Garmin GDL 82 advice needed

FastEddieB

FastEddieB

Touchdown! Greaser!
Joined
Oct 14, 2013
Messages
11,563
Location
Lenoir City, TN/Mineral Bluff, GA
Display Name
Display name:
Fast Eddie B
I’m about to pull the trigger on this unit for my Sky Arrow. I’ve had good luck with Garmin in the past, and it will pair with a Garmin GTX 327 transponder.

Installation looks pretty straightforward. I have room under my seat for it, and I can piggyback off my existing transponder breaker. So all I need is that 14v source, ground and a short piece of coax to run from the unit to the existing transponder antenna. I should be able to mount the GPS antenna on my glareshield where it will have a great view of the sky.

Two questions...

1) It’s offered with either “10 FT Harness” or “Custom Harness”, as seen here:

49164507116_6b376c21c3.jpg


The former is in stock, the latter is not and adds about $50 to the cost. All my wiring distances are well short of 10’. Can I just go with the former?


2) Has anyone programmed theirs with a Mac, or do I need to find a friend with a Windows laptop.

Thanks, and let me know if I’m missing anything.
 
10 ft. should be fine, just make sure the harness has the ANON and Fault wire included, if that's important to you (just ran into one of their harnesses for another item that left out a few wires I wanted for my installation). And you can get the unit $150 cheaper or so from other sources, but not sure about their stock status at this near-2020 time.

Definitely need Windows 7 or better machine for the install tool.

And you need a 6.5 foot GPS antenna cable or longer per the installation manual, no matter how short the actual length needed. BNC one end, TNC the other. eBay has them pre-made.
 
Last edited:
Agreed with Catmandu - you'll need a Windows machine for the initial setup, and while testing to ensure it is communicating.

I also agree that the 10 ft. cable is fine - no need for a custom harness. Installation was pretty straight forward with the most difficult part of the job being the installation of a test light (optional) and anonymous switch (again optional, and this was easy to do.) I bought some RG400 coaxial cable and the BNC and TNC male/female ends to create my own cable to length. One thing to note is that some have had issues using the stock transponder antenna (AV-11 I think?). I installed a RAMI AV-74 for the 978 mhz frequency and it worked excellently.
 
I did this with the 170 back in summer. I pulled out the old and dying KT76 and put in a used GTX 327 (needed a wiring harness kit, super cheap) and the GDL82. I just ordered the 10 ft cable version. The GDL unit is installed behind interior paneling and the GPS antenna is on the roof. My 170 headliner has a zipper and is easily accessible. I had zero issues programming, on the test flight, or in the 30+ hrs since.
 
catmandu said:
10 ft. should be fine, just make sure the harness has the ANON and Fault wire included, if that's important to you...Definitely need Windows 7 or better machine for the install tool.

And you need a 6.5 foot GPS antenna cable or longer per the installation manual, no matter how short the actual length needed. BNC one end, TNC the other. eBay has them pre-made.
Click to expand...

Thanks! I’m going to keep my installation as simple as possible, hence I don’t see a need for Anonymous Mode or Fault Lights. I’m sure I can dig up a Windows PC.

Any chance you could point me to an appropriate cable on eBay? I did a search but want to be sure I get the right specs.
 
Be advised that the GDL 82 to GPS antenna cable needs male TNC connectors on both ends. I agree that the 10 foot cable is fine. I installed mine in June, and it has been working flawlessly since.
 
GDL 82 on the way from Sportys.

1) A friend ordered one of these for his in-progress GDL 82 install...

49168839013_78ce841fbb.jpg


Before I hit the button, can anyone confirm this is the right fellow? Upthread I think it was stated that one end had to be TNC. And confirm we’re talking about the unit to antenna cable here - I’m assuming that I can use the existing coax from my transponder to the unit as is.

2) Am I to assume no GPS antenna to GDL 82 cable is included with the unit?
 
Last edited:
Sorry, Eddie, I was wrong. Too many installs running around in my head. If you click here, you can clearly see the GPS antenna needs TNC on both ends. And then click here for an eBay cable source I have used quite succesfully in the past (I usually buy cables with at least one end being a 90*, just to have installation options).

I started a conversation with you, if you want to do a phone call, this stuff gets confusing the first time.
 
3 in the green said:
I did this with the 170 back in summer. I pulled out the old and dying KT76 and put in a used GTX 327 (needed a wiring harness kit, super cheap) and the GDL82. I just ordered the 10 ft cable version. The GDL unit is installed behind interior paneling and the GPS antenna is on the roof. My 170 headliner has a zipper and is easily accessible. I had zero issues programming, on the test flight, or in the 30+ hrs since.
Click to expand...
How do you put a GDL82 in a certified plane without using a Garmin approved installer?
 
Stewartb said:
How do you put a GDL82 in a certified plane without using a Garmin approved installer?
Click to expand...
By purchasing it and installing it.
 
LOL, yep. I have a few friends that have done same. Not all Garmin products required a dealer install. I have heard of the older ELTs causing some issues if mounted to close to one of those.
 
The unit arrived yesterday, and I unboxed this morning:

49187094553_bd36cf2e7c_c.jpg


What’s in the bag:

49187117068_a0062f3d28_c.jpg


1) Garmin certainly spared no expense on the packaging! No installation manual or templates or whatever. I already downloaded the installation manual, but that seems kinda chintzy.

2) The blue USB cable is one I found at home.

3) TNC connectors are in fact needed on both ends of the GPS cable.

4) I have a friend in the process of doing the same install in a REMOS. He has friends in an avionics shop that said they’d be happy to do the crimping/wiring harness for us.

May work on physical placement of the unit later today. Will order the two coax cables I need once I’m sure of the lengths required.
 
Have fun, FastEddieB. The job is fairly straight forward, though I personally added a separate circuit breaker for the GDL-82, so I added a little complexity. I bought a long USB cable so I could connect it (and leave it connected) to the GDL-82, and coiled the cable in a map pocket in the cockpit. When there are updates to the GDL-82, I can pull out the cable and update the unit with a laptop sitting on the wing rather than inside the cockpit.
 
1) There is no printed manual. You have to download it. More and more common nowadays.
2) Any old USB cable will work. In my installation I was able to bring the USB connector to an accessible point under the pilot's seat, so I only attach the extension when I need to program.
3) You missed my post last Wednesday if this surprised you.
4) That helps.

Order cables a bit longer than you need. That is better than discovering you didn't account for control cable clearances, or other routing issues. It won't be the same in your airplane, but here are a few pics of my installation:

DSCN5871.jpg

DSCN5872.jpg

DSCN5873.jpg

It is a DA40, that is why you see all of the composite material...
 
Nice photos. I’ll have some on my progress tomorrow.

No, the two TNC ends didn’t “surprise me”, I meant my “in fact” to make clear it was just a confirmation.

Measuring for and ordering cables tomorrow. I’m going to order my GPS cable in two pieces so I can still easily remove my panel.
 
Navair, I like what you did with the bonded studs. I’m just going with the Super-Lok Velcro - I think it’ll be fine.

Added aluminum stock to the mounting brackets to allow for larger Velcro strips:

49194078346_8d6dc92c69_z.jpg


Under-seat location:

49194276667_a039169177_z.jpg


With seat in place, still allowing access to the D-SUB:

49193576818_c167543cf6_z.jpg


About to order the necessary coax cables.

As an aside, does anyone know if the transponder signal will pass through the unit when it’s not powered up?
 
With an Experimental you can be creative. On my aircraft, my A&P/IA won't sign off on something unless it is done by the book (AC 43.13 and the GDL 82 Installation Manual, which states to attach the unit using 4 - 6/32 screws and locking nuts). No way he would approve affixing an electronics box by the wires and velcro. That is why mine is secured by the 2 bonded studs in the photo, plus 2 locking clip nuts on the ground plane strap. Plus, he gave it a few good yanks to make sure it was secure...
 
Last edited:
NavAir said:
No way he would approve affixing an electronics box by the wires and velcro.
Click to expand...

Like you say, being EXPERIMENTAL allows one to experiment.

That said, this “Velcro” is not the garden variety, and I am confident it’s strong enough to hold a 2 lb box.

I showed my install to a friend who has a Cirrus, and your bonded studs, and he made the point that Cirrus uses a fair amount of Velcro in their planes. The antenna for GPS #2 in my Cirrus was Velcro’d to the bottom of the glare shield with the “garden variety” of Velcro. Did not turn out to be the greatest idea since a combination of heat, time and gravity tended to work on the Velcro adhesive, leading to the antenna dropping off, and seriously degrading the #2 GPS sensitivity. Never happened to mine, but was a known issue.

But I do appreciate the feedback - thanks.
 
Last edited:
Yep, there are a lot of ways to skin a cat. It is just that with a Certified AC, the FAA specifies not only how you must skin it, but what kind of knife to use.

You are right about the "super velcro" being strong enough to support a 2 pound box. But remember that your installation is not just for the 1 G situation we fly in 99.999% of the time. The cockpit in my aircraft is certified to protect the occupants in a 26 G forward crash. The GDL 82 would weigh 52 pounds in that circumstance, more than enough to come forward and maybe break your ankle...

The only velcro in the DA40 is used to affix some of the upholstery (and my Zaon MRX velcro'd to the top of the glare shield).

Steve
 
I use velcro for lots of airplane parts, including GDL, Spidertracks, 50% of my interior... Velcro is an awesome tool.
 
I just noticed a note in the installation manual for the GPS antenna:

2.4 Antenna Grounding
The antenna is grounded through the mounting hardware. The mounting hardware (washers and nuts) and doubler plate should make contact with an unpainted surface ensuring proper antenna grounding.

Does this mean that if mounted to composite or other non-metallic surface one needs to run a ground wire to its mounting hardware? Similarly, does the GDL 82 itself require its case to be grounded beyond the ground pin on the multipin connector?
 
FastEddieB: I have a different antenna installation (a Comant CI2680 COM/GPS antenna). But the installation does require a ground plane. In my airplane (composite) the ground plane is provided by metal (copper and aluminum) foil on the dorsal interior of the fuselage. The GPS antenna would probably work without a ground plane, just not as well...

DSCN5857.jpg IMG_2986.jpg
 
Thanks. I can apply similar tape to the underside of my glareshield, if needed. Can I ask your source for that?

And I see you did run ground wires to your antenna base. Is the GDL 82 similarly grounded?
 
Last edited:
The copper foil was from Amazon: https://www.amazon.com/gp/product/B074P754N1/ref=ppx_yo_dt_b_asin_title_o09_s00?ie=UTF8&psc=1

but it shows as not currently available from them. I'm sure an internet search will find something similar.

Just make sure that the foil ground plane is physically connected to the GPS antenna screws (No Velcro! ;)). The grounding wires go to the braided metal shield around the coax cables. This is the method Diamond used for the COM antennas, so I emulated it for the GPS antenna cable as well. Diamond actually went crazy with shielding/grounding: 1) the coax cable, 2) the metal braided shield around the coax cable, 3) the wiring runs in metal conduit in the composite airframe, 4) metal grounding straps, and 5) there is wire mesh imbedded in the exterior composite material.
 
Thanks for that.

I wonder how necessary the “ground plane” really is. I’ve stuck GPS antennas all sorts of places with no ground plane necessary. In my Cirrus, the #2 430 antenna - the one stuck to the bottom of the glareshield with Velcro - had no ground plane apparent and seemed to work and obviously passed FAA muster.

As an aside, my basic installation only utilizes 6 pins of the multi-pin connector:

49204461542_12455b32db_z.jpg


Hopefully getting that wired up tomorrow.

Cables ordered from the eBay source recommenced above. $40 altogether for the 3 I needed. I called a local avionics shop, and they said just one right-angle TNC connector was $25, so it would have been at least $100 for them to do it.
 
I would not worry about a ground plane for the gps antenna. It should work fine . However, I am curious what transponder antenna you are using. Since you are using a GDL82, you need a shark fin type transponder antenna like a RAMI AV74. The standard stick and ball antenna has a vswr suitable for 1090mhz and might be too high at 978mhz. A ground plane becomes more important when installed on a transmitter to insure proper transfer of power to the antenna in order to prevent damage to the power stage of the transmitter.
 
Doug Reid said:
However, I am curious what transponder antenna you are using. Since you are using a GDL82, you need a shark fin type transponder antenna like a RAMI AV74.
Click to expand...

Here’s what it looks like:

49208707787_99741fb564.jpg


I think it may be a Honeywell KA-61. That’s what’s listed in a generic Equipment List for my plane. It’s not on Garmin’s approved list, but I think the general advice was to try it, and if it works, it works.
 
The fellow who suggested that the ground plane is probably not required for the GPS antenna is correct, it will probably work fine without it. The reason I put it in my aircraft it that the Diamond SB to install the Comant COM/GPS antenna called for it. It may be necessary for the COM antenna sharing the radome with the GPS antenna... And I have the same transponder antenna on mine, and it works fine.
 
To answer my own question, I contacted Garmin. If power is lost to the GDL 82, the transponder’s signal will not pass through it - they said it would appear normal on your transponder, but ATC would not see a signal.

I was wondering if I could hook up all the coax and wait for later to do the power, but I guess not.
 
FastEddieB said:
To answer my own question, I contacted Garmin. If power is lost to the GDL 82, the transponder’s signal will not pass through it - they said it would appear normal on your transponder, but ATC would not see a signal.
Click to expand...

That answers a question I had about the GDL-82. I'm thinking of putting it on a separate power switch in order to just have the transponder/encoder signal going out just for those times when I might want to do this for whatever reason. I was assuming the tx/encoder signal would pass through with the 82 turned off, but you've determined from Garmin that it won't. Do you think a simple coax by-pass going around the 82 and tying back into the main cable going to the antenna would work? Would such a thing interfere with normal tx/82 operation when the 82 is turned back on?
 
Well, in my installation I could always just unplug my transponder “out” coax from the unit and plug it back into the antenna directly. Easy peasy, though I don’t anticipate wanting to.

Or, just use a switch like this, maybe combined with a splitter.

49230157938_a518ce3622_z.jpg


Don’t see why switching back and forth would bother the GDL 82 at all.
 
Those are both great ideas. I've been thinking to mount the unit back in the fuselage however, not accessible in flight. Both of your suggestions would require that it be more accessible than I've been thinking.

I'm still curious whether I could just turn it on or off from a panel switch and, if off, have the tx signal just automatically go around the unit with a bypass. The question would be whether the existence of the bypass would affect the operation of the GDL-82. Thanks for taking the time with your suggestions and even posting a picture with source of the splitter switch!

****************************************

For flights outside the country, I think Uavionix's SkyEcho II at about $500 would provide compliance for Canada, Mexico and actually the rest of the planet. The GDL-82 might need to be turned off for the 1090ES transmitter to function. Looks like Canada is going to require ADS-B (or Electronic Conspicuity perhaps a more accurate term) for general aviation below 12,500 in 2022.
 
Doug Reid said:
Since you are using a GDL82, you need a shark fin type transponder antenna like a RAMI AV74. The standard stick and ball antenna has a vswr suitable for 1090mhz and might be too high at 978mhz.
Click to expand...

I used my already installed stick and ball when I put in my GDL-82, no issues getting a good performance report and, eventually, a rebate.
 
The antenna pic you posted of a KA61 is ok, if memory serves me correctly. It meets TSO requirements specified in the GDL82 install manual. A 1090 stick and ball antenna would probably work just fine, but in order to satisfy the install requirements, I usually go with the AV74. The antenna has to be broad banded to match both 1090mhz and 978 mhz . Good luck...I think you will be happy with your decision to go with the GDL82.
 
Baby steps.

Antenna coax and 1/2 of the GPS coax installed just now:

49240147771_2df82f9427.jpg


49240364082_e6f2df8b5d.jpg


Let me say that the coax fabricated by WiFi Experts LLC looks to be of very high quality.

The next and bigger step is pulling the panel to mount the GPS antenna, routing it’s cable and piggybacking onto the transponder breaker and finding a good ground.

To be continued...
 
I’m trying to wrap up the install today, but I just had a recurrence of Mature Onset Dyslexia...

I got the GPS antenna mounted to my glareshield, but it was sitting on my bench “backwards”. It wasn’t until I had all the holes drilled and the antenna mounted that I realized the antenna would end up facing the wrong way:

49278637917_22dd0bccc8_z.jpg


49278435226_85348a27e1_z.jpg


The aerodynamics isn’t a factor of course, but is the backwards mounting an issue otherwise? Rotating it 180° wouldn’t be a huge issue, but would mean relocating the connector hole and would leave two screw holes to be capped. It actually doesn’t look horrible as it is, kinda mimicking the lines of the nose.

Anyway, now just have to run power and ground and program, and I should be done.
 
Not a factor, press on. I actually like it. Given the lines of the Sky Arrow, it kind of fits.

If the white glares off the canopy, a black felt cover will not harm anything.
 
You must log in or register to reply here.
Back
Top