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Why is my TruTrak knocking my GNS430 GPS Signal Offline?

Dandlac58

Well Known Member
I have a GNS430W in my panel, it is connected to a TruTrak DigiFlight Autopilot with Course or GPSS tracking and Altitude Hold.

The GNS430W works perfectly until I turn on my TT autopilot. Shortly after turning it on, I get a warning on my GNS430W that it has lost GPS signal and to begin Dead Reckoning navigation. I also lose GPS signal on my IPAD at the same time and it is getting GPS data and ADSB in from the Uavionix Echo in the panel!

If I turn off the A/P, the GPS signal returns and begins working correctly again. So it seems clear the A/P is causing the problem...

Anyone have any idea(s) about what is going on and how I can fix. I dont mind dead reckoning but I'd much rather let my autopilot fly the airplane while I maintain much better piloting and situational awareness over every aspect of the airplane, the airspace, etc.

Thanks in Advance.
Dan
 
I haven't ever heard of this before. Is the servo mounted very near the GPS antenna or is the GPS antenna coax routed very near the servo? From what it sounds like this isn't upon applying power to the autopilot, but upon engaging the servos. Is that correct?
 
Additional Information on Problem

I haven't ever heard of this before. Is the servo mounted very near the GPS antenna or is the GPS antenna coax routed very near the servo? From what it sounds like this isn't upon applying power to the autopilot, but upon engaging the servos. Is that correct?

Hi Andrew,
Thanks for working on this with me.
When I power on the Auto Pilot no problem. The problem occurs when:

I push the left button to select GPS course following,
and/or
Activate "Altitude Hold" function.

The reason I say and/or is because I didn't realize the auto pilot was causing the problem until near the end of the flight...(I was busy aviating, navigating, and communicating - I know you know...lol) so I'm not sure if the problem would have occurred if I only activated the a/p to follow the GPS course or if the problem only began when I activated Altitude Hold, or if the problem only occurred because I activated both functions. I hope that makes sense.

The GPS antenna is mounted on the top of the fuselage right behind the canopy at its farthest rearward location. I do NOT know if the GPS coax is near the servo... I did not build the airplane, I bought it from the gentleman who bought it from the gentleman who built it (I am not a builder, just a flyer but I do have some mechanical and electrical experience and knowledge!) Which servo are you talking about? Im assuming the altitude hold servo - where is the servo likely to be located?

Next thing I will do is fly the airplane again next week and fly the airplane with the autopilot following a compass course only (i.e. 150 degrees), then following a GPSS course and see if we get the failure. Then turn on Altitude Hold and see what happens. See if I can troubleshoot it down to a specific function.

Thanks
Dan
 
Ground check

Put your 430W on the ‘satillite signal strength’ page (top, far right on the page matrix). Observe the bar heights. Turn on the various autopilot functions, watch for the bars to go down. If/when they do, it means that autopilot function is radiating a signal that interferes with the gps signal. Do you have any other gps units that come on only with the autopilot?
 
Bob offers very sound advice above.

The pitch servo is mounted just aft of the baggage compartment near the pitch reversing bellcrank. Let me know when the issue occurs and we can dig into what might be causing it.
 
Put your 430W on the ‘satillite signal strength’ page (top, far right on the page matrix). Observe the bar heights. Turn on the various autopilot functions, watch for the bars to go down. If/when they do, it means that autopilot function is radiating a signal that interferes with the gps signal. Do you have any other gps units that come on only with the autopilot?

Great Idea Bob. I should be able to try that on the ground too, after the 430W has established a 3d position.

My GRT EFIS I believe has its own GPS and I know my Uavionix Echo has its own GPS which also feeds position info to my EFB on my IPAD and as I said it fails (the GPS data on the IPAD) at the same time as the GPS in the 430W. In fact I initially thought it might be the WIFI between them which was knocking out the GPS since I thought it might be causing too much interference for the low power GPS signals.
The power for the EFIS and the Echo comes on when I turn on main power breaker for the airplane. The fellow who owned it before me didnt put the Echo on its own circuit breaker... I am going to change that so I can turn it on and off independently.
 
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Bob offers very sound advice above.

The pitch servo is mounted just aft of the baggage compartment near the pitch reversing bellcrank. Let me know when the issue occurs and we can dig into what might be causing it.

I will do that after I have tried Bob's idea and my own, although will I be able to set Altitude Hold to "ON" in the TT without it being airborne and moving? I have a two mile taxiway I could use at KFHU if I just need to be moving...
I will also inspect the pitch servo for proximity to the coax for the GNS430W antenna.
 
Update

Yes, you can engage the entire system on the ground and do not need to be moving.

Hi Andrew,

I pulled my a/c out of the hangar so the GPS antenna had a clear view of the sky.

I powered on the 430W and let it boot and waited for it to get a 3D position. I then watched the satellite receive page where it showed that all Sats it was receiving were green with a "D" designation (showing it was getting correction information).

I then turned on each (and every) other system one at a time, to determine if it might cause a reduction in GPS signal strength. I turned each system off before turning another on. This included my GTX327, SL40, Uavionix Echo, IPAD and TruTrak autopilot, dual emags. The GRT Sport EFIS was always on.

No reduction in GPS signal strength.

I then turned all systems on and taxied the airplane around the airport, no reduction in GPS receive signal strength.

Next test is to go up for a flight to see if the problem re-occurs while in-flight.

More to follow.

Dan
 
Update

Put your 430W on the ‘satillite signal strength’ page (top, far right on the page matrix). Observe the bar heights. Turn on the various autopilot functions, watch for the bars to go down. If/when they do, it means that autopilot function is radiating a signal that interferes with the gps signal. Do you have any other gps units that come on only with the autopilot?

Hi Bob,
This is my follow-up post to Andrew:

Hi Andrew,

I pulled my a/c out of the hangar so the GPS antenna had a clear view of the sky.

I powered on the 430W and let it boot and waited for it to get a 3D position. I then watched the satellite receive page where it showed that all Sats it was receiving were green with a "D" designation (showing it was getting correction information).

I then turned on each (and every) other system one at a time, to determine if it might cause a reduction in GPS signal strength. I turned each system off before turning another on. This included my GTX327, SL40, Uavionix Echo, IPAD and TruTrak autopilot, dual emags. The GRT Sport EFIS was always on.

No reduction in GPS signal strength.

I then turned all systems on and taxied the airplane around the airport, no reduction in GPS receive signal strength.

Next test is to go up for a flight to see if the problem re-occurs while in-flight.

More to follow.

Dan
 
The Plot Thickens...

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
 
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
 
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

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
 
WILCO

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
 
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
 
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
 
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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



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
 
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.
 
Morning Update, 24 May 22

Hi Bob,

There are no schematics for how this panel is put together, so I am essentially learning it as I go.

There are no individual circuit breakers on the panel for the individual NAVCOM devices, the transponder, etc. What there is, is a Master Avionics Breaker which feeds to two "submaster" Avionics breakers which then each provide power to different pieces of the stack. The TT A/P is on its own separate circuit breaker - go figure!~

I cannot say for a fact, yet, that there are not fuses on the power lines going to each device.

I have now discovered that there is RG58 coax for the COM radio on the GNS430W and it terminates in the tail cone on a ratty horizontally polarized antenna... the coax has a severe bend in it at the rear of the fuselage as it leaves the belly and transitions up to where the antenna is mounted. I am having my A&P fabricate a test coax of RG400 which I will use first to test continuity of the current RG58 shield and center conductor and then to replace the RG58 and make a quick run directly between the radio and antenna mostly outside of the aircraft, away from all other power and signal lines to see if it clears the problem on the TruTrak.

Notes of interest:
a. The cable for the GSN430W GPS antenna is RG400.
b. The cable for the GNS430W Nav is RG400 and goes to a splitter which then goes to the Comant CI122 antenna mounted on the belly.
c. The cable for the GNS430W G/S connector goes to the other connector on the splitter (it is a 2 down to 1 splitter) and so therefore goes to the Comant on the belly.

Apparently the SL40 coax goes to an antenna in one of the wingtips, something which I must visually prove!

More to follow.

Thanks

Dan


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.
 
Hi Bob,

There are no schematics for how this panel is put together, so I am essentially learning it as I go.

There are no individual circuit breakers on the panel for the individual NAVCOM devices, the transponder, etc. What there is, is a Master Avionics Breaker which feeds to two "submaster" Avionics breakers which then each provide power to different pieces of the stack. The TT A/P is on its own separate circuit breaker - go figure!~

I cannot say for a fact, yet, that there are not fuses on the power lines going to each device.

I have now discovered that there is RG58 coax for the COM radio on the GNS430W and it terminates in the tail cone on a ratty horizontally polarized antenna... the coax has a severe bend in it at the rear of the fuselage as it leaves the belly and transitions up to where the antenna is mounted. I am having my A&P fabricate a test coax of RG400 which I will use first to test continuity of the current RG58 shield and center conductor and then to replace the RG58 and make a quick run directly between the radio and antenna mostly outside of the aircraft, away from all other power and signal lines to see if it clears the problem on the TruTrak.

Notes of interest:
a. The cable for the GSN430W GPS antenna is RG400.
b. The cable for the GNS430W Nav is RG400 and goes to a splitter which then goes to the Comant CI122 antenna mounted on the belly.
c. The cable for the GNS430W G/S connector goes to the other connector on the splitter (it is a 2 down to 1 splitter) and so therefore goes to the Comant on the belly.

Apparently the SL40 coax goes to an antenna in one of the wingtips, something which I must visually prove!

More to follow.

Thanks

Dan
A few thoughts:

1. Hopefully the builder understood that every wire downstream of the breaker must be able to carry the full breaker current limit. That means the individual wires to the avionics must be larger than normally used.
2. Hopefully your com antenna is vertically polarized, not horizontal.
3. Look at the connectors for any corrosion. Rule 1 of trouble shooting: always do easy stuff first, even if unlikely.
4. Coax with a sharp bend is asking for trouble, now or later. RG400 is relatively expensive, so save a few dollars and rather than have your mechanic fab a test piece, just replace the RG58 now.
5. Your ‘splitter’ (which technically is a simple 1 into 2 device) is probably a ‘diplexer’ (which splits 100 MHz into one output, 300 MHz into the other). The difference is rarely important except for distant VORs. But check that the connections are correct (antenna, VOR/LOC, GS to the corresponding antenna and 430 inputs)
6. The wingtip com antenna must also have as much vertical throw as possible in its leading edge, or performance will be poor.
 
Ive got the airplane all apart now...

Hi Bob, Carl, Andrew,

... with both wingtips off, floor panels out, rear bulkhead covers removed... so I can start replacing cables.

Priority 1:
a. Replace GNS430 Com RG400 Cable to new RG 400 and install on Comant Vertical polarized Antenna on belly.
b. Replace RG58 cable running from the GPS connector on the GNS 430 to the GA35 GPS antenna on the top of the fuselage.

Priority 2:
a. Add a stand alone circuit breaker to the Uavionix Echo ADSB In/OUT box so I can independently control power to it instead of powering it with one of the Avionics Masters as it is currently configured. This way I can check and see if either the ADSB 978 Mhz Out or the WIFI to my IPAD is causing any EMI. The Echo was added by the previous owner as part of the purchase agreement and it wasn't really installed up to standard of Part 43.
b. Replace the RG58 with RG400 on the SL40 and add a new antenna on the fuselage to replace the hokey one in the wingtip.

Priority 3: Before resuming flight, run new RG400 from ELT to antenna to replace the bad RG58. Replace batteries in ELT.

I haven't heard from Andrew as to the possible causes why the TT A/P is displaying the heading compass degrees rising by up to 17-19 degrees just because I am keying the radio. As soon as I stop keying the displayed degrees goes back to where it was before keying the mike. Im hoping changing out all these cables and re-routing them will solve it.

Dan
 
Hall Effect Current Sensor, etc.... Success!

So, to close this out:
I replaced the RG58 on my two Com Radios (GNS430 and SL40) with RG400. Checked for continuity and resistance. GTG.
I installed two new AV-17 Com Antennas on the belly behind the luggage space so they were far removed from the Panel. Also because the AV17 has a network in the base, you cannot test them for DC continuity. Previously Com 2 was connected to poor antenna in the pilot side wingtip and the Com1 radio was connected to an AV17 antenna on the belly underneath the passenger seat and far too close to the Transponder and ADSB OUT antennas - within about 6 inches.
I replaced the RG58 with RG400 on the GNS430's GA35 GPS antenna.
I discovered a Hall Effect Sensor (for the GRT EIS) installed behind the panel and on the main power cable from the battery. The previous owner wrongly installed it here. GRT says best is to mount it on the Alternator output cable to monitor and measure the amount of current it is sending to the AC and battery or alternatively - and second best location, mount it on the Positive battery cable in the engine compartment, not inside the cockpit behind the panel.
Also followed the TruTrak procedure to re-calibrate the internal magnetometer in the Digiflight II autopilot.
After doing all of this, SUCCESS, Auto Pilot and GNS430 working as advertised and it is a joy to fly! I think the biggest problem was the AMPLOC100 wrongly installed behind the panel on the battery cable instead of in the engine compartment on the alternator output cable and it was causing too much magnetic interference.

Whoop Whoop!
Thanks to Carl and Bob for their insights and input to resolving this problem.
 
RE: Hall Effect Current Sensor, etc.... Success!

Hi Andrew,

It may have been a combination of many things, because as you may recall, the heading reading in the Digiflight II would rise about 20 degrees during transmission of the Com radio of the GNS430. Then would go back down upon releasing the PTT,
It appears that doing all the actions I took, including getting the hall effect sensor out (it was within just a couple of inches of the back of the Digiflight II, may have in totality made the difference. I have not yet reinstalled the hall effect but when I do it is going in the engine compartment and away from the avionics panel.

Thanks.

Dan
 
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