dirty rf from skyview...

[schristo]

it could be that i am right on the fringe of quality reception with a belly antenna, in a metal hangar, at the far end of the airport, but with the radio stack -on- atis comes through quite clearly.  the sl40 reports a signal of 50 or so and noise around 20.  it breaks the squelch setting and sounds pretty impressive.  turn on the skyview and a significant layer of noise swamps the signal... to hear it at all you have to pull the squelch and strain to hear the words though the noise... in numbers the sl40 reports noise at 130...

hours of testing...

the noise is from the screen unit... unplugging the connections to the gps antenna, the ems, and the adahrs has no effect on the rf noise.

the garmin 696 also increases the noise level but not as much... by ear perhaps half as much...

turn off all power in the hangar and the noise level is reduced somewhat in any configuration....

open the middle hangar door and the atis broadcast becomes audible with everything on.  the sl40 reports a noise level around 100.

push the plane forward a couple of feet and it gets clearer still... reported noise drops to around 80.

turn the screens off and the noise drops to 7...

after extensive testing it is pretty clear that both the garmin 696 and skyview display put out some level of rf interference.  they do not produce any noise on the intercom, with music inputs, or when transmitting, only on a radio signal coming in.

i wanted to push out of the hangar and test in the open but the weather was not cooperating.

all and all quite frustrating.

how much rf interference is expected with the skyview?  how to measure it or characterize it?

can anything be done to mitigate it?

 

[dynonsupport]

Stephen,
The SkyView does put out some RF noise, as all electronics do. We've tested it in house, and it's on the same level as a D180, which we do not receive complaints about.

Given that both the SkyView and the 696 cause you some noise increase, I'm guessing that the shield on the RF cable to your antenna isn't doing a great job. It's one thing if you have a handheld near the screen of the SkyView, but a belly antenna a few feet away on the other side of the skin of the airplane should be pretty impervious. It sounds like your radio is picking up a lot of signal from inside the plane, which is generally an indication of sub-optimal shielding in your RF path somewhere.

 

[schristo]

hmmm.... rg400 with a relatively short run tested straight from the antenna to the radio... all without any change to the signal levels or reception while handling the cable. i would anticipate some noticeable change in signal from moving the cable around if the signal noise was associated with the cable... i will experiment with the antenna and with pushing the plane out of the hangar... i suspect that it is a fringe reception issue that is highlighting the addition of any rf source... without a direct comparison to another install in a similar environment i am uncertain what to expect in reception.

 

[RudiGreyling]

Hi Stephen,

keep us posted please...I hope you get it resolved and that it is not a Skyview issue. Dirty RF is something I don't want to content with, since COM is very important in airplanes.

Regards
Rudi

 

[DjAg5dosk2]

I am very much hoping this is an anomaly. I had RF issues for years with BMA E1 G2 gold box. As it turned out grounding the CPU was critical, the BNC connector for GPS needed good ground too. I never worked it to my satisfaction.

One should be sure power wires to breakers or in common runs are not near com wires (power or RG400) too.

Best
Howard Rhodes

 

[PhantomPholly]

Most noise is caused by bad grounds, and are truly the devil's own buggers to track down.

Make absolutely certain that there is as close to zero impedance between the common electronics ground point, the antenna ground plane, the engine block, and the battery negative terminal. Test the shield ground, and make sure there is no possibility of a "ground loop" (where one end of the shield connects with a ground near /at the radio, the other end connects at/near the antenna, and those two ground points are not electrically equal).

Last but probably should be first, check out the AeroElectric Connection. Every aircraft electrical problem ever discovered (or just about) is covered in his work.

Good luck!

 

[schristo]

*update* dirty rf from skyview...

after a week of work travel i made it back to the hangar to re-evaluate the rf interference.  to assist i picked up a regulated 12volt (13.8) power source.

bottom line - my skyview unit puts out noticeable rf noise when charging the backup battery and is rf silent when running from the back up battery pack.

first i should state that i am usually more prone to hearing, and being irritated by, small unexpected noises in mechanical or electrical equipment than others that i encounter.  what i perceive as noticeable or objectionable others my not hear or recognize as bothersome.  having said that, the layer of additional rf noise initially observed could not be missed by any listener and is quantified readily by the noise signal detail from the sl40.

today i started by verifying the condition and testing various grounds and resistances associated with the signal.

for both the skyview and the garmin there is some rf noise introduced when they are charging a backup battery.  with the garmin fully charged it does not contribute any rf noise so i focused on the skyview.

to eliminate ship power issues i tested the skyview with external power and ground from a regulated source (without connection to the adahrs or ems)...  no change was observed but it did highlight a non-continuous, stepping/stuttering current load with the battery in a charge cycle.  this load variation is also seen directly by monitoring the power line in the vp-50 when supplied by ship power.

i pushed the plane out of the hangar to test in a clear environment.

a few points...

• neither the garmin or the skyview exhibit any rf when they are powered by their backup batteries.
• with the garmin backup battery fully charged there is no rf noise introduced when on ship power.
• with the backup battery drained on the skyview there is significant noise and the current flow through the skyview circuit cycles from less than an amp to over 3.5 amps, stepping and stuttering along the way.
• without a backup battery there is a noticeable but fairly minor amount of rf noise from the skyview
• with the skyview charging the backup battery, my tuned fm radio station from a portable plug in shop radio is also layered with some rf noise.

some numbers from the sl40 with the plane out of the hangar:

• atis signal strength: 70
• signal noise during atis broadcast with either or both 696 and skyview on backup battery power: 7 (this sounds close to 'studio' quality... at least for an atis broadcast)
• give the skyview ship power and the noise increases to 12-20 (this sounds like a good quality aircraft atis reception - it is good... switching to battery backup power cleans the signal to great.
• plug the backup battery in and there is noticeable increase in noise but it appears to be more pronounced with a drained battery...

normal use will be with a charged battery and i suspect that the logic for maintaining the charge with a trickle will be far less of an rf noise issue than with a drained battery.

it may be that there is some control logic that could be reviewed in how the current draw is managed when charging the battery and how this effects rf noise...

i would like to have a fully charged backup battery to represent a typical normal condition but i need to get some small pins, or something figured out, to connect it to a charger... it is too troublesome to charge it through the screen unit without the engine and alternator providing a source.

in any event i have spent too much time in this and will push on...

 

[dynonsupport]

Please DO NOT charge the battery with another charger. These are lithium ion batteries and need to be specifically controlled. They have a protection circuit built in so I guess any damage is unlikely, but no reason to tempt that.

 

[RudiGreyling]

Thanks Stephen for going the extra mile...

DynonSupport any comments on Stephen's findings? It looks like the Lithium Ion charging side of the Skyview generates some noise? Has this been specifically tested/verified during your in house tests?

Thank you in advance,
Kind Regards,
Rudi

 

[schristo]

i am not convinced that the rf noise - really degradation of the quality of the rf signal... weak signals are easily swamped... strong signals are unaffected - is exclusive to charging the battery... my testing is suggesting power management scheme, programing, or maybe i just have a bad unit?

there is something strange in how my skyview consumes power... the electrical load fluctuates significantly and continuously, more so with a battery charging.

why under a steady state is the current jumping around so much? with a charging cycle for the battery i can understand a variable current flow at times but under a steady state what is going on that requires a continuously variable current flow? it appears to be the root source of rf noise.

this weekend i tested power lines by replacing them with shielded cable with no effect.

 

[schristo]

nothing from dynon yet...

 

[dynonsupport]

Any current change you can see on a multimeter has nothing to do with RF. SkyView has lots of stuff going on inside, from loading terrain files to charging batteries that changes over time. The current draw does vary a bit, and this is expected. When charging a battery we do all sorts of fun things, and clearly we have to draw more power when charging the battery. I do expect that more RF will be emitted during battery charging. but still within the DO-160 limits.

I do believe that the fact that your 696 can cause noise shows that your radio is very sensitive to noise in the cockpit, beyond most aircraft. Clearly it is not just SkyView that causes an issue, although it may be the worst offender. The certification limits for avionics allow more energy to be emitted from equipment that is in the cockpit under the assumption that the antenna is well shielded from the inside of the plane.

If you still do believe that the SkyView is really a problem, we'd be happy to look at your unit. There are noise filters inside, and there is a chance they are damaged or degraded.

 

[schristo]

Forget any issue with the 696 there is none. All issues associated with rf noise are from the skyview. Apply power to the unit and my dewalt radio 10 feet away picks up interference, switch the power off and it is clear. In the cabin the sl40 gets hit hard with the same interference. The skyview is near silent when on backup battery power.  What is up with that?

 

[dynonsupport]

Stephen,
That sounds much worse than we would expect. We've got SkyViews all over the building and they don't mess with our FM radios at all.

I think you have already contacted us about bringing in your unit, but if that was a different customer, please contact us so we can look at your unit.

 

[RudiGreyling]

Forget any issue with the 696 there is none. All issues associated with rf noise are from the skyview. Apply power to the unit and my dewalt radio 10 feet away picks up interference, switch the power off and it is clear. In the cabin the sl40 gets hit hard with the same interference. The skyview is near silent when on backup battery power.  What us up with that?

Stephen, I hope this gets sorted soon. Like I said it looks like the charging side of the lipo battery is causing the problems.

Dynon and Stephen, Please keep us posted.

Kind Regards
Rudi

 

[RobertHamilton]

We tested Stephen's Display, and the noise emissions are within specifications and standards.  His airplane is fairly close to the factory, so we are going to track this with Stephen and determine performance as he completes his plane. We'll keep everyone posted.

-Robert
Dynon Marketing

 

[skysailor]

This dedication to customer support and producing the finest product possible at a reasonable price is the reason I will be outfitting my project with Dynon.

 

[RudiGreyling]

We tested Stephen's Display, and the noise emissions are within specifications and standards.  His airplane is fairly close to the factory, so we are going to track this with Stephen and determine performance as he completes his plane. We'll keep everyone posted.

-Robert
Dynon Marketing

Well that is good customer service.

Was it confirmed it only happens while charging the backup battery? and is quite when running on battery only power?

Keep us posted please.

Thank you in advance,
Kind Regards
Rudi

 

[schristo]

just a general update... robert provided a replacement unit but did not anticipate a different result.  i installed it this weekend and it performs similarly.

in the end i am not too concerned about the level of rf interference, while not ideal, i do not expect to be flying inside of a hangar with the engine off... with the plane pushed out the level of signal loss drops significantly.  

while there is a clear difference in interference with the unit off, powered by the battery, on without a battery, and while charging a battery... practically speaking it may not be an issue when flying.

i provided dynon with a recording from my iphone stuck inside of a headphone along with a video of the interference picked up on an fm radio with the skyview powered by a benchtop reference source to review.