Garmin 750XI Com Issues

[jetdriven]

4 hours ago, Marauder said:

The old wire did not have any conduits that were used. The wire was either tie wrapped or attached to the roll cage with metal clips. When it went through a bulkhead, there was a rubber grommet.

I refreshed the grommets, and when there were questionable areas to transverse, I would wrap the wire in a plastic spiral wrap. You can get the spiral wrap at Aircraft Spruce.

Like what I used for the CiES wiring:


BTW - I almost lost an arm putting in the new blue grommet!


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Where do you get those clips at?

[Marauder]

Where do you get those clips at?

You talking about the blue one?

https://www.aircraftspruce.com/catalog/eppages/ms21919wcj.php


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[Marauder]

Where do you get those clips at?

Or if you are talking about the clip that the Adell is screwed to, it was there from the factory. I replaced the black Adell with the blue one.


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[Speed Merchant]

On 7/12/2022 at 8:41 AM, Marauder said:

SWR tests determine the health of the wiring and connectors. That’s the issue with some of these shops. They don’t take the time to check out the wiring. Putting new with old isn’t always a good idea. Especially when they don’t see stuff like this:




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They just replaced the coax-I pick it up Monday. Hopefully I will be happy. Thanks

[Speed Merchant]

On 7/12/2022 at 8:41 AM, Marauder said:

SWR tests determine the health of the wiring and connectors. That’s the issue with some of these shops. They don’t take the time to check out the wiring. Putting new with old isn’t always a good idea. Especially when they don’t see stuff like this:




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thanks for the picture

 

[Speed Merchant]

On 7/12/2022 at 10:48 AM, Marauder said:

I can’t find the receipt for the amount I bought. The math isn’t too hard. You will need to know where your VOR splitter is. The distances you need to measure are:

1) Distance from the VOR antenna to the splitter (that will be one wire).
2) Distance from the splitter to the Nav radios. My splitter was in the avionics bay and we moved it under the panel.
3) Distance to the Com 1 radio’s antenna.
4) Distance to the Com 2 radio’s antenna.
5) A fudge factor.

If you have the time to take the plane down, I would pull the interior and see where the wires run. Then measure the lengths. My top com antenna was routed through the pilot’s side. I re-routed to the co-pilot’s side, under the door. My pilot’s side is filled with wiring for the Aspens, the Lynx and who knows what else.



The co-pilot’s side was much easier to work with.



My belly antenna was routed up through the left side.

If you take on the project, it is also a good time to check on the condition of the antenna groundings and the general health of everything behind the panels. I spent a lot of time correcting poor routing and storage of wiring from avionics shops.

If you look at this picture, you can see the Aspen’s wiring was literally just piled in behind the panel. It was a rat’s nest. I cleaned it up and made sure everything had a stand-off to prevent rubbing and chafing chances (first picture).



I’ve owned my plane for 31 years. My philosophy has always been to be proactive on updating and upgrading things over time. I don’t want to be flying over some crappy weather to find out that I should have probably done some preventative maintenance. A side benefit of being proactive, the plane is ready when you need it.

It’s not to say things will fail (like my famous alternator failure of 2019), but the likelihood is a lot less if you are staying ahead of the storm.


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thanks for your post!

[Speed Merchant]

On 7/12/2022 at 11:21 AM, PT20J said:

Garmin's release notes are pretty cryptic. There is a note from a service bulletin in 2013 that says:

COM Software Version 2.12 contains the following changes from Version 2.11:

• COM Software Version 2.12 provides improved squelch control over Version 2.11. It is helpful only in those installations that experience open squelch (receiver too sensitive) after utilizing the COM Monitor Mode.

This may be the change the increased the default squelch setting. 

If you have a second com with good reception, you can climb to  3-5000 feet and establish communications with a distant facility on the good radio. Then try the GTN, and if you cannot hear a reply, transmit on the GTN but listen on the good radio. If you get a response, you know that the GTN transmitter is good and you can try adjusting the squelch.

Skip

Thanks!

[FlyingScot]

 

FYI - Garmin recently released a software update for the 650 and 750 Xi to permit a wider range of (read negative) squelch threshold values (as accessible in Setup).

Since upgrading to the Xi units from the earlier version (several years ago), I have had trouble with the squelch breaking a low reception signal levels - often I ended up flying with the squelch disabled to ensure I would not miss center. I have both a 650Xi and a 750Xi installed and they exhibited the same behavior.

Salvation is at Hand! There is now a software fix for this (as of last month) and it worked for me.  

https://support.garmin.com/en-US/?faq=Zm4qxZqwIG00gPwgNhgDW8

Updated GTN XI main software to Software Version 20.42:

• Increased the range of the COM Carrier Squelch setting in Configuration Mode to resolve weak COM reception issues experienced in some installations (Requires COM Software Version 2.11)

NOTE
Negative COM carrier squelch settings require Main Software Version 20.42 and later and COM Software Version 2.11 and later. The COM carrier squelch setting must be set between 0 and 100 before installing older software versions.

https://atlaske-content.garmin.com/filestorage//email/outbound/attachments/24045A_ASDN_Time1716998196333.pdf

Cheers - Bob

 

[Pinecone]

 

 

[FlyingScot]

Missed the thread - thanks! Good News all around. 

[Marc_B]

I've been following this on B.T. as well.  Gonna update the software this week and see how that improves things.  I always thought my legacy GTN had better reception than my GTN Xi...I previously went from 57dB down to 5dB.  But I noticed that sometimes Center could hear me, but I couldn't hear them unless I broke squelch.  Supposedly the radio on the Xi is actually better than the legacy once it's working properly.  As mentioned, a few folks on BT used Carrier Squelch (-25) and Rx Squelch 0.

Probably makes sense to update any pertinent old threads (such as this) in case someone is searching for an answer and just stumbles on an old thread.  Seems like this is a pretty significant impact I'd say.

[jetdriven]

we replaced the legacy GTN 750 with an Xi version two years ago and the com radio has about half or a third of the power that the one that came out of it has. We turn the squelch for basic amd advanced down zero but still even if you open the squelch, it sounds like it’s 50 miles further away than it really is. finally they took it back and it’s at Garmin. They’re doing something to it, and we have a loaner 750 which again, performs great. We also bought a GNC 215 and that thing works pretty good too. 

[M20F]

On 7/12/2022 at 8:41 AM, Marauder said:

SWR tests determine the health of the wiring and connectors. That’s the issue with some of these shops. They don’t take the time to check out the wiring. Putting new with old isn’t always a good idea. Especially when they don’t see stuff like this:




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Why would anyone want to see that knee!

[wombat]

I think there is a problem like that wire on my GTN-750Xi    When I transmit while the engine at low RPM the whole engine monitor freaks out (temps show values beyond reasonable limits - CHTs of 8k degrees for 1/2 second then back to normal)

And ATC says I'm kind of hard to hear sometimes, and I don't receive all that well either.   This is after trying two separate GTN 750's in the same tray.

[Pinecone]

@jetdriven had an issue with his 750Xi transmit.  After a thorough check out at the avionics shop, it is back at Garmin for warranty service.

The two threads (here and in Avionics) are bout receive issues.  A LOT of people have had Rx issues.

[Marauder]

Why would anyone want to see that knee!

Obviously you! Here is a better shot. 7 years older but still looking pretty good.



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[Marauder]

I think there is a problem like that wire on my GTN-750Xi    When I transmit while the engine at low RPM the whole engine monitor freaks out (temps show values beyond reasonable limits - CHTs of 8k degrees for 1/2 second then back to normal)
And ATC says I'm kind of hard to hear sometimes, and I don't receive all that well either.   This is after trying two separate GTN 750's in the same tray.

I had a similar issue. It was smeared in that timeframe when Garmin was dealing with open squelch issues that the short term fix was adjusting the squelch and losing some transmission range.

After that was resolved, I was still having transmit issues. I replaced all of the RG-58 with RG-400. Someone more familiar with the installation requirements of the Garmin stuff can comment whether that is a requirement or not. I think there is a lot more RG-58 still being used on new installations. Replacing the cabling fixed the transmission problem (never had a noise issue).

Another thing to check is the antenna. I had a GNC 355 installed recently and was having issues with transmissions being heard. The problem was masked because the radio that was removed was a 16W GNC255B. Turned out to be the 7 year antenna that was bad.


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[jetdriven]

In this case, it seems pretty clear cut, the radio that came out was a 750 and it worked great, this xi is terrible, and the one that’s in there for a loaner is a 750 and it works great too.

[Shadrach]

 

On 7/12/2022 at 10:05 AM, Fly Boomer said:

Is RG-400 expensive?  I'm tempted to replace all my coax "just because".

 

On 7/12/2022 at 10:07 AM, Marauder said:

$3.30 per foot at today’s price. I’ll look to see how many feet I bought. I replaced both coms and Nav wiring all the way back to the tail.


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Spruce wants $5.50 per foot. You can do better at Field Components they are cheaper and often ship same day. 

Currently $2.89 per foot

[EricJ]

RG-400 is less than $1.50/ft from various suppliers on Amazon.   It's cable, I've been getting it there for many years with no issues.  I've been doing radio comm research for a living for >35 years; it's fine.   

https://www.amazon.com/gp/product/B07WJG7XF6

 

[Fly Boomer]

2 minutes ago, EricJ said:

RG-400 is less than $1.50/ft from various suppliers on Amazon.   It's cable, I've been getting it there for many years with no issues.  I've been doing radio comm research for a living for >35 years; it's fine.   

https://www.amazon.com/gp/product/B07WJG7XF6

 

I wonder why RG-400 is so dominant in the world of GA?  I think there are other cables that have similar specs.

[EricJ]

Just now, Fly Boomer said:

I wonder why RG-400 is so dominant in the world of GA?  I think there are other cables that have similar specs.

RG-400 is kind of the standard best-bang-for-the-buck go-to cable for good performance for anything C-band (~5GHz) or less, and it'll go about double that in a pinch.   It is less lossy than older cable types (e.g., RG-58) and just generally much better cable.    You can go cheaper, but it'll cost you something.    If you're replacing RG-58/59 with RG-400, you can expect better performance and happier radios, maybe not so much that you notice immediately, depending, but it will be better.

RG-400 holds up better, is stronger (so less likely to distort due to sag), etc., etc.

It's not just dominant in GA, it's kind of the standard cable for anything <~5GHz where there isn't extreme price pressure or some other niche requirement.

[M20F]

On 6/14/2024 at 12:41 PM, Marauder said:

Obviously you! Here is a better shot. 7 years older but still looking pretty good.



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