EMS spikes etc

[jakej]

FWIW - I've been trying to help various people with the topic issues of 'spikes' when transmitting.  Now the obvious cause is RF, but why ?
All the installations I've done (including fitting the Com antenna) do not have a problem (except 1 composite aircraft) but a customer with an RV now does have issues although it was working ok for 6 months.  He had spiking when first flights began however he did some antenna bonding work and all seemed ok until just recently.

Yesterday the the light bulb came on - he fitted the antenna, not me.  There are only 4 screws & nuts, how hard is that to do ?  This is a reasonable question I think, but the answer is not necessarily straightforward.

So, IMO, this is what should be done when fitting a manufactured antenna eg Comant --- clean up the inside of skin where the attaching screw are, use thin star washers under the head of the screws and between nut and fuselage skin.  Then, after it's all assembled, spray some corrosion proofing product to protect the bare areas.   Do not remove paint from between antenna & skin, this is also the manufacturers advice.

Composite aircraft - do a SWR check of the antenna AFTER is is fitted, fiberglassing the antenna to fuselage will detune it so an SWR check must be done insitu &, in both cases above, use a low loss 50 Ohm cable eg RG400  - RG58/59 can/will give you heartache.

The above assumes you do not have any high current cables bundled with the rest of the wiring & all grounds and coax crimps are good ie the obvious things 

Hopefully the 'fix' is as simple as described, there is no more that I can add at this point.

Jake J

 

[dynonsupport]

And a note from us on this issue - we're looking at it from the engineering side as well. We don't have anything to report just yet in terms of preventative measures or a fix, but we think we're close to understanding the core issue here. We'll post more once we're more certain of things, though.

 

[preid]

Support
Thank you for that status.

 

[S-12]

I also have been dealing with egt spikes and vertical speed spikes when pressing the ptt. Dynon sent a capacitive filter for the adahrs. The filter worked for the vs spikes. I purchased a 25 pin 2200pf capacitive filter for the ems. It helped, but not completely. I was getting spikes that would X out the readings. Now I'm only getting a spike of 150-200 degrees. I'm going to try a 4000pf filter with some ferrites on egt wires and see if this solves it. Antenna coaxial is routed close to egt wires. I have limited space, Rans s-12. Antenna has a good ground and a swr reading of 2:1.

 

[korspich]

jakej im the rv builder you mentioned i think, i have cleaned all metal surfaces and fitted star washers at each end of the screw i have sprayed the bare surfaces with a little lanolin after fitting the screws . Perhaps when you are in my part of the country you could have a look.. you know how bad Rv builders are compared to Glasair types Also just noticed that the manifold pressure gauge also goes up about 5" when the ptt is pushed...amazing what you notice when you are parked in the hanger

 

[jakej]

Wally

In the hangar IS NOT the place to test, radiation (bouncing off the metal walls) back into the system is the issue :

Of the 28 Rv's I've done yours is the only one that has reported these 'issues'.

DS - Wally also reported that the filters worked for a while but they appeared to lose effectiveness. Is there any chance that the filters deteriorate due RF/EMI saturation ?

Jake J

 

[korspich]

i tested the"issue" in flight today and it is still the same . Tomorrow i will pull the cowls off and check all the blade connections from the sensors and clean them one by one

 

[jakej]

Save yourself the effort, that will not fix the 'spike' problem IMO

Jake J

 

[korspich]

I removed the radio from the stack and cleaned all the connections on the coaxial from the radio to the aerial using CRC CO contact cleaner. I read the instructions on the can very carefully and switched off everything electrical because it can be explosive in confined spaces. I then sprayed each connection (3 of them) then went and had a coffee while the fumes had time to disappear. When i tried the radio again the problem had decreased by about 75%. Instead of a 50+ degree spike on CHT and EGT it only went up about 8 to 10 degrees...further exploration required.

 

[jakej]

Wally

Good 'find' - note for others - the BNC connectors used on Wally's plane are the crimp type (IMO the clamp type come a distant second place) with gold plated contacts, coax is RG400.

Jake J

 

[korspich]

i spoke too soon ....after 1 hours flying and 2 landings problem was back again with off the scale readings on cht and egt.. until i landed at home base then the spike was the 10 degrees i mentioned before...any ideas? i am out of them.. :-/

 

[preid]

RV flyer and I have this issue, but not as bad as you have.
My suggestion for now, is Dynon is looking into this. Wait and see what they discover. Once we know what the issue may be we can all refocus on that component.

 

[korspich]

Thanks Reidvaitor i shall wait with bated breath for further developments

 

[PeterBain]

In the meantime while we wait with bated breath I take it that we are not doing any damage to our Skyview with all these spikes?
I am going on a long trip tomorrow and would hate to have a broken screen spiked out

 

[preid]

Only happens when you transmit.. right? you should be fine unless you are in a B airspace type environment (LAX, BOS) where radio comm is busy.
Dont look at the EGT when you press the transmit button and everything will be fine.

 

[PeterBain]

It's all in the mind hey

Updates take you one step forward and 10 steps backwards.
Come on Dynon let's have a fix to put our minds at rest this is not cool!

 

[dynonsupport]

Surfboy - no damage is being done when you see the spikes - It's only the reading which is erroneous. Thermocouples are sensitive to very small amounts of signal, so even small amounts of noise can have a drastic looking effect. We're working hard have a fix available.

 

[DennisW]

My problem has been reduced to about 15 degree spikes in my EGT CHT temp readings. I think I'll have to live with it. I got rid of the movement on my vertical speed indicator by installing a 9 pin L-Comm capacitive filter on the ADAHRS. I added extra ground wires from both the ADAHRS and EMS to ground the cases to my Ground Bus. It didn't make any improvement, but someone suggested it and I knew it couldn't hurt.

I have a composite airplane with dipole antennas from Advanced Aircraft Electronics. I am still living with RG-58 and will likely switch to RG-400 cable sometime in the future.

 

[dynonsupport]

As we said, we do expect to have a way to mitigate this soon. We'll keep you posted when we have an update. Until then, know that there's no damage being done, and when you're of the PTT button, the readings are accurate.

 

[RV6-KPTW]

Gosh,  having read some of these posts, I thought myself fortunate... Guess what!?!?  Between 98 and 99 flight hours (15 hours or more since upgrade to latest software) since install of new panel, I see this as well.  The cute little audio lady starts clammering about cht and other warnings as I am trying to transmit.  Additionally, the lean function freaks out - all somewhat predictable.

So did something change in my hardware and or connections?  Crimp going bad etc?

Thanks