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marchudson 10-17-2010 10:15 PM

Running out of ideas
On how to fix the problem with RFI/EMI.

Components that I have:

GNS430W (Comm 1)
SL-40 (Comm 2)
RG-400 coax cable
2 - RAMI bent whip antennas mounted on belly
Dynon Skyview with EMS module
Single point ground for everything.

Problem I'm having:

When I transmit on comm 1 AND comm 2, the EMS readings go nuts. CHT/EGT moves anywhere from 10 deg to 100 deg depending on the frequency that I'm transmitting. If transmitting on 118.0 I'll get just a little change, on 136.0, I get a huge change. When transmitting on 124.0, the ammeter goes from +8 amps (normal) to -35 amps. Talked to the Dynon folks and they said that I'm the only one with this problem?????

Solutions I've tried:

1. Replacing both cables with store bought cables and routed them in random locations to see if this makes a difference. (no difference noted)

2. Power the Dynon with just the standby battery (no difference). Note Dynon system is still tied to aircraft ground system.

3. Disconnect the sensor wires from the EMS. result - system behaves normally but I don't have any engine monitor readings either. (Maybe noise is not entering EMS module on power supply lines)

4. Place a 12" X 12" piece of aluminum foil on the antenna, touching nothing else but the antenna. (normal indications - I deduce by this that the coax is probably not leaking due to this, don't know)

5. Transmit on Comm 1 and compared results to transmitting on Comm 2. Both radios produce the same adverse results on the EMS.

My next step is to place ferrite chokes on the 3 EMS cables. But is this just putting a bandaid on the problem? I would rather fix the root problem.

OK... I'm open for suggestions. Do I need to purchase a SWR meter or purchase a different brand antenna?

Thanks for your time

Norman CYYJ 10-17-2010 10:37 PM

Make sure that the antennae are properly grounded to the airframe. The base of the antennae need to be bonded where they are mounted. It does sound as though you have extremely high VSWR and a poorly grounded antenna can do this. Good luck.

AltonD 10-18-2010 12:32 AM

Grounds. Make sure you have a very good ground from all components, including the engine. Did you use a ground block or are your components grounded via the frame?

scsmith 10-18-2010 12:47 AM

antenna ground
I agree, its the first thing I thought of. The antenna is not grounded at its mount, and/or the shield braid of the RG-400 is not grounded to the connector(s).

Try leaving the engine thermocouples connected to the Dynon, but not plugged into their spots on the engine. So the probes are just hanging in the air. That way, the probes can not pick up any ground noise. If they still act up, the noise is coming in through the power and ground leads to the Dynon. If they are quiet, you know the noise is coming into the probes. Either way, you are putting a lot of energy into the ground somewhere.

marchudson 10-18-2010 07:05 AM

Thanks for the quick replies guys. My initial thought was also the ground. My first action was to check the continuity of both antenna bases to the airframe and I am getting zero resistance. The engine is grounded to the airframe via a #2 welding cable and I checked the resistance from several locations on the engine to the grounding block, zero ohms. As far as the coax shield grounding is concerned, I checked both with the meter and then removed them from the equation when I temporarily replaced them with store bought RG-58 cables.

Steve - I actually tried your idea of unplugging a few of the CHT probes from the engine. When they are left near the engine but not touching anything I get the same results. If I let the probes dangle below and very near the main gear, the problem gets much worse. I figured that they are in the direct path of the radiated energy when dangling.

Alton - yes I have a single point ground for all equipment in the aircraft and everything is running to it.

Sounds like guys think I might need to get an SWR meter to determine the health of the antenna / cable combination.

R.P.Ping 10-18-2010 08:21 AM

Bounce back
I had some initial problems when I was checking systems out in my garage. Just couldn?t get the led lights not to glow when I transmitted. Checked grounds, moved antenna wires, checked antenna connections. Ended up it was the signal bouncing around inside the garage. All my work trouble shooting was for nothing. If you can move your project outside it will probably work just fine.

Ironflight 10-18-2010 08:25 AM

Have you checked with Dynon on this? I have had two builders talk to me about RFI and their Skyviews. Both were working with Dynon to solve the problem, with varying results. This might be a case of new hardware (the Sky view is still pretty young) going through some early learning stages.


Mel 10-18-2010 08:31 AM

Marc, I believe you are located at Caddo Mills. If this is the case, I have an SWR meter that you may borrow. I'm at ShortStop Airfield less than 10 miles north of you.

rich 10-18-2010 08:48 AM

I had the same problem with my SL-40 and RMI eng. monitor.
When I would transmit the RMI CHT/EGT readings would go nuts and set off alarms.
Take a hand held com and while transmiting run it up and down your wire bundles and observe your EMS. When the numbers start to change you found a "LEAK" where RF can enter. I found my worst leak where the CHT/EGT'S connect to a rotary switch . I wrapped some braided shielding around the area so at least the alarms don't go off now.
I too have everything grounded to a grounding block on the firewall.
If you find the "FIX" let me know.
Good luck,

kalaharikid 10-18-2010 02:40 PM

I had the same problem with my SL30. Vans gauges and the LED indicators for flaps and trim went crazy when I transmitted. Two things changed - I moved the plane to the airport (and out of the garage) and painted it. One or the other or both are the only factors that changed and the problem went away. I also spent many hours checking grounds etc. to no avail.

breister 10-18-2010 03:39 PM

Getting more esoteric / specific with the grounds - check the following:

- Do the two COMMs ground to the same spot that the EMS does?
- Have you tested
- for zero resistance between the EMS and the Comms?
- for zero resistance between the common avionics ground point and the block?
- for zero resistance between the common avionics ground point and the battery?
- for zero resistance between the battery and block?

I bought an older (relatively) plane not well cared for. All of the above had problems; even the battery cable / power cable connector crimps were not tight (absolutely not obvious unless you yank on them - then they come loose).

Many people's Garmins sit right next to their Dynons with no trouble - I don't think it is RF transmitted by the antenna.

RV7Guy 10-18-2010 03:50 PM

My neighbor just had this same problem with his new RV last week. Similar equipment but the EFIS is Advanced flight. I believe he used a Ferrite donut to solve the problem. I'll call and check with him. He's not on the list.

Ironflight 10-18-2010 04:13 PM


Originally Posted by breister (Post 477135)
Many people's Garmins sit right next to their Dynons with no trouble ....

But do they sit right next to their Dynon Skyviews? Two different generations of equipment - one with tens of thousands of hours of flight time, and another that is fairly new in the air.

elippse 10-18-2010 04:36 PM

As I understand this problem, you have sensor cables that pass through the firewall into the engine compartment and these wires are getting EMI when you transmit, true? If that is the case then I would consider that the transmit power is passing through your compost cowling and is being picked up by the wires, which then pass it into the box where the circuitry rectifies the radio wave, a typical scenario. To get rid of this, you must place series impedance with the wires and shunt impedance across the wires. The solution, if this is the case, is to either connect chokes in series with the wires, or small ferrite beads over them, or a large ferrite over the cable, and small capacitors across each signal to the return. 0.001uf, ceramic disc capacitors with very short leads, will do the job if the chokes don't get rid of all of it.

marchudson 10-18-2010 05:00 PM

The latest that I have tried
Roger - I initially made the mistake of checking the system indoors but quickly learned my lesson on that one. All test have been made with the AC parked at least 50' from the nearest building.

Paul - Initially I did contact Dynon to see if anyone else had this problem or not. They indicated that I was the only one to report such a problem so I decided to double check variables and components one at a time to make sure I didn't make a mistake on the install.

In an effort to isolate systems as much as possible, I removed the SL-40 from the aircraft and fabricated an additional 15 pin cable for it. Grabbed a store bought RG-58 coax cable. Then removed one of the RAMI bent whip antennas from the aircraft. RAMI instructions say that the antenna needs a 24 square inch ground plane. I had a spare sheet of 24 X 24 aluminum that I attached the antenna. Checked that the antenna was properly grounded to the mounted piece and that the center conductor was not shorted to ground. Rolled the aircraft away from any buildings. Connected the SL-40 to a spare 12V battery I had and fired it up. To be clear, a 12V battery, RG-58 coax, RAMI mounted to a piece of 24X24 aluminum, and a switch for keying the mic. The basics for a portable comm. Nothing connected to the aircraft whatsoever.

The only thing powered in the aircraft was the Dynon Skyview via it's battery backup. I had disconnected the ADHARS so the only thing connected to the Dynon was the EMS. Transmit on 118.0 while holding the antenna in different locations. When held below the aircraft simulating it being mounted to the belly but NOT touching the aircraft, EGT/CHT jumps from 80deg to 120-130deg. It is worse when the antenna is held above the aircraft. Laid the antenna on a pillow thinking that my body would affect wave propagation. Still get the EGT/CHT random spikes when transmitting.

I received the EMI/RFI ferrite coils from MGK electronics. Tried them on multiple location with zero effect. I actually expected some difference with these.

Mel graciously said that I could use his SWR meter. Going to pick it up tomorrow. I'm thinking it can only be one of two things. Either the antennas or the EMS unit itself.

I'm waiting on a return call from Dynon to see what they have to say.

I appreciate all the great input and support.

KRviator 10-18-2010 05:31 PM

marchudson, you've said when you disconnect the sensor inputs to the EMS, the problem goes away.

It's likely to be a PITA, but have you considered disconnecting them all individually, then reconnecting them one at a time to isolate which one(s) give you the strange readings? At least then you can concentrate on CHT4 or your Tach input or whatever it is that is causing the problem directly.

Another suggestion would be to verify zero resistance between all 6 ground pins on the DB37 EMS Module plug and the ground point. Something I've also noticed in the SkyView installation documentation, Table 15 specifies Pin30 as a ground, but the tables for various engine examples show it as "not connected". No idea if this could cause your issues but it might be something to raise when you're on the blower with Dynon.

scsmith 10-18-2010 08:36 PM

Dynon thermocouple bundle connector?
So, now I'm wondering if it is in the connector on the back of the EMS where all the thermocouples plug in. On my Dynon, EMS-D120, that cable was made by Stein, I think, and it works fine.

Your hand-held radio test, your probes dangling test, and your SL-40 off the airplane test, all suggest that RFI is getting into the thermocouple signals, not antenna or airframe grounds. Since we all use thermocouple wire that is unshielded and we don't have problems, its not the wires. So I'm wondering if there is something in the connector - maybe bad grounds, or maybe the thermocouple leads are grounded wrong at the "cold junction" inside the box or at the connector, or something like that.

Based on everything you've tested, I would conclude that it is a Dynon problem, and ask them to check it out.

Tell us what the antenna signal testor says.....but that seems like low probabily given that it is a production antenna.

This is a strange one, to be sure.

breister 10-20-2010 08:48 AM


Originally Posted by Ironflight (Post 477147)
But do they sit right next to their Dynon Skyviews? Two different generations of equipment - one with tens of thousands of hours of flight time, and another that is fairly new in the air.

Don't really know for sure - that might best be a question posed on the Dynon forum. Certainly that is one of the things all these forums are for - to to share experiences and find out if there are trends among certain pieces of equipment.

Given that it happens with BOTH radios I am not convinced that it is an RF problem (both units generating significant noise?). But that's just Occam's Razor and I'm not an electronics guy. I only know that in my installation (not the same as the OP) 95% of my problems were grounds. One other problem was indeed related to a piece of equipment - I was one of the 10% who had problems with my TruTrak AP until I installed the $15 in-line filter. There is a sticky on their site about that problem - don't know if it would be practical to try that experiment with an EFIS; certainly not on the connector feeding EGT/CGT, but perhaps on the power/signal connector it might help.

Sunriver Ken 11-24-2010 10:01 AM

So where did this thread end up?

I have the same type RFI problem with the ammeter gauge but I am confident it is casued by the #2 Comm as the #1 comm does not create a problem and it runs to the left of the pilot while the coax for #2(the culprit) runs to the right of the passenger. The ammeter sits on the right side of the panel.

Can any damage be done by this high RF spike? If not I can live with it as this is a flying airplane with a slider canopy and it is tough getting under the panel.

marchudson 11-25-2010 07:47 AM


I finally fixed the problem. I'm out of town now for Thanksgiving but when I get back, I'll post results with pictures.

marchudson 12-01-2010 03:01 PM

Finally Fixed problem
After numerous contacts with Dynon, my system for some reason was picking up RFI from the CHT, EGT, AMP sensors and feeding it to the EMS module. The EMS module was not filtering it out and this noise was very noticeable on the gauges.

A very few, less than 5%, of Skyview customers had reported problems with the main panel emitting RFI and were noticing it on the radio. Dynon's solution was capacitive filter from this company. and the people that used these filters reported good results.

After looking at the specs for the filters, I figured they would be an elegant solution. I went with the Capacitive filters. I had already tried ferrite coils with no luck.

Now that these are installed, I don't get even the slightest hint of noise from the EMS module even while transmitting inside my metal building. I installed the filters on all three connectors.

I hope this helps anyone that might be having similar problems.

DBone 12-09-2010 09:43 PM

different system, same solution
I want to add a HUGE +1 to this thread. I have a GRT HX with dual AHRS that was having the same trouble as Marc described, only it was showing as an altitude jump when I keyed the mic. Multiple calls to GRT and getting advice from everybody that would listen didn't fix the problem. $30 for 2 of these L-Com filters, and my world is right again. And no, I don't work for them. I'm just a super satisfied customer.

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