see. Don't think it will work with it set to NMEA, looks like your out of luck unless you have another GPS that you can feed it AVIATION data from.


jthocker said:
Well after downloading the 496 manual the options are, TIS or Aviation IN /and NMEA ,or NMEA and VHF out. Aviation In is for crossfilling from a 430 to the 496. TIS is info from a 330 transponder to the 496.
Sorry guys I have it set correctly.
Click to expand...
 
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Firmware

Brian
Are you talking about the transponder firmware?
I flew this morning and checked different settings.
Existing settings were: 496 Aviation In/ NMEA and VHF out
327 As previously said above
Everything works well, but when viewing the transponder data screen I see GPS but don't see any groundspeed.

So it looks like you're right Brian, the transponder wants RS232 data in a format thats unavailable from the 496 on channel 2.

By the way I checked all the obvious 232 outputs from the 496 while in flight and nothing showed up on the transponder and other outputs screwed up the Dynon.
 
Brian
Thanks! I was on hold with Garmin until I had to leave for work this afternoon before I could talk to someone about the firmware. I guess I'll have to hold a little longer next time.
Regards
 
Firmware update

I flew today with Scott Hersha, we have identical setups 496 feeding Dynon D180's and 327 Transponders. His 327 is fresh from Garmin with the latest frimware 2.10, mine has 2.09. Both transponders go to ALT from STBY via press. alt and will not go to STBY on ground. On the rs232 viewing screen we both confirm press. alt on Ch 1 and on Ch 2 we show GPS selected but no GPS data, i.e. GS, Lat/Long, or track. Called my local avionics shop because I was on hold to Garmin for at least 1/2 hour, and he can get right thru. His answer from Garmin is....... NO TSO'D PANEL MOUNT UNIT WILL ACCEPT DATA FROM A NON TSO'D OR HAND HELD UNIT PERIOD! You can go the other way with Data, hence 430 loads flight plans to 496 or 330 TIS loads to 496.:(
My Avionics guy said there might be a workaround using an external switch that the 327 will accept and that would be an airspeed switch that goes to ground via pitot pressure. :)
Stay tuned.
 
Do you have more options on the Dynon side? Maybe they can output different protocol that would give the 327 needed info.

All I can tell you is that I'm feeding mine from my GRT EFIS and it works fine (confirmed on Saturday) and it's probably just the message type that the EFIS is sending... It'd probably be easier for Dynon to do a software change than messing with external switches and pressure sensors.. But I'd check with Dynon first in case they already have that capability..
 
Radomir
Whats feeding your GRT? Is it a 430 or 396/496? If you have a 430 then you have apples and I have oranges. If you have 396/496 then maybe your GRT can convert NMEA to Aviation, I doubt the Dynon does this, but I could be wrong.
Regards
 
It's neither :) It's a built-in GPS that GRT offers.. However, I'm not sure that it matters.. It's all about what EFIS sends to the transponder.. GRT sends what they call FADC with ALT message (fuel air data w/ alt)... I don't know the details of this particular protocol, but apparently it has enough data for 327 to determine when to start squawking and when you landed.. In other words, I don't think this is either NMEA nor Aviation (as you'd think in terms of GPS protocols..)

I see no reason why Dynon would not be able to do the same... this stuff is as easy as it gets in terms of software.. (they may be doing that already.. not sure if dynonsupport can chime in w/ more details..)

EDIT:

GRT sends FADC (Z format) to 327. You set 327 on "Shadin FADC w/ ALT" (not Icarus!).... this FADC (Z) message contains Fuel flow, fuel totalizer, airspeed, and altitude
 
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Update

I got my transponder check done today and talked about autostandby with the shop boss. He said I should just put in a pressure switch and be done with it. He said they use them all the time and the transponder is very easy to program with a........MPL503 pressure swich.
Pitot...In, Static....In, 2 contacts, 1 to ground, 1 to pin 22 on GTX 327.

I found the switch here for 9.95, but they have a minimum 15.00 order, so I bought 2, lots of 327's around here.
Here's a link for the switch:

http://www.electronicsurplus.com/ccp74190-pressure-sw-11-5-inches-water-adjustable-mpl503-13671.htm
 
Auto Standby works now

I just installed my pressure switch today. A tee in the pitot line, a tee in the static line, 2 wires with mini fast-ons to connect to the pressure switch(1 to pin #22 on the 327, the other to GND).
Setup menu on 327..........autostandby---ON, Squat switch---YES, sense---HIGH.

Test flight result............SUCCESS!!
Transponder now goes into ALT by itself, and goes to STANDBY by itself.:cool:
The geek in me is now satisfied. If a feature is available I want it to work!
 
Why turn to standby?

Since I have been flying my RV7A I have just left my 327 turned on to ALT all the time. Why do you need to turn it to standby? I'm guessing that you need to, on an airport with a tower, I'm on an uncontrolled field.
 
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One reason...

Because it is a nice thing to do for others. For example, if someone else on your field has Skywatch or some other traffic detection device it can issue traffic alerts for the plane near it, whether your on the ground or in the pattern. There have been times I turn my traffic audio off in the pattern because ground aircraft cause traffic alerts at high workload times, like on short final when the altitude difference gets inside the threat warning window.

That said, I have to admit I often leave mine on all the time, so I have no reason to judge anyone :eek:

bhester said:
Since I have been flying my RV7A I have just left my 327 turned on to ALT all the time. Why do you need to turn it to standby? I'm guessing that you need to, on an airport with a tower, I'm on an uncontrolled field.
Click to expand...
 
bhester said:
Since I have been flying my RV7A I have just left my 327 turned on to ALT all the time. Why do you need to turn it to standby? I'm guessing that you need to, on an airport with a tower, I'm on an uncontrolled field.
Click to expand...


What you are doing by switching to stby is to make certain your transponder will not reply to side lobe signals. There is a side lobe suppression circuit in your transponder, but if it is acting up the controller can get erronious or multuiple targets from your transponder. If you want to read about the pulses and how it works just search "Side Lobe Suppression" and you will find many explanations of what is happening.
 
GX-320 models...

rwhittier said:
Because it is a nice thing to do for others. For example, if someone else on your field has Skywatch or some other traffic detection device it can issue traffic alerts for the plane near it, whether your on the ground or in the pattern. There have been times I turn my traffic audio off in the pattern because ground aircraft cause traffic alerts at high workload times, like on short final when the altitude difference gets inside the threat warning window.

That said, I have to admit I often leave mine on all the time, so I have no reason to judge anyone :eek:
Click to expand...

...could be set up this way if the pressure switch was NC (Normally Closed) at zero pressure.

It would only involve a single wire to the < Pin 16 - External Standby > conection.

This would give the mechanically set 320 models the same "auto stand-by" functionality as the digital 327 models.
 
A little clarification please..

Just finalizing my wiring for the 327. I have the Dynon 180 going to Pin 19. After reviewing this thread, do I even bother running the 496 data out to Pin 22 or does it matter?

I have the data out running already to the D180, but can splice it to the Pin22 of the 327 if it does use the ground speed from the 496??

Any help much appreciated.

Thanks


Don
 
I'd say don't bother. Since this thread was posted, the FAA has changed their mind. The (relatively) new AIM recommendation is to run the transponder on ALT all the time, even on the ground, unless otherwise directed by ATC. Of course in the air in controlled (A-E) airspace it's required. I just leave mine on ALT all the time now.
 
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