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jiott
10-25-2015, 06:58 PM
I have a Dynon Skyview in my Kitfox with 912ULS engine. I use the Dynon EMS (engine management system) module with all Dynon supplied engine sensors for the Rotax engine. The amps sensor is a Dynon supplied shunt feeding into the EMS module. My amp readings on my Skyview engine page are always normal and consistent EXCEPT for one situation: When I press the push-to-talk button to transmit on my Garmin SL-40 radio, the amp readout goes wild showing negative values winding up to 40-50 amps! Of course these values can't be real and I have ignored them for 2 years now. It has done this since day one, and the readings immediately go back to normal after I quit transmitting on the radio. No breakers ever trip and no smoke or damage of any kind has occurred.

I submitted this "problem" to the Dynon tech support people and they think it is due to the RF energy from the radio interfering with the very sensitive ammeter sensor wires (unshielded). The sensor uses only a few millivolts/amp. My radio antenna is mounted on the bottom of the fuse and I use the hi quality RG400 coax cable from radio to antenna. This cable does run within about 6" of my EMS module. Dynon suggests I try moving the antenna cable routing farther away, but I am hesitating because it is not an easy job and that cable is very well shielded.

So here is the question for you electrical gurus out there: Have any of you heard of this before or known anyone who had to deal with it? What did they do, or what would you do. I am very strongly inclined to continue to ignore it as I have been for 2 years. Do you see any potential problem with doing that?

Av8r3400
10-25-2015, 08:18 PM
Do your push to talk leads pass near the shunt?
Does the antenna lead pass near the shunt?

What does pass near the shunt for wiring?

Av8r_Sed
10-25-2015, 08:55 PM
This could be a good application for a snap-on ferrite bead located on the sense lines near the shunt. They kill RF while letting low frequency signals pass. 10044

jiott
10-26-2015, 10:08 AM
The PTT leads do not pass anywhere near the shunt. The radio antenna cable also does not pass near the shunt. The items/wiring that are near the shunt are: voltage regulator, transponder and its antenna cable, capacitor.

Where do you get the ferrite beads/what brand are they-looks interesting.

kitfox2009
10-26-2015, 11:15 AM
G`morning Paul and others

I have Vixen 912UL. All older round gauges. A210 radio and Terra transponder. Avshop after market Lightspeed headsets.

Occasionally I get feedback when on transmit to the point that radio is unusable. I try an old DC and all`s well. Then go back to my Lightspeed and all`s well. When flying last week with a friend and 5 headsets, kept changing them around and everything was fine. (the Bose won, hands down!!). Anyway just wondering if these "ferrets" would help this situation and if so does anyone have an idea as to what type and where I would place them.

Radios and headsets are a total mystery to me and there appears to be quite a bit of knowledge and experience on this forum.

Right now everything is just fine but you never know "it just might start squealing" again. May not happen til next year.

Thanks
Don

kitfox2009
10-26-2015, 11:16 AM
That should "ferrite"

Av8r_Sed
10-26-2015, 07:00 PM
Ferrite cores are carried by the major electronics distributors such as Mouser and Digi-Key. You can get split cores that can be snapped around an existing cable / conductor or plain cores where you have to thread the conductor through them. Effectiveness can be increased by making multiple turns of the conductor through the core. You probably want to select one that's effective around common com frequencies like 122.8 MHz. Make sure the hole in the ferrite will accommodate the conductors you want to pass through it. For the ammeter application, you might want to pass both sense leads from the shunt through the ferrite.

You'll have to sort out minimum order and shipping prices.

Here's a link to one datasheet: http://www.mouser.com/ds/2/212/KEM_E5005_ESD-SR-372794.pdf

Note: I don't have any noise issues on my Model III and haven't used these in aircraft service.

Kurt.A
11-01-2015, 09:30 AM
I agree with Paul's advise. Another couple ideas you could try would be to twist the wires together that go to the PTT switch. Twisting together allows cancellation of magnetic flux generated by the collapse of the field. Another idea would be to place a schottky diode across the PTT switch which would allow any field collapse to be dispersed within the wiring.

jiott
11-01-2015, 05:26 PM
Kurt, my problem occurs from the time I push the PTT switch until I release it. As long as I hold the switch my ammeter readings go wild. Your suggestion would seem to apply only if the problem occurs momentarily when the PTT switch is pushed or released. Do you agree or still stand by your suggestions?

Kurt.A
11-06-2015, 01:06 AM
Jim,
I did indeed get the wrong impression from your first post. The suggestions I gave would solve only for wild amp meter readings during opening or closing of the PTT switch. Not while holding the switch depressed.

Dave S
11-06-2015, 07:09 AM
Jiott,

I have been reading this post with a degree of intrigue..........and I haven't responded till now because my line of thinking might be percieved as voodoo........


Your comment about the response from Dynon....."I submitted this "problem" to the Dynon tech support people and they think it is due to the RF energy from the radio interfering with the very sensitive ammeter sensor wires (unshielded). The sensor uses only a few millivolts/amp." I think has validity......although what they did not say, according to your post, exactly how or where the RF may be coming from.

Here is my voodoo story.......none of our aircraft are exactly the same; and, consequently, none of our experiences are likely to be identical......:confused: So.....when I was assembling our aircraft and doing final testing while not everything was quite complete...I was playing with the radio.....everytime I keyed & held the PTT.....the little red LEDs I had mounted up by the wing roots for nightime cockpit illumination came on!.....Voodoo because the LED wires were not yet connected to anything!....just the unshielded electrical wires laying across across the carrythrough tube by the front of the turtledeck. This was not my imagination...it happened......suspected cause.....the location of the com antenna behind the turtledeck was just a few feet from where the loose wires were laying was apparently enough to induce enough voltage in the wire to light up the LEDs (which have an extremely small draw in order to light up). With the LED feeds rerouted under the sheetmetal & connected to the buss/switch the issue went away - since I really, really wanted to have the LEDs come on at times in addittion to when the PTT was activated!

With my little light voodoo story.....although different equipment is involved from your situation...you might consider the RF source interfering with the ammeter reading could be coming right off the exterior comm antenna and not from the antenna cable leading through the airframe. Might be just the way ammeter sensor wires are run through the aircraft in light of the fact that the whole aircraft is bathed in concentrated radiation from the comm antennae when the PTT is activated.

Can't say that it is possible to diagnose stuff like this from a distance...lord knows we can't see RF waves with out eyes:(....just a thought for consideration.....The Dynon folks might be onto something with their RF interference comment.....location of the unshielded ammeter sensor wires might be worth considering....or using a shielded wire.

Just a thought for consideration.

Dave S
KF 7 Trigear
912ULS Warp Drive

JohnF
11-06-2015, 09:51 AM
Not a guru. Just my opinion.

Your antenna system is probably not balanced. (pretty tough to do on a kitfox)
The antenna is a series circuit so the current on each side (the whip and the ground plane) have to match and to do this your coax shield is probably an active element in the antenna system.

Besides being an annoying signal on the sense lines of the ammeter it probably isn't all that good for your radio. (although they can deal with some reflection)

A tuned ferrite toroid is a good idea. I would put it on the coax as near to the antenna as I could. Each trip a coax makes through a toroid will remove about 90% of the common mode signal (the reflected part) and none of the differential mode signal (the part you want to get to the antenna). to get 99.9% of the reflections removed you could wrap the coax through the same toroid 3 times or put 3 toroids in a row (maybe a 1/4 inch apart so they don't act as one detuned toroid.)

THat's what I would try, 3 toroids on the coax near the antenna. Use shrink wrap, hot glue, rtv, electrical tape to fix them so they don't move about and make sure they are supported so as to not add strain on the coax run. I have seen them for sale on the MGL web site.

jiott
11-06-2015, 08:48 PM
Thanks Dave and John, I have been thinking about rerouting the sensor wires and using shielded wires. I also have been looking at ferrite toroids and snap-on beads. I plan to experiment with some of these methods. Will report on the results.

Esser
03-15-2019, 03:47 AM
At update on this Jim? My fuel pressure is going up when I use my PTT amongst several other little things.

jiott
03-15-2019, 09:23 AM
I installed two ferrite toroids and it didn't make any difference. I have just been living with it; it hasen't seemed to hurt anything.

PapuaPilot
03-15-2019, 07:35 PM
At update on this Jim? My fuel pressure is going up when I use my PTT amongst several other little things.

Too bad it's not your fuel quantity. ;)

Esser
03-15-2019, 08:04 PM
I fixed it. Rerouted my COAX and it went away.

efwd
03-15-2019, 08:23 PM
Nice Phil ;)