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  #11  
Old 05-22-2022, 12:54 PM
Dandlac58's Avatar
Dandlac58 Dandlac58 is offline
 
Join Date: Oct 2021
Location: Sierra Vista
Posts: 44
Default The Plot Thickens...

Quote:
Originally Posted by TruTrakAndrew View Post
Yes, you can engage the entire system on the ground and do not need to be moving.
Hi Andrew and Bob,

I think I may have found the culprit. Long story so you get all the facts:
I climbed into "Super Tweety" my RV7A this morning, went through my normal checklists. Started the engine, turned on all of the avionics including the GNS430W, The TT A/P, the SL40 (COM2), GTX327, EFIS, EIS, Uavionix Echo. Programmed a short flight from KFHU to TOMBS Intersection to E95 into the 430W and activated it checking to make sure it transferred to the EFIS. It did. The 430W also attained 3D Differential Navigation with several satellites. Taxied to the runway, did my runup and mag/prop checks. Departed and with a right turn out, I turned to my initial course of 022 degrees. As I was climbing, I pushed the center knob on the TT to activate it, then pressed the Mode button to have it track the course via GPSS. It did. As I reached my cruise altitude of 6500' I leveled and trimmed the aircraft and activated the Alt Hold function. It was now tracking the GPSS course and holding altitude. I'm thinking SWEET! It flew over TOMBS and then turned left to pickup the new course to E95 while maintaining altitude. All is well. Within 10 miles of E95, I disengage the autopilot's Altitude Hold to begin my descent and I make my first call to E95 traffic, providing all pertinent info. Within less than probably 30 seconds, my 430W displays a warning that it has lost GPS and to begin Dead Reckoning. DAMNIT!
I turn off the TT A/P at it's toggle switch. Nothing happens as far as the GNS430W reacquiring satellites. I turn my attention to making a safe approach and land at E95 and taxi to the run up area while I cycle the 430W. No Change, will not re-acquire the satellites. I shut everything down, and turn off the engine. Restart the 430W, no change, still will not re-acquire any satellite. Turn it off.
Decide to return to home base at KFHU. Go through my normal cockpit procedures as I restart the engine and turn all avionics back on, GNS430W will not acquire satellites.
Return to KFHU and land uneventfully. Taxi to my hangar and shut the a/c down with normal shutdown procedure, all avionics off, fuel pump off, avionics master switch off, master switch off, etc etc.
Sitting on the ramp, I turn everything back on with standard checklist procedures. The GNS430W RE-ACQUIRES all satellites and attains 3D differential position!!!! I program a flight plan in and activate it. Flight plan is active on 430W and EFIS. Engage the autopilot and initially have it fly the heading the airplane is sitting on. Then select GPSS Mode and it actuates the appropriate a/p servos to turn to GPSS course, GNS430W maintains satellites. Turn on the A/P Altitude Hold, GNS 430 maintains satellites and flight plan! Push the autopilot deactivate button on my control stick and then turn it back on to maintain current course, 070 degrees. Put the 430W on a COM Frequency not in the local area so as not to cause any problems with other pilots in the area and key the mike for several seconds, nothing happens to the GNS430w's flight plan or hold on satellites. Do it again and this time I notice on the TT A/P the course heading begins fluctuating upward and continues upward, increasing 16-17 degrees (to 86-87 degrees) from where it was initially, before I started keying the mike. Release the mike and the course heading returns to where it was, 70 degrees. Do it again, same outcome. Do it again, same outcome. Do it again, same outcome. All the time, the GNS430W flight plan and the satellites stay full acquired, green, no issues!
It seems now that I piece it together that as I was making my approach to E95 after turning off A/P Alt Hold but still allowing the TT A/P to follow the GPSS course, and making the traffic call, the transmitted power caused interference with the TT A/P (I didnt see any deviation on the display on the TT at that time) and somehow that appears to have also caused the GNS-430 to lose the satellites and as a result the flight plan course.
I have no idea why the GNS430W wouldn't reacquire the satellites at E95 (totally clear 360 degree view of the sky) but it did reacquire when I shut down and restarted everything again back at KFHU.
Thats the story! Obviously, I need to look at the antenna cable on the 430W and trace it to see if it is beleaguered in any way (Connectors, kinks, cuts, etc) and how close it is to any A/P servo or signalling line.

What else would you suggest? One thing which has come to mind is to program and fly a flight plan in the 430W and not allow the TT A/P to ever take control and see if keying the mike on it causes it to lose the satellite signals and drop the flight plan as a result.

Thanks for your continuing help Gentlemen.

Dan
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Dan L
N327CD
2004 RV7 and RV7A (birthed as a 7A, then 7 from 2006 until this past October and now RV7A again - has all mounts, gear, brake plumbing for both configurations)
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  #12  
Old 05-22-2022, 02:39 PM
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Carl Froehlich Carl Froehlich is offline
 
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Location: Dogwood Airpark (VA42)
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Default

Dan,

As an early GTN-650 adopter, I found I could make the GTN-650 loose all satellites simply by transmitting on the GTN-650. I also noted that when transmitting on Comm #2, the satellites where still there.

Digging into other reports, it seems the GTN-650, when transmitting, had harmonics being picked up by other avionics that then created noise at GPS frequencies. I believe Garmin specifically discussed this problem with ELTs.

My point, to see if this is the same issue you are having, transmit while watching the satellite reception page. Bring the other avionics on line on at a time and repeat. This is how I found my problem (my temporary Comm #2 - since replaced with the Dynon radio and all are playing nice now).

Carl
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  #13  
Old 05-22-2022, 03:14 PM
BobTurner BobTurner is offline
 
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Location: Livermore, CA
Posts: 8,226
Default

Next ground test don’t choose a random frequency. Use UNICOM for E95, where you had your problem.
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  #14  
Old 05-22-2022, 03:47 PM
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Dandlac58 Dandlac58 is offline
 
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Location: Sierra Vista
Posts: 44
Default

Hi Carl!

I appreciate you weighing in! I hope all is well - the trim indicator is working perfect! Thanks again.

That's some darned interesting information! Based on previous input from Bob, I tried transmitting on both Comm 1 and Comm2 as well as turning on the TT for course and ALT Hold while watching the Satellite Signal Page on the 430W. I did not detect any deviation. However, I will try it again and try it also with the frequency which seemed to have caused the problem as I approached E95 (122.8)
I also tried transmitting on Com2 (SL40) and did not detect any change in the course heading on the TT A/P, like I did when I keyed the 430W where I saw that drastic 16-17 degree deviation while keyed! I will check it again.

More to follow.

Dan

Quote:
Originally Posted by Carl Froehlich View Post
Dan,

As an early GTN-650 adopter, I found I could make the GTN-650 loose all satellites simply by transmitting on the GTN-650. I also noted that when transmitting on Comm #2, the satellites where still there.

Digging into other reports, it seems the GTN-650, when transmitting, had harmonics being picked up by other avionics that then created noise at GPS frequencies. I believe Garmin specifically discussed this problem with ELTs.

My point, to see if this is the same issue you are having, transmit while watching the satellite reception page. Bring the other avionics on line on at a time and repeat. This is how I found my problem (my temporary Comm #2 - since replaced with the Dynon radio and all are playing nice now).

Carl
__________________
Dan L
N327CD
2004 RV7 and RV7A (birthed as a 7A, then 7 from 2006 until this past October and now RV7A again - has all mounts, gear, brake plumbing for both configurations)
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  #15  
Old 05-22-2022, 03:53 PM
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Dandlac58 Dandlac58 is offline
 
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Location: Sierra Vista
Posts: 44
Default WILCO

Quote:
Originally Posted by BobTurner View Post
Next ground test don’t choose a random frequency. Use UNICOM for E95, where you had your problem.
Hi Bob,

WILCO and will forward results. Any idea why keying COM1 (430W) would cause the Heading course on the TT to drastically increase to 86/87 degrees (16-17 degrees) and then return to the course (070 degrees) it was on before keying?
And repeat the problem again and again, each time I key the 430W.

Thank you.

Dan
__________________
Dan L
N327CD
2004 RV7 and RV7A (birthed as a 7A, then 7 from 2006 until this past October and now RV7A again - has all mounts, gear, brake plumbing for both configurations)
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  #16  
Old 05-22-2022, 09:30 PM
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Dandlac58 Dandlac58 is offline
 
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Location: Sierra Vista
Posts: 44
Default Update, Evening 22 May 22.

Bob, Carl, Andrew,

I went back out to the hangar this evening to continue the ground test.

Did everything we talked about Bob and Carl, with same results, the only detected anomaly being when I keyed the 430W transciever to transmit, I saw the Heading degrees on the TT A/P increase while transmitting and then returning back to where it was when I released the PTT switch. I saw a similar result when keying the COM2 (SL40) radio although it wasn't as pronounced as the heading degrees on the TT display only increased 4-5 degrees. This occurred whether the TT was just powered on or powered on and tracking a heading or a GPSS signal.

The GNS got a good 3d Differential position fix and none of the satellites signals varied in strength as I keyed either radio and turned the avionics systems on and off. The activated flight plan stayed solid as well.

It seems like EMI from one or both radios and perhaps because the coax cables aren't good or maybe there is corrosion on a connector or a ground or an antenna? Something is clearly bleeding into the TT circuitry to cause the heading degrees (The top left degrees in the TT display) to increase while transmitting.

As a note of interest, all of the connections between the devices and to power and ground, etc are made with Approach Systems cables and their Fast Stack Pro-G Hub. Obviously the coax cables for the radios and the transponder do not go through the Hub. And the Uavionix Echo was added after years after the Pro G hub was installed so it is direct wired to power and ground and to its 978 Mhz antenna.

Thoughts and recommendations?

Thank you.

Dan
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Dan L
N327CD
2004 RV7 and RV7A (birthed as a 7A, then 7 from 2006 until this past October and now RV7A again - has all mounts, gear, brake plumbing for both configurations)
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  #17  
Old 05-23-2022, 08:33 AM
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Carl Froehlich Carl Froehlich is offline
 
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Default

Dan,

I would first focus on the 430.

You need to isolate everything. So one approach:
- Open the breakers on everything other than the 430.
- Disconnect the antennas (including ELT) from everything other than the 430.
- Key the 430 and watch GPS signal strength. If good, then bring back stuff one at a time and repeat.

I have found some radios are much better than others as for as front end selectivity (I know of one popular radio that is really bad for cross talk). Assume the 430 is the cause of your issues until you can prove otherwise.

As a backup check, repeat at all this for the SL-40.

Question - where is your 430 GPS antenna located, and how long is the coax run between it and the 430?

Let us know,
Carl

Last edited by Carl Froehlich : 05-23-2022 at 08:47 AM.
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  #18  
Old 05-23-2022, 09:14 AM
Dandlac58's Avatar
Dandlac58 Dandlac58 is offline
 
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Default Morning Update, 23 May 2022

Good Morning Carl,

All of the avionics, minus the Uavionix Echo, is connected to the Avionics Master Switch, so my only option is to not power them on at each individual device's on/off switch, which is what Ive been doing during testing.

Since I didn't build the airplane, I do not yet know the condition of the coax cables on the -430W, the SL 40, the GTX327 transponder, or even the Uavionix Echo.

I'm going to have to take the panel apart far enough that I can actually look at the cables and see what they are, they may not even be aviation grade shielded cables. And also pull the rear bulk head cover to take a look at the other end of the cables and their cable runs.

The GPS Antenna for the 430 is on the top of the fuselage behind the point to where the canopy rolls back rearward. The 430 comm antenna is on the fuselage underbelly, and is maybe too close to the the GTX327 antenna and the Uavionix 978 antenna.

My opinion is that keying the Com radio on the -430 is causing all kinds of problems, evidence being the way the TT displays the course degrees increasing up to 15-17 degrees as long as the PTT is activated. It seems that is causing EMI and creates conflicts between the TT and the -430W and perhaps the TT is sending that EMI back to the -430W on signalling lines? As a note of interest the PTT is the "trigger" switch on the Handgrip on the stick and the handgrip also has a button to disconnect the TT A/P and the "Hat" for the trim.

I have additional concerns about the SL40, and/or its coax, and/or its antenna, which is mounted horizontal orientation under the rear fairing area for the horizontal stabilizer and rudder, which I think is a poor choice as the antenna should be Vertical orientation, not horizontal. At this point, I have little confidence in it, and use it to receive ATIS or AWOS info only. Part of this operation will result in me getting rid of the SL40 and putting in a new Com2 radio, thinking maybe an SL30 with Nav capabilities too, or a GTR200, etc. But that's a side issue, got to figure out why the -430w is losing the Satellites and as a result the flight plan.

So anyhow, so far, keying the 430 does NOT change the GPS receive strength of the satellites (during several tests), but it does cause the rise in the Heading degrees on the TT A/P as previously indicated. The question is why is this happening? The second is what are the 2d, 3rd, and 4th order effects of that? I think I should try to connect a new coax cable between the -430W and its antenna and see if the issue on the TT A/P is corrected, that may correct everything?

Thoughts?

Dan



Quote:
Originally Posted by Carl Froehlich View Post
Dan,

I would first focus on the 430.

You need to isolate everything. So one approach:
- Open the breakers on everything other than the 430.
- Disconnect the antennas (including ELT) from everything other than the 430.
- Key the 430 and watch GPS signal strength. If good, then bring back stuff one at a time and repeat.

I have found some radios are much better than others as for as front end selectivity (I know of one propulsion radio that is really bad for cross talk). Assume the 430 is the cause of you issues until you can prove otherwise.

As a backup check, repeat at all this for the SL-40.

Question - where is your 430 GPS antenna located, and how long is the coax run between it and the 430?

Let us know,
Carl
__________________
Dan L
N327CD
2004 RV7 and RV7A (birthed as a 7A, then 7 from 2006 until this past October and now RV7A again - has all mounts, gear, brake plumbing for both configurations)
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  #19  
Old 05-23-2022, 10:32 AM
Carl Froehlich's Avatar
Carl Froehlich Carl Froehlich is offline
 
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Dan,

Just give me a call and we’ll discuss.

Carl
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  #20  
Old 05-23-2022, 12:41 PM
BobTurner BobTurner is offline
 
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Location: Livermore, CA
Posts: 8,226
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Side issue: Did you say that the wiring to your radios is not protected by CB s or fuses? That doesn’t sound good. But for Carl’s test, turning them off with their on-off switch should be okay.
Main issue: Are you saying you have not yet examined the coax connectors? Both radio end and antenna end? IMHO corrosion is often the root source of avionics problems. I still recall fixing an ARC autopilot by simply unplugging, and re-plugging, its connector in the wing. (Unplugging/re-plugging tends to scrape off a thin layer of corrosion. I would recommend getting hold of some spray-on contact cleaner, take apart every connection you can find (autopilot too) and spray it, re-assemble. These problems can be insidious, very hard to spot.

The SL30 is IMHO the best nav-com ever made. Unfortunately they have not been manufactured in many years, so they’re getting a bit long in the tooth.
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