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Interference between Com and Autopilot

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Peter.Sokolowski(at)t-onl
Guest

Posted: Mon Jan 16, 2006 11:43 am Post subject: Interference between Com and Autopilot

Hello all,

I am building my panel with a TruTrak DF II autopilot and 2 Becker AR3202 Coms. I have discovered that transmitting during engaged autopilot has influence on the AP in the form that the elevator goues up and the ailerons make a right turn. As the details on the up and down is second, the influence itself is of cause the problem. I have made the connections between the - high quality - HF cables and the BNCs myself (i.e. they should be OK) and use 2 standard - not self made - antennae.

The question is now - what can I do to avoid this interference? more shielding, replacing the autopilot, ...

BTW, the antennae are in the baggage compartment

Thanks

Peter Lancair 360 MKII 85%

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brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Mon Jan 16, 2006 5:05 pm Post subject: Interference between Com and Autopilot

Peter.Sokolowski(at)t-online.de wrote:

 	  Quote: 	
		   

 

 Hello all,

 I am building my panel with a TruTrak DF II autopilot and 2 Becker AR3202 Coms. I have discovered that transmitting during engaged autopilot has influence on the AP in the form that the elevator goues up and the ailerons make a right turn. As the details on the up and down is second, the influence itself is of cause the problem. I have made the connections between the - high quality - HF cables and the BNCs myself (i.e. they should be OK) and use 2 standard - not self made - antennae.

 The question is now - what can I do to avoid this interference? more shielding, replacing the autopilot, ...

 BTW, the antennae are in the baggage compartment


	


What are you using for a ground plane for your antennas?



Isn't the fuselage in the Lancair primarily carbon fiber? If that is the

case you are going to want to get the antennas outside the fuselage.



How does the TruTrak autopilot talk to its servos? Is is an analog

voltage or a digital message?



Frankly, I would talk with the folks from TruTrak. They can help you

with RF getting into their servos and/or the control head. Given the

digital nature of the TruTrak autopilot and if I understand their system

properly I would suspect that the problem is occurring at the one analog

point, where the analog rate-gyro signal is digitized.



But TruTrak is your best bet for assistance.



-- 

Brian Lloyd                         2243 Cattle Dr.

brian-yak at lloyd dot com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

- Antoine de Saint-Exupery

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_________________
Brian Lloyd
brian-yak at lloyd dot com
+1.916.367.2131 (voice) +1.270.912.0788 (fax)

I fly because it releases my mind from the tyranny of petty things . . .
- Antoine de Saint-Exupery

Peter.Sokolowski(at)t-onl
Guest

Posted: Tue Jan 17, 2006 11:06 am Post subject: Interference between Com and Autopilot

Hello Brian,

thanks for your response - please see my answers for simplicity reasons below between your mail. Problem still exists, today I have moved the cables a bit and the reactions changed. I will buy some ferit and try to put it on the servo cables. Will report results.

Peter

 "Brian Lloyd" <mailto:brian-yak(at)lloyd.com> schrieb:

 	  Quote: 	

 mailto:Peter.Sokolowski(at)t-online.de wrote:

 > 

 >

 > Hello all,

 > I am building my panel with a TruTrak DF II autopilot and 2 Becker AR3202 Coms. I have discovered that transmitting during engaged autopilot has influence on the AP in the form that the elevator goues up and the ailerons make a right turn. As the details on the up and down is second, the influence itself is of cause the problem. I have made the connections between the - high quality - HF cables and the BNCs myself (i.e. they should be OK) and use 2 standard - not self made - antennae.

 > The question is now - what can I do to avoid this interference? more shielding, replacing the autopilot, ...

 > BTW, the antennae are in the baggage compartment

 What are you using for a ground plane for your antennas?

45 x 45 cm glass fibre with copper on it

 	  Quote: 	

 Isn't the fuselage in the Lancair primarily carbon fiber? If that is the

 case you are going to want to get the antennas outside the fuselage.

not necessarily, there are 2 models. mine is made from glass

 	  Quote: 	

 How does the TruTrak autopilot talk to its servos? Is is an analog

 voltage or a digital message?

Honestly I do not know - I assume analog

 	  Quote: 	

 Frankly, I would talk with the folks from TruTrak. They can help you

 with RF getting into their servos and/or the control head. Given the

 digital nature of the TruTrak autopilot and if I understand their system

 properly I would suspect that the problem is occurring at the one analog

 point, where the analog rate-gyro signal is digitized.

Already done - that is one of the reason I asked the group. They have no solution - beside unbalanced antennae what I exclude.

 	  Quote: 	

 But TruTrak is your best bet for assistance.

 --

 Brian Lloyd                         2243 Cattle Dr.

 brian-yak at lloyd dot com          Folsom, CA 95630

 +1.916.367.2131 (voice)             +1.270.912.0788 (fax)

 I fly because it releases my mind from the tyranny of petty things . . .

 - Antoine de Saint-Exupery

- The Matronics AeroElectric-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

http://www.matronics.com/Navigator?AeroElectric-List

brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Tue Jan 17, 2006 12:44 pm Post subject: Interference between Com and Autopilot

Peter.Sokolowski(at)t-online.de wrote:

 	  Quote: 	
		   

 

 Hello Brian,

 thanks for your response - please see my answers for simplicity reasons below between your mail. Problem still exists, today I have moved the cables a bit and the reactions changed. I will buy some ferit and try to put it on the servo cables. Will report results.


	


It is always very annoying to troubleshoot RF getting into devices that

are not RF devices. EMI in telephones, stereos, and burglar alarms are

always a pain to troubleshoot.



Here are some things to try:



1. Try a ferrite bead over the entire servo wire at both ends.



2. Try ferrite beads over each individual wire in the cable at both ends.



3. Bypass the power wiring to ground at the head and at the servo using

.01 ufd disc ceramic capacitors.



4. Bypass the control signal lead at both the head and servo using a

.001 ufd disc ceramic capacitors.



5. Wrap several turns of the power wire around a ferrite toroid core

where it enters the control head and again at the servo.



I would try them in the order I have listed them. When working with the

disc ceramic caps you need to keep the leads as short as possible.



[sigh] RF in plastic airplanes is always a pain. I had a plastic car

once and tried to mount an antenna on it with a window-screen ground

plane. It never did work right.



Oh, something else to consider. You could try building a coaxial dipole

and mount that instead of using an aircraft antenna. The standard

aircraft antenna insists on a good ground plane. A coaxial dipole does

not need one but is twice as long.



-- 

Brian Lloyd                         2243 Cattle Dr.

brian-yak at lloyd dot com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

- Antoine de Saint-Exupery

- The Matronics AeroElectric-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

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BigD(at)DaveMorris.com
Guest

Posted: Tue Jan 17, 2006 1:39 pm Post subject: Interference between Com and Autopilot

This may not cure your RFI problem, but it might be an interesting 

alternative antenna in your fiberglass tailcone, as it eliminates the need 

for a ground plane and whip antennas, and conforms to the fuselage sides, 

leaving the interior open:



http://www.DaveMorris.com/MorrisComLoop



Dave Morris



At 01:05 PM 1/17/2006, you wrote:

 	  Quote: 	
		  



Hello Brian,

thanks for your response - please see my answers for simplicity reasons 

below between your mail. Problem still exists, today I have moved the 

cables a bit and the reactions changed. I will buy some ferit and try to 

put it on the servo cables. Will report results.

Peter

  "Brian Lloyd" <mailto:brian-yak(at)lloyd.com> schrieb:

 > 

 <mailto:brian-yak(at)lloyd.com>

 >

 >

 >

 > mailto:Peter.Sokolowski(at)t-online.de wrote:

 > > 

 mailto:Peter.Sokolowski(at)t-online.de

 > >

 > > Hello all,

 > > I am building my panel with a TruTrak DF II autopilot and 2 Becker 

 AR3202 Coms. I have discovered that transmitting during engaged autopilot 

 has influence on the AP in the form that the elevator goues up and the 

 ailerons make a right turn. As the details on the up and down is second, 

 the influence itself is of cause the problem. I have made the connections 

 between the - high quality - HF cables and the BNCs myself (i.e. they 

 should be OK) and use 2 standard - not self made - antennae.

 > > The question is now - what can I do to avoid this interference? more 

 shielding, replacing the autopilot, ...

 > > BTW, the antennae are in the baggage compartment

 >

 > What are you using for a ground plane for your antennas?

45 x 45 cm glass fibre with copper on it

 >

 > Isn't the fuselage in the Lancair primarily carbon fiber? If that is the

 > case you are going to want to get the antennas outside the fuselage.

not necessarily, there are 2 models. mine is made from glass

 >

 > How does the TruTrak autopilot talk to its servos? Is is an analog

 > voltage or a digital message?

Honestly I do not know - I assume analog

 >

 > Frankly, I would talk with the folks from TruTrak. They can help you

 > with RF getting into their servos and/or the control head. Given the

 > digital nature of the TruTrak autopilot and if I understand their system

 > properly I would suspect that the problem is occurring at the one analog

 > point, where the analog rate-gyro signal is digitized.

Already done - that is one of the reason I asked the group. They have no 

solution - beside unbalanced antennae what I exclude.

 >

 > But TruTrak is your best bet for assistance.

 >

 > --

 > Brian Lloyd                         2243 Cattle Dr.

 > brian-yak at lloyd dot com          Folsom, CA 95630

 > +1.916.367.2131 (voice)             +1.270.912.0788 (fax)

 >

 > I fly because it releases my mind from the tyranny of petty things . . .

 > - Antoine de Saint-Exupery

 >

 >

 >

 >

 >

 >

 >

 >

 >

 >

 >

 >

 >

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Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

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