GTN 750 650 Squelch & Fuel flow

[Mooney_Allegro]

Rocket Aviator,

From what I was told by Sarasota Avionics, the GTN 650/750 series is a unit designed from the GNS-480, that was an Apollo CX80. Apparently Garmin AT, bought Apollo which is a different division of Garmin, based in Salem, OR. I was told that the coms on the GTN-650-750 work completely different from the GNS530/430, that I had previously. I hope I made sense, because it's a little confusing.

We need to get to the bottom of these safety issues. I believe it's a Garmin issue, since 2 Garmin avionics shops advised me these issues are only happening on the newer units. Lacee, I met you at Homecoming! I spoke to you briefly concerning this. Don't know if you remember me. I'll let you know the resolution, if any when I get these new radios. Dave

[MB65E]

Similar issue to comment on...

Same story, squelch turned all the way up etc... On the GTN635 (650-no nav) I installed in an composite aerobatic airplane with no audio panel.

Knowing that it was composite airplane with minimal ground planes, I opted for the 16W updated power output. Anyway, receiving was always horrible for the last year since the install! New antenna, coax, ground plane mesh wire etc... Still on change. Finally, after several discussions with Tim at Western Avionics, I decided to remove the headset ANR power adaptor. This was a little power jack that my helmet plugs into. Low and behold, on my flight this week I could receive and transmit with no issues! If your ANR is on a CB, try pulling that. For kicks, I'd be interested to see if there is a correlation between the squelch and the power for the ANR.

-Matt

[Piloto]

Some receiver squelch designs are more sensitive to RF noise than others. Amplitude squelch design will open when a signal or noise is present. Coherent squelch design only opens when a carrier signal is present but not to noise.

 

If the squelch does not open with the engine off but when is on and in-flight I would suspect and onboard source of noise. This could be the alternator/generator, magnetos, or other electrical devices. Try turning off each device to see if the noise goes away. Also try power off your cell phone.

 

José 

[Mooney_Allegro]

Another note of interest. My squelches both open up fully & continuously after I turn on the battery switch & avionics switch "in the hangar". When I pull the plane out of the hangar the squelches close & no squelch noise. I called Garmin about this a few months ago, and they told me it's normal for that to happen, that it's the hangar structure that's interfering with the coms. MB65E, I don't have an ANR power adapter, they are just battery powered, but I'll diagnose with turning items off to see any effect. My GTN-650 breaks squelch right after liftoff for up to 45 seconds! It's crazy.

[Piloto]

Some COM receivers are sensitive to nearby FM broadcast stations and that is why somtetimes the squelch will open when in their vicinity. As far as squelch opening in the hangar, is because there is something in the hangar generating RF noise, such as a fluorescent lamp. Looks to me that the squelch setting is set too sensitive.  

 

José

[flyboy0681]

Some COM receivers are sensitive to nearby FM broadcast stations and that is why somtetimes the squelch will open when in their vicinity. As far as squelch opening in the hangar, is because there is something in the hangar generating RF noise, such as a fluorescent lamp. Looks to me that the squelch setting is set too sensitive.  

 

José

 

True to this point, when I fly to Tuscaloosa, Alabama, there is a point where I start tuning in to listen to the ATIS but instead get an FM station.

[Piloto]

True to this point, when I fly to Tuscaloosa, Alabama, there is a point where I start tuning in to listen to the ATIS but instead get an FM station.

 

True to this point, when I fly to Tuscaloosa, Alabama, there is a point where I start tuning in to listen to the ATIS but instead get an FM station.

 

I was refering to the old NAV/COM radios. You should not have this problem on the COM side of the GTN 750.

The FM interference problem on ILS was first brought by the CAA in the mid 90s due to ILS interference from FM stations on the high end of the band.

Details at http://www.caa.gov.qa/sites/default/files/AWN%2004%20-%20Improved%20FM%20Broadcast%20Interference%20Immunity%20standar.pdf

 

ILS receivers are required to have a sharp edge high pass filters at the antenna input to filter out the FM broadcast signals. In the US the FCC and the FAA coordinates the frequency assignments and FM tower location to avoid this problem. The problem shows as swinging LOC deviations and music on the NAV receiver audio.

 

José

[flyboy0681]

I was refering to the old NAV/COM radios. You should not have this problem on the COM side of the GTN 750.

The FM interference problem on ILS was first brought by the CAA in the mid 90s due to ILS interference from FM stations on the high end of the band.

Details at http://www.caa.gov.qa/sites/default/files/AWN%2004%20-%20Improved%20FM%20Broadcast%20Interference%20Immunity%20standar.pdf

 

ILS receivers are required to have a sharp edge high pass filters at the antenna input to filter out the FM broadcast signals. In the US the FCC and the FAA coordinates the frequency assignments and FM tower location to avoid this problem. The problem shows as swinging LOC deviations and music on the NAV receiver audio.

 

José

 

 

 True that, I always use COM2 (KX 165) to pick up ATIS.

[Piloto]

 True that, I always use COM2 (KX 165) to pick up ATIS.

 

Try setting the GTN-750 to 8.33Khz channeling instead of the 25Khz spacing. This may improve the FM inmunity by narrowing the IF bandpass filter. Garmin may have passed the FM inmunity test at 8.33KHz but did not test at 25KHz. No surprise after all this was an European problem and they use 8.33KHz channeling.

 

José  

[Marauder]

Ok, some additional information. I spoke to a shop today that provided some additional observations on the squelch & range problems with the GTN series. The shop told me that some installers are encountering electronic noise from things like the mag that are opening up the squelch. And instead of informing the customer that they have an electronic noise issue, they are turning down the sensitivity of the unit.

This makes sense in my case since I do not have a squelch issue but I have better range on my 20 year old Narco. Does this sound plausible to you guys?

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[Marauder]

Another note of interest. My squelches both open up fully & continuously after I turn on the battery switch & avionics switch "in the hangar". When I pull the plane out of the hangar the squelches close & no squelch noise. I called Garmin about this a few months ago, and they told me it's normal for that to happen, that it's the hangar structure that's interfering with the coms. MB65E, I don't have an ANR power adapter, they are just battery powered, but I'll diagnose with turning items off to see any effect. My GTN-650 breaks squelch right after liftoff for up to 45 seconds! It's crazy.

I have a handheld Vertex radio that will do this in the large hangar at my airport. When I walk into the building, the squelch breaks and stops when I leave.

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[Mooney_Allegro]

Ok, some additional information. I spoke to a shop today that provided some additional observations on the squelch & range problems with the GTN series. The shop told me that some installers are encountering electronic noise from things like the mag that are opening up the squelch. And instead of informing the customer that they have an electronic noise issue, they are turning down the sensitivity of the unit.This makes sense in my case since I do not have a squelch issue but I have better range on my 20 year old Narco. Does this sound plausible to you guys?Sent from my iPad using Tapatalk

Marauder,

It certainly sounds possible, however I never had any squelch or range issues with the 430W & 530W. I know those radios were a completely different design & platform vs the GTN's. Sarasota Avionics notified me that Garmin will replace both of my GTN's, so I should have more information in a few weeks when they make the swap.

[Marauder]

Marauder,

It certainly sounds possible, however I never had any squelch or range issues with the 430W & 530W. I know those radios were a completely different design & platform vs the GTN's. Sarasota Avionics notified me that Garmin will replace both of my GTN's, so I should have more information in a few weeks when they make the swap.

Thanks! Please keep me posted on your progress. I have an appointment on the 20th to have them look at mine.

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[M20JFlyer]

I have been following this thread for two years:

I ALSO have a Garmin GTN 750 with unreliable comm in my J model MOONEY --installed by a certified Garmin dealer.

I have transcripts from HOUSTON, Kansas City, Minneapolis, Atlanta, Orlando, Boston , New York , Chicago ,fort worth, Denver ....

Each of the ATC center(s) I have listed have asked if I can switch radio's WITH A BROKEN UNREADABLE transmission

In addition the Fort-worth/DFW HAS provided a copy of my sportys SP 400 hand held and 23 y/o KX155 compared to the GTN750.

I am really a nice person, AND I have been treated respectfully by Garmin at OSH AND SnF.

All I have ever asked is : GARMIN --PLEASE -- select a dealer of garmins's choice to remove my unit, determine if an antenna or some deficiency exists from the install of my existing GTN750 by the certified Garmin installer and install a new GTN750 WITH THE CURRENT updates...using my unit as a test unit to rectify the anomalies under the auspices of your technicians

Considering the repeated similar anomalies of other GTN 750 units am I being unreasonable??

I need my airplane to GO PLACES, and I need the GPS FUNCTIONS OF THE 750 to be able to travel IMC.

GARMIN: please do not request I remove it and send it to the west coast to be ""looked at"

""I need my airplane to GO PLACES, and I need the GPS FUNCTIONS OF THE 750 to be able to travel IMC "

IS ANYONE READING THIS ( with a unfriendly GTN750 ) PLAN TO ATTEND OSH 2014

If possible, please email me at plyons820@yahoo.com or call 832.655.4203

I am trying to raise an appt with Garmin tech at AIR-VENTURE 2014. Any response

appreciated

Pat

[Marauder]

Pat -- I'm in the middle of this with a 650. Most of my issues have been, like yours, an unreadable radio. My range is also very short compared to my Narco Mark 12D+. My problems have been on various frequencies including 119.75, 126.45 and 126.825. I also think I had an issue with a 13x range. I will be over at an avionics shop and will have another discussion with them on it. This shop is not the same one that installed it.

Most of the current firmware updates have been related to the open squelch issue and nothing through the current 5 rev addresses either a range or clarity problem on the comm. I also have the screen glitch thing going on. It is an intermittent screen flicker. This has not been addressed with the current firmware either.

If my issue doesn't get resolved tomorrow. Keep me in mind when you are at Oshkosh.

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[flyboy0681]

I'm so surprised to hear all of these issues. I don't have a single complaint about my 750 and when I flew over a couple hundred miles over open water last week I heard every word from the Center and they received my replies.

[M20JFlyer]

Marauder,

Thanks for your response, please keep me on your list of those very interested in what you learn. If you get to OSH this year let's meet-up at the MOONEY booth.

Garmin has nothing to gain from disregarding airplanes in the system with less than audible radio 's.

The liabilities of prior experiences in the ARTC system should one of these radio's cause an incursion on a runway or elsewhere is unimaginable.

I have confidence Garmin will be responsible and respond with appropriate attention to the affected GTN radio's.

Again, anyone planning to attend AV-2014 please consider the advantage of meeting Garmin in numbers.

Those of YOU on MOONEYSPACE with the ability to share my above post with Beech, Cessna, Piper or any applicable aviation forums please let this message be my assertive permission to share my comment(s)and concern of the GTN COMM anomalies .

Thanking you all in advance,

Pat. Plyons820@yahoo.com. 832.655.4203

[PTK]

...Considering the repeated similar anomalies of other GTN 750 units am I being unreasonable??...t

Since you asked may I respectfully submit if you're point blank requesting a new unit, yes, you're being unreasonable. Please correct me if I'm misunderstanding you.

Garmin has not asked you to remove the unit and ship it anywhere. They have procedures in place that address warranty, installation, etc etc issues.

As Garmin probably has already told you you need to take it to "a Garmin dealer" of your choosing. They will deal directly with and will be instructed by Garmin as to the appropriate course of action. Garmin is not out to get you but they have their procedures.

I also have a GTN 750 along with GMA35 and GTX33 and couln't be happier! Looking to also install a 650 and GDL88 soon.

[Marauder]

I'm so surprised to hear all of these issues. I don't have a single complaint about my 750 and when I flew over a couple hundred miles over open water last week I heard every word from the Center and they received my replies.

The problem seems isolated to a group of radios. The earliest radios seem to be fine as does the current gen. Mine was made in 2012. I haven't ruled out an installation issue yet either.

That said, there are radios that have been replaced under warranty.

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[jlunseth]

Boy does this sound familiar.  I had a 430AW installed several years ago.  The "A" part is an upgrade to a 16W transmitter and cost, as I recall, about $3500 more than the standard 430W.  To say it has been a disappointment is mild.  I lose communication on the radio with ATC on virtually every long distance, high altitude IFR flight.  It is worse when there are storms in the vicinity, I suppose if they are between me and the ground station they weaken the signal.  I am simply used to it, I "radio check" often if I am not hearing ATC talk to others, and I use my 35 year old King to reestablish contact.  I had my A&P check the installation several times. At one point we swapped units for a different issue, since cured, but the new unit and old unit had the same poor reception. The radio went back to Garmin and was adjusted on their bench a few years ago, it was somewhat better but still not good.  I had my avionics shop adjust the squelch so it breaks at a lower level.  That is unfortunately not a very good solution, because there are many times when I get switched to a new frequency and get constant static, as if there were an open mike on the frequency.  It usually happens with frequencies that start with 125. something.  Garmin has been less than helpful, I even was at the factory for a seminar a few years ago and asked about it.  There was another Mooney owner there, same unit same problem and he was asking.  We were told to go back to the installer. 

 

This is a major disappointment to hear that the problem exists in the 750/650 series.  I was thinking about going to a 750 to replace my old MX20 and would take the old King radio out, but it does not sound like that is an option.  The GPS is great, the radio not so much.

[Marauder]

Well, here is what I was welcomed by my Garmin ON THE WAY to the avionics shop this morning. I am so thankful this happened in visual conditions, although with low vis due to haze. The GPS dropped and returned 3 times in 5 miles. Truly sad when you need to rely on a defunct company's radio over the high priced box. The only good news is that I am at the avionics shop... Sent from my iPad using Tapatalk

[ArtVandelay]

Well, here is what I was welcomed by my Garmin ON THE WAY to the avionics shop this morning. I am so thankful this happened in visual conditions, although with low vis due to haze. The GPS dropped and returned 3 times in 5 miles.

Did you do the RAIM prediction?

 

My avionics shop replaced all my coax cabling (comm and gps), said it was required by Garmin, I wonder if this is a a new requirement in order to address these issues?

[Marauder]

Did you do the RAIM prediction?

My avionics shop replaced all my coax cabling (comm and gps), said it was required by Garmin, I wonder if this is a a new requirement in order to address these issues?

Tried to but the RAIM prediction site uses Java that won't work on my iPad. The ironic part is I had one other of these failures not long after I bought it. I was shooting the ILS to the same runway at the same airport when the GPS went LOI. This time I was using the LPV approach to the same runway. Wonder if there is something in this environment.

Speaking with the avionics guys they said they haven't heard of drop-outs in the area.

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[ArtVandelay]

Tried to but the RAIM prediction site uses Java that won't work on my iPad. The ironic part is I had one other of these failures not long after I bought it. I was shooting the ILS to the same runway at the same airport when the GPS went LOI. This time I was using the LPV approach to the same runway. Wonder if there is something in this environment.

 

I'm talking about using the GTN-650 RAIM prediction page, see pg 14-10 in pilots guide.  No Java or IPAD required. When I did my instrument training, I did this every time.

[Marauder]

I'm talking about using the GTN-650 RAIM prediction page, see pg 14-10 in pilots guide. No Java or IPAD required. When I did my instrument training, I did this every time.

Sorry, I thought you were talking about the FAA site. The one in the GPS showed nothing.

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