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I'm Mode C-less

LettersFromFlyoverCountry

LettersFromFlyoverCountry

Well Known Member
After obtaining flight following yesterday and establishing radar contact and squawking the appropriate code, the controller told me my Mode C was not operating and asked me what altitude I was at?

"3580," I replied, and that seemed good enough for him.

A few minutes later, he was calling my location out to an inbound twin to St. Paul.

"We've got him on the box, but we don't show an altitude," the pilot reported to him.

"He's at 3500," the controller replied. And that was that.

I'm thumbing through the Garmin 327 manual in search of anything that might provide a clue as to why the altitude is not being received at either one of these locations.

The 327 display does show a pressure altitude reading -- the correct one -- which is coming from the Dynon D100 altitude encoder.

If this is showing correctly, is there anything that I've failed to configure that is preventing Mode C?

The antenna is the cheap rod antenna from B&C. Van's has a $39 rod antenna. I don't know if this is the same antenna or whether it might be a better choice, nor do I know whether the antenna could be a source of the problem.
 
Mel said:
Make sure the mode C is turned on on the Dynon.
Click to expand...

The only data I can find in the D100 manual regarding Mode C is in the autopilot section, which I do not have.

Wouldn't the fact the pressure altitude is being interpreted correctly by the 327 indicate that the D100 is providing whatever it needs to provide?
 
If your 327 displays the correct pressure alt., your Dynon is fine.

Just make sure you were in the Alt mode on the 327.

If that is not the problem, you will need to go see Stein for a xponder test.
 
Not sure about the D100, but my D10A manual shows:
More>Setup>More>AltEnc. You may toggle between 10 and 100 feet increment and select among 4 different output formats.
Format 4 for Garmin GTX327(set on Icarus input), Baud rate 9600.

Looks like if the alt is showing on the Xpnder, it should be OK, but I'm not sure.

Was the mode C working during your Xpnder certification?
 
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Brantel is correct, if you are showing altitude on the 327 then make sure you had the xpdr in "ALT" mode, not "ON". You have to hit the ALT button for it to report mode C.
 
Make sure it's on alt and not standby

I had a similar issue last week, but after some trouble shooting realized I was on standby, it was a slightly humbling call to atc
 
Walt said:
Brantel is correct, if you are showing altitude on the 327 then make sure you had the xpdr in "ALT" mode, not "ON". You have to hit the ALT button for it to report mode C.
Click to expand...

I have it set up with the GPS so it automatically goes to ALT on the takeoff roll.

Kinda kicking myself for not recycling it at the time a problem was first reported, but I was in a pretty busy area and was watching for traffic.
 
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If your signal is low you may have connector issues. When I find low power output a lot of the time the connector at the antenna is not good or the antenna itself does not have a good ground plane.
 
CraigC said:
If your signal is low you may have connector issues. When I find low power output a lot of the time the connector at the antenna is not good or the antenna itself does not have a good ground plane.
Click to expand...

This is exactly what I was going to suggest. First two things I would do :

1) Replace the cable between the transponder and the antenna. This could even be a temporary thing - the point is to eliminate the existing cable as a source of problems.

2) Swap out the antenna. This is pretty easy to do as well, especially with the rod ones. We might have a unit in our hangar you could swap to try.

-Brad
 
I'll go ahead and rewire the antenna and see what bappens. The plane is going to be down for a few weeks of leg fairing and intersection fairing installation work anyway.
.
 
Garmin 327 woes

I have been having problems with my 327 since April (2012). It does not work...no return seen by ATC. I replaced all the cable and put a new antanae. Swapping other units (320 and 327) into the tray and flying shows no problems at all with the wiring, antenae etc. (problem is in the box)
A local bench test for $80 (said it was fine)....then sent to Garmin for $700 (its been back twice) and it STILL does not work.....I am not sure what they are doing as they tell the local Avionics shop nothing about what their repair facility has done....this is getting very frustrating.

unit is 3 years old.....!
Has anyone else had these problems with Garmin ? Any contacts that could help me would be appreciated. (I live in Canada)

signed
Frustrated
 
Marc DeGirolamo said:
Any contacts that could help me would be appreciated. (I live in Canada)
Click to expand...


You might try contacting "G3expert" here on the forums. It is an address used by a number of guys at Garmin who are homebuilders and really reaching out to the experimental community. Don't know if they can help you - but I bet they will listen...
 
I've had my 327 overhauled for the flat fee after I fried it monkeying with a bad encoder. After the overhaul it has been ROCK solid!

I don't think you need a complete overhaul though. Although I am a bit puzzled. If you see an altitude on the 327 then that proves you are getting data from your encoder (dynon), if ATC sees you then that proves your antenna set up is working (at least partially). The only remaining component is the 327. So..:confused:


I HAVE seen certain areas where it is the ATC equipment with the sub par performance. I say try a different ATC facility and/or a different geographic area. It may not be YOUR problem after all.
 
Garmin 327

I had a problem awhile back where mine was intermitant. Saw a post where someone else was having a similar problem, Stien suggest he replace the 90 degree solder connector with a straight out BNC connector.
I talked to Stien and he suggested I order a new backplate with the BNC connector. After replacement I have had zero problems. Might check to see if you also have the 90 degree connector. Hope this helps
 
rv9av8tr said:
Oh for Gods sakes... $700... that's NUTS. I really do try to boycott Garmin products for these kinds of practices.... arrrgggg.....
Click to expand...
Garmin charges a flat fee for avionics service. That was the price for the 327 service - didn't matter whether it needed a new board and PA or just a reflash. YMMV.

TODR
 
Marc DeGirolamo said:
I have been having problems with my 327 since April (2012). It does not work...no return seen by ATC. I replaced all the cable and put a new antanae. Swapping other units (320 and 327) into the tray and flying shows no problems at all with the wiring, antenae etc. (problem is in the box)
A local bench test for $80 (said it was fine)....then sent to Garmin for $700 (its been back twice) and it STILL does not work.....I am not sure what they are doing as they tell the local Avionics shop nothing about what their repair facility has done....this is getting very frustrating.

unit is 3 years old.....!
Has anyone else had these problems with Garmin ? Any contacts that could help me would be appreciated. (I live in Canada)

signed
Frustrated
Click to expand...

Might I suggest you find another avionics shop... A "bench check" is about a 15min affair that many shops do for $50 or less....they charged you for what usually is an hour+ of work. Also, the flat overhaul cost on a 327 is $575(it's published publically on their website) so if they charged you $700, then you got suckered. Also, after the first overhaul, there is a new warranty on the repairs, so you shouldn't be paying again. If you bought it new from a reputable dealer you shouldn't have any of these issues at all (good dealers WILL take care of you).

Also, to be blunt, Trying to "boycott" products based on inaccurate information or poor experiences others have with less than stellar dealers is just stupid IMHO. This is why forums sometimes are a difficult place to sort wheat from chaff. In this case, someone posted what they paid for something (not the CORRECT price) and others have jumped on board and accepted it as a factual bit of data - yet it isn't correct as to what the guy should have paid.

I don't know the age of Bob's unit here tonight, but it's likely we'll get it taken care of. Threads like these are tough when they take place on the weekend and end up in the internet BEFORE anyone calls the dealer or mfgr to see if there is a simple fix (or a few minutes with a tech to find the problem)....As in Geralds case, an updated backplate/connector on an OLD box was a reasoable solution.

Cheers,
Stein
 
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Let me attempt to translate what Stein said above:

"Call Stein with your complaints BEFORE venting on VAF, or on the web." ;)

Then you can add yet another post about how great a guy Stein is............:cool:
 
tkatc said:
I HAVE seen certain areas where it is the ATC equipment with the sub par performance. I say try a different ATC facility and/or a different geographic area. It may not be YOUR problem after all.
Click to expand...

It was that inbound plane that also couldn't see my altitude on its 'box' while seeing my existence that leads me to believe the problem is with me.
 
PCHunt said:
Let me attempt to translate what Stein said above:

"Call Stein with your complaints BEFORE venting on VAF, or on the web." ;)

Then you can add yet another post about how great a guy Stein is............:cool:
Click to expand...

I hope everyone remembers this advice the next time the post is about the media instead of a piece of avionics.

I'm not sure who you're referring that to but you'll notice that the original post contained legitimate questions based on the possibility that I'm missing something in this particular situation -- a configuration setting, for example -- posting it on Van's Air Force is more than a legitimate and appropriate use of the medium.

I'm not responsible for what other people post in the subsequent thread, which is the first double-hijacking of a thread I think I've seen on VAF.

When you guys are done debating the role of social media in airplane building, maybe you can get back to my original questions.
 
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LettersFromFlyoverCountry said:
It was that inbound plane that also couldn't see my altitude on its 'box' while seeing my existence that leads me to believe the problem is with me.
Click to expand...

Not sure what equipment you have, or the other aircraft, but if the ATC ground station has an issue (like not seeing your altitude because IT has problems) then in theory, the ground station would not broadcast your altitude into the data stream.
 
tkatc said:
Not sure what equipment you have, or the other aircraft, but if the ATC ground station has an issue (like not seeing your altitude because IT has problems) then in theory, the ground station would not broadcast your altitude into the data stream.
Click to expand...

Ah, so his "box" (presumably some sort of TCAS) would be getting a stream from ATC as opposed to monitoring an interrogation reply from my 327?

Here's a question for you. Do you ever see a situation where you see the target's transponder but not altitude but then you get Mode C with a higher altitude?
 
The "Box" usually means TCAS, TCAS operates independently from ATC ground stations. TCAS scans the area and interogates transponders very similar to the way a ground station does.
 
LettersFromFlyoverCountry said:
Ah, so his "box" (presumably some sort of TCAS) would be getting a stream from ATC as opposed to monitoring an interrogation reply from my 327?

Here's a question for you. Do you ever see a situation where you see the target's transponder but not altitude but then you get Mode C with a higher altitude?
Click to expand...

Don't take my perception of ADS-B as gospel. It is new to me and I am still learning but my above statements reflect my current understanding.

As far as higher altitudes and mode C....YES! I have been bitching about certain areas of my radar coverage being "weak" or error prone to the technicians for the last year or so. My RADAR return is fine, but the interrogator portion (the part that reads the transponder) has problems. They cite geographic anomalies for most of the problem but I am not sold 100%. My neighboring facility can see the altitude without a problem on many of the targets I do not get a mode C reading on. This is why I suggest checking with another ATC facility (or geographical area) to see if you experience the same issue.
 
Ohhhh...just realized you may be referring to TCAS and not ADS-B. in that case, if ATC isn't getting mode C, and neither is the TCAS equipped aircraft in your vicinity, then I'd say the problem was yours alone.
 
Bob,

Quit looking on the dark side! Think of it this way, you are just one step away from having your own stealth aircraft. How cool is that;)

Bob
 
Less

Take a big dose of Milk Of Magnesia, Bob. That will cure anything!:D

Seriously, bet it's just a setting or a loose connector.
 
LettersFromFlyoverCountry said:
I'm also less than a step away from having an unflyable aircraft since I operate within the Mode C veil of MSP.
Click to expand...

Yep, we violated about ZERO non-mode C aircraft in the past 20 years!! The intent of the rule is for you to be seen by ATC and other TCAS traffic since a mode C veil has a concentration of traffic (usually surrounding class B airspace). You are honestly WORKING the problem so even if LIGHTENING were to strike, and they came after you, you would have a valid argument.

I am curious to know what the fix is to this issue so please keep us posted.
 
LettersFromFlyoverCountry said:
Flew down to Rushford on Saturday -- greatest little airport ever -- and neither Minneapolis Departure nor Minneapolis Center had a problem receiving my Mode C. The only change I've made is manually cycling it to ALT as part of my runup.
Click to expand...

Glad it is working. I had this issue a couple times where I had to cycle it to ALT based on controller feedback of not seeing my alt., but only once or twice. Has worked just fine now for some time so you might find it does not need any more cycling. I am not sure if there is a start-up protocal setting or if the 327 starts up in the last state left, or what.... I just have not had the need to get to know it that well.
 
TCAS sends its own interrogator signal. So it would seem that his equipment is the issue.


If the radar is based on the field you can always try asking the (not busy) tower to set their filters below field elevation and (after turning your xponder alt encoding to manual, not slaved to GPS) turn your transponder on and see if they're getting a hit.

i would call them on the phone prior to doing this. some guys won't know wtf you're talking about. or you could just fly around the pattern and ask if they're getting a hit (probably the best option).
 
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Issues with ALT solved with some electrical contact cleaner

I had some issues early on with my transponder mode C. After a few shots of electrical contact cleaner in the connector behind the 327, I was fine. Didn't work the first couple times, but the third time worked good. Maybe some crud from the build. Perfect the last 6 years!
 
It's more likely that the unit was not seated all the way than dirty connectors. There is very little engagement of these pins, proper engagement is critical to proper operation.

This is the reason that any time the aircraft connections to a transponder have been removed and reconnected, each altitude reporting code line (in the case of the newer aircraft, the digital data bus) must be tested for integrity of connection.
 
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