Strange Radio? Interference?

[walrus]

I don't know where this subject belongs, so I'll try here.

 

I have Bose noise cancelling headphones connected to a Dynon intercom. I have a fuel injected Rotax 9912 iS engine.

 

Whenever I touch the metal shaft of the throttle, I get ignition noise in my headphones. Otherwise there is no noise from strobes, lights, etc. As far as I can tell everything is grounded as it  should be What is going on?

[FlyBoy1960]

Do you have a ground lead to your body when you are flying ?   

 

I would recommend around 1100 mm of braid attached to your thigh with a small screw for each flight

[walrus]

Quote

Do you have a ground lead to your body when you are flying ?   

 

I would recommend around 1100 mm of braid attached to your thigh with a small screw for each flight

 

I've tried an alligator clip to my  ear but it interferes with the headphones.

[old man emu]

Would this be a better place than the earlobe?

[walrus]

That could work but on reflection, I like a small screw now and then.

[spacesailor]

A screw in the leg ,.

Better off with a touch of Super-glue.  LoL

AND Why a New screw for each fligh.

Are you a Screw sales person ?.

Weird Grammer /spelling

screwless spacesailorr

Edited April 10, 2021 by spacesailor
A little extra

[facthunter]

Your body can  act as an aerial. Nev

[FlyBoy1960]

5 minutes ago, facthunter said:

Your body can  act as an aerial. Nev

See post 2

[facthunter]

Your body might have too much internal resistance for that to be fully effective.  Insulate the throttle knob maybe? Nev

[Jabiru7252]

7 hours ago, walrus said:

I don't know where this subject belongs, so I'll try here.

 

I have Bose noise cancelling headphones connected to a Dynon intercom. I have a fuel injected Rotax 9912 iS engine.

 

Whenever I touch the metal shaft of the throttle, I get ignition noise in my headphones. Otherwise there is no noise from strobes, lights, etc. As far as I can tell everything is grounded as it  should be What is going on?

 

Try to narrow down the problem. Occur engine off or running or both? Does it occur with a standard headset (no noise cancelling stuff)?. Does it occur both sides, pilot and passenger connections? Has anything been done to the plane that may have caused this, for instance did the problem start after your last service. And, just a personal note, if I was flying in Afghanistan I'd be worrying about a lot of other stuff rather than my headset...

[walrus]

Facts and Jab.  The noise occurs only when I touch the metal throttle shaft. The knob is insulated and there is no noise when I touch it, nor is there any noise when I touch other metalwork.

 

The noise is coming from a running engine only. On the 912 iS, the throttle cable is pretty close to the wiring loom and I suspect "crosstalk". The outer case and inner wire are grounded to the throttle body on the inlet manifold.

 

What I have not yet checked is the ground between throttle body and airframe. The 912 iS also has two electrical systems for redundancy that have separate grounds, so I am not sure if that is a contributing factor.

 

Its a nuisance more than anything, but its annoying.

[Jabiru7252]

Even though the engine is rubber mounted I would be very surprised if it wasn't electrically connected to the airframe. What happens if the throttle shaft is grounded while you're touching it and experiencing the noise?

[walrus]

Jab, Yes, I have grounded the engine block to the airframe. You raise a good question about the grounding of the throttle. I think it is grounded through attachment to the butterfly on the throttle body but I will check.

[facthunter]

You want more than an earth through rose joints or levers. It's quite possible the throttle isn't earthed adequately on that engine with the rubber connections. Nev

[RFguy]

this noise in the headphones.
is the radio turned on ?
(is the intercom integral to the radio ) ?
does it sound like ignition noise being radiated by including you as part of the incidental antenna ? varies with RPM ?
Is this a composite or full metallic airframe  ?

does it change when a heavy load is on the generator (say incandescent landing lights on)  ?

does it vary with radio or intercom volume level ?

does it vary with radio frequency (if involved)

with squlech of radio off (pure nose hissing out of radio) can the radio  hiss  character be detected to be varying when making that contact ?

 

 

[walrus]

RF, radios are on, they feed through the intercom panel.  Its not alternator noise that varies with load, metal airframe. Everything grounded and shielded, no strobe noise, etc.. Not affected by frequency or squelch. No hiss.

 

Just tapocka, tapocka, tapocka  when i touch the metal throttle shaft (not the bakelite knob)..

 

I will check grounding of the throttle body butterfly shaft. The body is attached to the airbox and that has rubber connectors to the inlet manifold, so the grounding of the airbox/throttle body may be the culprit.

 

 

How sweet it would be to go "achtung" to the little Rotax elves in the black forest and point out an issue to these superior beings. Apart from this, I can't fault the engine.

 

 

[RFguy]

hmm .

If radios are OFF do you hear the tapocka tapocka tapocka ?

 

iif yes or no, sounds to me like  ground injection.

I'd say there is some issue with the grounding/ earth returns of your intercom wiring , not being complete.

 

[walrus]

RF I'll check next week and report back. There do not seem to be any other radio or intercom issues.

[RFguy]

OK. also,  is a transponder on and being pinged (as indicated on the display) at this time ?

 

915iS. turbo injected ? is there some solenoid opening and closing periodically ?

 

while earthing the cable might fix it, for me that indicates there is some other underlying wiring issue with the intercom, most likely.

 

[cscotthendry]

I post this every time someone has radio interference issues so here goes again.

If you fly with an iPad, make sure wifi is turned off if it is not communicating with another device otherwise it will search for a connection and its transmissions will play havoc with the radio.

BTDT

[RFguy]

It's transmissions should not cause any radio interference.
" and its transmissions will play havoc with the radio."

I put an IPAD into a TEM cell and it did emit some rubbish but the radio antenna would have to be within 1 meter to cop it.

 

That sir may be your experience, but it would I would expect only be likely with a poor radio antenna installation, an installation with thee radio antenna too close .

In a composite plane, suggest 2 meter distance from electronic devices and good ground, and ferrite chokes on the cable.  without the ferrite chokes the cable wil pick up from close to the Ipad/cabin

 

 

 

 

[old man emu]

Seems that what is needed is someone with the training and experience to write up an explanation of possible sources of radio interferences and the methods one could use to eliminate interference. 

[RFguy]

would make a useful text. could be done with an enormous flowchart

[IBob]

I would support that: I hate shotgunning (just swapping/adjusting stuff piecemeal until the problem goes away). It's the lowest form of troubleshooting.

[Jabiru7252]

Half the problem is that most pilots do not have a deep understanding of radio and electronics, and many (like CBers) thinks they do. The number of times I have had to explain squelch to somebody is huge.