Garmin G3x Wiring Questions

[PapuaPilot]

Happy reading. The GTX45 is certainly different than my GTX23ES.

[PaulSS]

You understood my question\s perfectly. I was assuming the GSU-25 was not needed because I thought WAAS altitude is more accurate than pressure altitude and it seemed kind of silly to provide pressure altitude to the transponder when it already had more accurate altitude provided by the GPS. But sounds like in this configuration its not as accurate so altitude is provided by GSU-25.

Transponders work off 29.92 and then 'fudge' the result to get altitude. It would be no good providing a GPS altitude because (a)they're not as accurate as you think and (b)they're not working off a standard pressure setting, so everyone can be off by varying amounts. So you definitely need to provide your transponder with a pressure-based altitude, instead of GPS-based. Since the EFIS is plumber for pitot and static pressure it's quite normal to just have the transponder 'talk' to the EFIS over the CAN bus and gain the information it needs from there.

[tracstarr]

I currently am installing the GTX45R with the same equipment as you mention. Here's what I have...

GTX45R >>> G3x
30 41
8 24
51 35

GTX45R >>> GSU25
31 9
9 10
52 11

GTX45R >>> GPS20A
29 5
50 6

G3X >>> Artex 345 ELT
48 9

[Shadowrider]

I currently am installing the GTX45R with the same equipment as you mention. Here's what I have...

GTX45R >>> G3x
30 41
8 24
51 35

GTX45R >>> GSU25
31 9
9 10
52 11

GTX45R >>> GPS20A
29 5
50 6

G3X >>> Artex 345 ELT
48 9

That what I am getting also. Only difference is I went GPS-20a to ELT (ACK) via GPS-20A RS232 TX 2 (pin 3 on GPS20).

I also installed the, Made in China, super pain to put pins on, USB cable. Seriously..... can't we just put a USB port on the transponder???

RED pin 44
Green pin 2
WhT pin 24
BLK Pin 45

Interesting side note, I accidentally turn on elt for about 2 seconds. Hurried and called the command center and they said they just saw ELT trigger for a couple seconds. He had me read them my HEX number and it was my ELT. That was in my shop they said they got a hit and next pass of the satellite would have given location. Crazy! I apologized and he thanked me for calling.

[PaulSS]

Thanks for your response. Just for the sake of discussion I thought the WAAS GPS was more accurate then anything? It gives you true altitude very accurate. For example I can get lower on the approach on most WAAS gps LPV approaches than i can via ILS. Vertical guidance is provided by gps alone.

The GPS altitude is certainly getting better day by day and it is, in some cases, super accurate as you say. Regarding the approaches then an ILS may well have higher minimums due to surrounding terrain, strange topography etc, whereas a GPS approach can 'steer round' that terrain and allow for a more customised approach and lower OCL.

The trouble with the transponder using GPS altitude is the standard of GPS used. Some people may have a super-duper all-singing and dancing bit of kit, whereas others may have a cheaper one that doesn't self-check, allow for RAIM outages etc. Many people won't even have a GPS coupled to their transponder. And there's the problem: ATC can't provide separation if pilot A has a magic machine providing extremely accurate altitude information, pilot B has a cheapo GPS chip from eBay and pilot C is still working off static pressure being fed to his encoder. Since we're not there yet with a standardised GPS altitude we have to stick with what is currently in place i.e. every transponder working off 29.92 inMg (1013.25 Hectopascals) to give your flight level and then a 'fudge' calculation made by the ATC machine to provide your altitude (below 18000' in the USA).

As for pins, don't get me started :-) I'd bought loads of Dsubs, pins and the crimping tool only to find 18AWG won't fit and I wasn't happy with cutting of strands of wire to make them fit. SO, I bought another load of Dsubs with solder cups. My soldering is really not very good (although I have got better over the last few days), so it was a struggle trying to ensure pins didn't get soldered together etc. I started with a female Dsub and, looking at the back, the pins run 1 to 9, left to right. All good and soldering done. 3 female Dsubs later and it's time for some male Dsubs. THIS complete idiot assumed the numbering would be the same.......it's not, as most sensible people will know. 5 DSubs male Dsubs later and suspicion is roused by something I read. Damn you to hell Google for revealing my mistake. Shrink tube, solder, wire, molex connectors which looked so neat...........

My top tip is to get a permanent pen and write the numbers on the back and front of every Dsub before picking up the soldering iron

[Shadowrider]

Whats the deal with config module? The little black box smaller than a dime? Why does it have funky pins and how are you suppose to connect them? I can't find instructions in the manual?

[tracstarr]

Whats the deal with config module? The little black box smaller than a dime? Why does it have funky pins and how are you suppose to connect them? I can't find instructions in the manual?

Not sure I know what you are talking about. Do you have a picture?

[efwd]

Interesting. I don't recall ever seeing that but it is likely that when the avionics built my harnesses, they had removed all the connector stuff from my boxes already. The only reason I recognize what it is is because I had to replace mine when Garmin took my radio back to do a software change. When I got my radio back I was instructed to swap this device that was in the connector. Let us know when you figure out where it is to be installed.

[efwd]

I have that very crimper. I works well. Bad thing was, stripping wire that small caused me to have to buy another wire stripper that had that gauge. Back to the device. I don't have anything like that for the G3X. The closest thing I have is the one that goes in my Transponder connector. It was more of a chip encased in epoxy, not black. It does hold information that the transponder uses to identify you to ATC.

[Shadowrider]

I have that very crimper. I works well. Bad thing was, stripping wire that small caused me to have to buy another wire stripper that had that gauge. Back to the device. I don't have anything like that for the G3X. The closest thing I have is the one that goes in my Transponder connector. It was more of a chip encased in epoxy, not black. It does hold information that the transponder uses to identify you to ATC.

hmmm......It shows it in the installation manual and says there is details to install the configuration module in chapter 20 but cant seem to find more info on where this is suppose to mount. I am going to go back and check transponder because I did not see anything like you mention on my transponder. I have the GTX45R.