What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Upgrading my panel for WAAS

DylanRush

Active Member
In my RV-6A I currently have:

Dynon Skyview Touch
Apollo GX55
Val nav 2000
GRT Mini X
Garmin gtx 325 transponder (mode C, not WAAS)
U avionics ADSB. It’s not a beacon, may be an Echo UAT?
Two axis autopilot slaved to the dynon - forget the make
A thin com next to the Val nav

Picture of my panel here:
ETRvrcq_d.webp


I want to be able to fly LPV approaches so I’m thinking of three options:

1. Replace GX55 with Garmin GPS 175- $4300 plus labor. Would I have to run a new GPS antenna for this?

2. Replace GX55, transponder, uavionics with Garmin GNX 375. $8000 plus labor, but I could sell the adsb and transponder. Might be able to keep the GPS antenna?

3. Replace GX55 and maybe nav/com with GTN 650. $10000 plus labor

Right now I’m leaning towards (2) because it seems like the simplest in terms of wiring everything together. I’ll likely do the labor myself.

What do you all think? Thanks in advance.
 
Last edited:
Just some thoughts
1. You say your current transponder is a mode C 375. That must be a typo
2. Be aware that used mode C transponders have flooded the market. You won?t get more than $400 for one (your option 2).
3. Most new gps boxes require an antenna which has its own built in amplifier which is likely unique to that box. e.g., plan on a new antenna with any new gps. If the coax is RG400 or equivalent you can re-use it - but you may need new connectors.
Your option 1 will get you what you want at the lowest cost.
 
As Bob said, you'll need a new WAAS GPS antenna, because your current antenna is non-WAAS.

All three options will also require a Dynon ARINC-429 box to feed data to the Skyview and AP (if not a Dynon AP, which would take its feed from the Skyview).
 
Awesome thanks friends. The echo UAT is paired to another GPS, probably a SkyFX. So I may be able to toss or sell that as well and have the 175 feed the echo UAT position information.

The Dynon can already talk to my GX55 so it has some sort of data link already. May already by an ARINC-429?
 
Awesome thanks friends. The echo UAT is paired to another GPS, probably a SkyFX. So I may be able to toss or sell that as well and have the 175 feed the echo UAT position information.

Maybe, maybe not. Garmin GPS boxes send out ADSB data via RS232 using a proprietary protocol, "ADSB+" (or maybe it's ++ now, not sure). Some third party boxes can read it, some cannot. I don't know about the Echo.
 
So I've been researching this for a little while now and I think I'm ready to do it myself, although I have an avionics shop on standby to help if I need it. I have a GPS-175 installation kit and an SV-ARINC-429 (ARINC-429 adaptor for SkyView). I'm handy with hobbyist electronics but I've never done anything with avionics before.

Here is my panel:

HNhZt9sh.jpg


The GX55 which I plan on replacing is at the top. To get to the sides of the mounting tray, I can remove the SkyView, the airspeed indicator, and I believe also the GRT (although I haven't tried removing the GRT yet, didn't have torx bits handy.)

With the SkyView removed:

DeYCCqkh.jpg


There are a couple decades of upgrades going on in here. It looks like a SkyView Network splitter (SV-NET-SPL) was used as a connector between the SkyView and the EMS. I plan on using the male D9 connector that's been taped over (highlighted) using a SV-NET-8 female-female cable to the SV-ARINC-429.

Some more views of the GX-55:

YDPaXZ6h.jpg

UfviMhth.jpg

LllViiLh.jpg


I was scratching my head for awhile trying to figure out how to remove the GX-55 from the tray. The instruction manual referred to a 3/32 hex locking screw. Is it accessible through this little hole on the front face? It looks like that's how the GPS-175 locks into its tray. Could I use the same 3/32 hex tool to lock/unlock both units?

6dLGbvqh.jpg


Here's my wiring diagram:

xP6BiI3h.jpg


This is the view from behind my airspeed indicator, showing what I believe are the screws and nuts affixing the GX-55 mounting tray to my panel:

oYsOzrYh.jpg


So anyway my overall plan is:

1. Assemble the wire between the ARINC-429 adapter and the GPS-175
2. Assemble the bracket, back plate, config module for the GPS-175
3. Remove the Apollo GX-55 from the tray
4. Somehow remove the GX-55 mounting bracket. I believe that by removing my SkyView, airspeed indicator and GRT I should be able to at least hold on to the nuts, and unscrew from inside the tray
5. Install the GPS-175 bracket in the same place. Bring my new ARINC-429 cable up through the rear, and connect the coax to the rear as well. The connector may be different, need to research this.
6. Replace the GX-55 antenna with the new one. These have the same dimensions, should be easy.


Please let me know if any of these assumptions are false:
1. The existing coax has the right shielding and resistance. If this is not the case, I believe I would see it in a diagnostic check. If I need to replace it I am hoping I could simply tie a string or wire to one end and start pulling on the other, pull the old one out, letting the string occupy where the wire used to be, then using the string to feed in a new wire. That sounds silly typing it out :eek:
2. The screws to mount the old and new trays have roughly the same spacing.
3. The GRT can be removed as easily as the SkyView
4. I can simply clip away the serial RX/TX wires from the SkyView to the GX-55 as they are no longer needed


What kind of wire should I use to construct the ARINC-429 cable? Does it need to be shielded? Where is the best place to get it?
 
Last edited:
Unless you have specialized equipment you can’t tell the quality of the coax with just an ohmmeter. Look for ‘RG-400” printed on the cable.
Do not throw away the RS232 connection between the gps and efis. You’ll need it, different data goes thru rs232 and arinc, you need both. You also need a second rs232 connection, from the gps to the adsb-out, assuming it can read Garmin’s ADSB+ format. I suggest connecting all RS232 ports to short wires now, will save effort if you need them later. Get a d-sub crimper, regular and high density, for crimping the pins. Stein sells an inexpensive one that works.
If you can pull the coax then it was never installed properly. It should be supported by Adel clamps, zip ties, lacing cord, etc, every 6-10” or so. Same for any new stuff. The screw holes for the new tray may, but most likely will not, line up with the old holes. Be ready to drill new ones as needed. For this short run you can likely get by with just a twisted pair for your arinc cables, e,g., two 20 gauge insulated wires, twisted together along their whole length. If possible use two different colors, if not, use an ohmmeter so you know which is going to A, which to B. Don’t get them confused. More deluxe, buy some shielded twisted pair cable. Connect the shield to ground at one end only.
Edit. Yes, disconnect the rear wires, unscrew the four allan or torx screws, the Grt should pull out of the panel.
 
Last edited:
Do not throw away the RS232 connection between the gps and efis. You’ll need it, different data goes thru rs232 and arinc, you need both.

Are you sure? All of the instructions I've seen so far have RS232-1 TX coming from the GPS going to the SV-ARINC-429 module. So the SV-ARINC-429 module will handle both ARINC communication with the new GPS as well as receiving serial data from the GPS. I haven't seen any evidence that I need to connect the RS232 serial from my GPS directly to my SkyView's D37 harness. I am thinking of throwing away the existing serial connection directly from the SV-HARNESS-D37 to the GX-55.

And do I need ADSB+? I'm already ADSB in/out and already see traffic on my Dynon through my existing ADSB rig, GRT Safe-Fly WAAS -> Echo UAT -> Dynon, GRT. I suppose I could remove the GRT Safe-Fly and replace it with the GPS-175 ADSB+ to my echoUAT.

Edit: And thanks so much for your help so far Bob!
 
Last edited:
If you already have a gps source for your adsb, then you’re good to go.
If you run the rs232 line to the dynon external module instead of the box itself that should be okay too. As long as the data can find its way to the efis.
 
Here is my wiring diagram for GPS 175 to SkyView

Dylan,

He is a copy of my wiring diagram for SkyView to GPS 175, with both the SkyView and GPS 175 settings. If you decide to go with the GNX375, I can update this to the GNX375 in a short time. Let me know.

The GPS 175 and GNX 375 is the same height as the GX55, so it should be a really easy swap out. The GNX 375 is deeper(longer). As for the transponder, just add the Dynon 261 transponder. You will be less than the $8000 for the GNX375, and you could open up a little panel space.

Brian

Yea, I finally made the front page. ;-)
 

Attachments

  • GPS 175 to Dynon SkyView System With Config.pdf
    262.8 KB · Views: 508
Last edited:
Awesome thanks Brian! I am finally putting this together, hopefully this weekend or next week!

Looks like the existing cable is RG-58 so I will have to buy some RG-400 and route it. It actually doesn't look to hard to route, just need to bring it next to the passenger seat and behind the baggage compartment. I am thinking of buying 20-25 feet and cutting off what I don't need.

I am planning on just keeping the existing GTX 325 transponder in there.

For wiring I am thinking of just using unshielded 22 gauge tefzel M22759/16 for both power and data. The connection between the ARINC-429 adaptor and the SkyView won't be shielded anyway.

Do I need a $300 crimper or should I just get a $30 from Amazon?

Do I need to seal the GPS antenna to my empennage with anything or just screw it on?
 
My continued thoughts

Dylan,

Per the install manual, use 22 gage wire for all the wires needed between the GPS175 to the ARINC429 module, and the power and ground. They don’t need to be shielded. The wires for the data should be less than 2 feet.

The GPS has an o-ring on the base of the connector, so just use screws to mount. No sealant needed.

The $300 crimper is up to you. See if you can borrow one. If you are going to do more later, then pick one up on eBay between $100 to $150. Look for the proper positioners also. You need the following positioners, K41, K42, and K13-1.

Good luck on your install.

Brian
 
The less expensive crimper from Stein works okay. Get the d-sub and high density adaptors. If your transponder is also using RG58, this might be a chance to replace it with RG400..
 
I think I’m almost done save this last step. I’ve routed the RG400 and hooked up the SkyView, etc. only problem is the unit won’t power on. I’ve tested the power and ground pins coming through the backplate connector and it’s showing 12v. The unit powered on at home with the same harness.

It’s possible that it’s not making a complete connection with the backplate. I can only use the locking cam correctly if it’s adjusted towards the rear, thus giving more room between the LRU and the backplate.

I am wondering if I should try trimming some of my panel to make it fit a little more snug...

I’m gonna take it home and see if it still works on my bench. The instructions said to put some load on the antenna, should I just put a 1K ohm resistor on there or something?
 

Attachments

  • 1FE44650-0B7B-4465-B5E3-2D19AD9FFA7C.jpeg
    1FE44650-0B7B-4465-B5E3-2D19AD9FFA7C.jpeg
    64.7 KB · Views: 173
  • 65416000-44AC-4B8E-BF48-B76E36122406.jpeg
    65416000-44AC-4B8E-BF48-B76E36122406.jpeg
    339 KB · Views: 178
Last edited:
Move the panel tray out

Dylan,

From the picture of the panel, it looks like the tray is a little to far back. The side tabs on the lower sides should be a little in front of the panel. The main level of the tray should be even with the front of the panel. When you slide in the unit into the tray, the bezel is stopped at the front of the panel, and the unit can not go down and plug into the connector.

There is two options, move the tray out, or trim the panel so the bezel can move back. It is easier the move the tray out. You might need to move it out about 1/16 of an inch. You should have the flat spots above those side taps on the side even with the outside of the panel. If you pull out the tray, slide in the GPS, and tighten. Mark the back of the bezel on the side of the tray, and that mark should align with the front of your panel. That will give you the best seating of the connector, and the bezel will be flush with the panel.

Brian
 
Last edited:
It’s possible that it’s not making a complete connection with the backplate. I can only use the locking cam correctly if it’s adjusted towards the rear, thus giving more room between the LRU and the backplate.

The instructions said to put some load on the antenna, should I just put a 1K ohm resistor on there or something?

You should be able to slide it into the tray pretty easily, engage the cam, and then screw or tighten the cam and let it pull the unit fully in.
You’d like the dummy antenna load to handle 5 watts at about 50 ohms, e.g., ten half watt, 470 ohm resistors, all in parallel.
 
You should be able to slide it into the tray pretty easily, engage the cam, and then screw or tighten the cam and let it pull the unit fully in.
You’d like the dummy antenna load to handle 5 watts at about 50 ohms, e.g., ten half watt, 470 ohm resistors, all in parallel.

The unit tests fine on my bench, so it must be my panel. It sounds like I need to expose the lips of the mounting bracket... this will be fun, I guess I should just dremel it away.
 
Dylan,

From the picture of the panel, it looks like the tray is a little to far back. The side tabs on the lower sides should be a little in front of the panel. The main level of the tray should be even with the front of the panel. When you slide in the unit into the tray, the bezel is stopped at the front of the panel, and the unit can not go down and plug into the connector.

There is two options, move the tray out, or trim the panel so the bezel can move back. It is easier the move the tray out. You might need to move it out about 1/16 of an inch. You should have the flat spots above those side taps on the side even with the outside of the panel. If you pull out the tray, slide in the GPS, and tighten. Mark the back of the bezel on the side of the tray, and that mark should align with the front of your panel. That will give you the best seating of the connector, and the bezel will be flush with the panel.

Brian

Hey Brian just saw your message too. Currently the side tabs are against the instrument panel. I brought the tray in from behind the panel (from towards the nose of the plane). I don’t believe it’s possible to bring it forward any more without cutting the panel.

I’m either going to cut the panel just enough to bring the tray out 1/16th of an inch, or, going to cut the panel enough to be able to fit the GPS into the tray where it’s seated now. I am worried about bringing it forward without compromising the four holes that I have to mount the tray to the panel, although maybe it’s OK if they are elongated a little bit
 
Tray

Dylan,

Make the holes on the side brackets elongated towards you, so you can bring the tray out towards you. I would guess about 1/16 would work, but check it out the way I suggested. Remove the screws, and slide the tray towards you. Insert the GPS and secure, then put a mark on the outside of the tray where the back of the bezel is, remove the GPS, and then align the mark on the side of the tray with the front of the panel, and you should be good on the depth. Then remark the mounting holes and then elongate the mounting holes to your new marks. Insert screws and tighten. You might be better to use screws and nuts with star lock washers on the nut side to prevent the tray from moving.

Re insert the GPS and check it out. You should be good to go.

Good luck, and it should be easier than it sounds.

Brian
 
Success!

Success! I have everything put together and my GPS is getting a signal and talking to my Dynon �� I didn’t get a chance to fly yet but everything seems in order.

The slot was slightly too narrow to bring the tray any farther foreward, so I trimmed the bottom lips off of the tray. This allowed the top lips to come forward and be flush with the rest of the panel. Elongating the panel holes was a non issue.

Thanks again Brian and Bob for your help.

I am also considering giving the GPS a dedicated circuit breaker because the GRT and echo UAT already occupy the one I’m using. But everything should work fine for now.
 

Attachments

  • 891977C6-AE34-4651-A3E3-649BB7BEB539.jpg
    891977C6-AE34-4651-A3E3-649BB7BEB539.jpg
    362.5 KB · Views: 186
Last edited:
Glad to hear you got it working

Dylan,

Without being there and seeing exactly what was causing the hang up, I can just explain as best I can on how to fix the problem.

I am glad to hear you got it up and running. Thank you for the follow up that it is working.

You will really like the unit.

Brian
 
Back
Top