Comm RF interference with altitude reading

[fly3g]

Symptom:  I have a ~+300 foot altitude deviation on the Skyview EFIS display anytime the COM radio is keyed to transmit, no other EFIS indications are affected. Altitude reading returns to normal after transmit stops.

Configuration:
Skyview V14
GTR200 COM
Coax RG400
Skyview network cable at one point in path runs parallel in separate plastic conduit to coax for ~3.5 feet, separation distance ~1"
Wood aircraft construction

Test experiment note:
Hooking up a separate coax cable running ~24" away from original cable run produces no altitude misread

Hypothesis:  close proximity of network cable and coax over the 4 foot section is producing RF interference into network cable

Questions:

Shouldn't the shielding in RG400 prevent this issue?

Why is only the altitude reading affected and not the other ADAHRS readings (compass, airspeed, etc) that are transmitted over the network cable.

What is the minimum distance between RG400 and Dynon network cable is acceptable?  Due to limitations of fuselage design may only be able to relocate coax ~4" away from network over the 4 foot run section.  Cannot currently recreate this configuration experimentally to test before implementing.  Difficult to do any cable rerouting in aircraft so would like to have a good feel any reroute effort will be successful before trying.

Anything else to look at or try before doing the major surgery to move the coax and hope for the best with the additional 4" spacing?

Thanks for any ideas.

Gregg

 

[dynonsupport]

Greg:

The Radio Frequency (RF) energy isn't affecting the data being transmitted ON the SkyView Network cable (only altering the "bits" for altitude). What's happening is that the RF energy is finding its way into the ADAHRS module and affecting the pressure sensor for the Static port or the input on the chip that converts the analog voltage out of the pressure sensor into digital data.

This happens very rarely. Unfortunately, every experimental aircraft is one of a kind, so we don't have the blanket recommendations you're asking for.

If you install this unit - http://www.l-com.com/d-sub-capacitive-filter-emc-adapter-db9-male-female between the ADAHRS module and the SkyView Netwwork cable, it may help. EMC in the title stands for "Electro Magnetic Compatibility" also known as EMI - Electro Magnetic Interference or RFI - Radio Frequency Interference. Using this unit has helped an aircraft manufacturer that had a situation similar to yours (where they could not alter their wiring). Please let us know if that helps.

Symptom:  I have a ~+300 foot altitude deviation on the Skyview EFIS display anytime the COM radio is keyed to transmit, no other EFIS indications are affected. Altitude reading returns to normal after transmit stops.

Configuration:
Skyview V14
GTR200 COM
Coax RG400
Skyview network cable at one point in path runs parallel in separate plastic conduit to coax for ~3.5 feet, separation distance ~1"
Wood aircraft construction

Test experiment note:
Hooking up a separate coax cable running ~24" away from original cable run produces no altitude misread

Hypothesis:  close proximity of network cable and coax over the 4 foot section is producing RF interference into network cable

Questions:

Shouldn't the shielding in RG400 prevent this issue?

Why is only the altitude reading affected and not the other ADAHRS readings (compass, airspeed, etc) that are transmitted over the network cable.

What is the minimum distance between RG400 and Dynon network cable is acceptable?  Due to limitations of fuselage design may only be able to relocate coax ~4" away from network over the 4 foot run section.  Cannot currently recreate this configuration experimentally to test before implementing.  Difficult to do any cable rerouting in aircraft so would like to have a good feel any reroute effort will be successful before trying.

Anything else to look at or try before doing the major surgery to move the coax and hope for the best with the additional 4" spacing?

Thanks for any ideas.

Gregg

 

[fly3g]

Thanks for the explanation.  Will try the inline filter and report back.  Gregg

 

[fly3g]

I believe the filter recommended is doing the job.  After installing I still see a small altitude change during radio transmission of maybe at most 10 feet.  If I move the plane out of the hangar (metal) the response to the radio transmission appears to be 0.  Since I don't do a lot flying in the hanger for now I will claim the filter unit has fixed the problem.  Thanks Dynon for a relatively painless diagnosis and solution.

 

[dynonsupport]

And thanks for letting us know that it seems to have worked.

I believe the filter recommended is doing the job.  After installing I still see a small altitude change during radio transmission of maybe at most 10 feet.  If I move the plane out of the hangar (metal) the response to the radio transmission appears to be 0.  Since I don't do a lot flying in the hanger for now I will claim the filter unit has fixed the problem.  Thanks Dynon for a relatively painless diagnosis and solution.

 

[Pilotkms]

Re: Comm RF interference with alt. reading(EMS for me)

I have a similar issue.   on both my GTN650 and SL40, when i key the mic the EGT & CHT indicators go off the scale to 600 - 1000 degrees.  in searching for the cause & solution i attached ferite RFI filters onto the sensor wires about 6" from the EMS box.  this helped.  it reduced the temperature indications increase to ONLY 140 degrees.  its 75 degrees out so still not acceptable.  i'm going to try an RFI filter as suggested but am still wondering if there is some EMS setting that i overlooked that would by chance fix this??  there are lot of these flying and there doesnt seem to be a lot of RF problems - or are there??

 

[jakej]

I have a similar issue.   on both my GTN650 and SL40, when i key the mic the EGT & CHT indicators go off the scale to 600 - 1000 degrees.  in searching for the cause & solution i attached ferite RFI filters onto the sensor wires about 6" from the EMS box.  this helped.  it reduced the temperature indications increase to ONLY 140 degrees.  its 75 degrees out so still not acceptable.  i'm going to try an RFI filter as suggested but am still wondering if there is some EMS setting that i overlooked that would by chance fix this??  there are lot of these flying and there doesnt seem to be a lot of RF problems - or are there??

Contact DS, you may have to return the EMS module for a 'fix'.

 

[Pilotkms]

Will do first thing in the morning.  i have tried a lot of methods and verified how it all works so thats about the last thing i was thinking too. 
thanx for quick response - and from the other side of the world - AMAZING.

 

[jakej]

You're welcome

Some of the earlier EMS units needed returning to Dynon to 'fix' the issue.

 

[dynonsupport]

Jake always seems to be on duty on the Forum! As always, thanks for the assist, Jake!

You called Dynon Avionics Tech Support and we issued an RMA to send you a replacement SV-EMS-220.

Note that when we tried to send you a confirmation email, it bounced - you might want to check with your email provider, or call Dynon Avionics with a different email address.

Will do first thing in the morning.  i have tried a lot of methods and verified how it all works so thats about the last thing i was thinking too. 
thanx for quick response - and from the other side of the world - AMAZING.

 

[dlloyd]

The original poster later mentions the problem seems to go away completely outside the hanger. At some point I had everything turned on inside my hanger, put the headset on...what the heck? Never heard all that before! I think my radio even picked up noise from the lighing. Problem persisted until pushing the plane five feet out of the hanger door. Point is, you can not evaluate EMI inside a steel box that bounces everything back to you.

 

[Pilotkms]

So yes- turns out that this is a known problem.  Dynon shipped me a replacement and this problem is no longer.
thanx Dynon!