Strange Radio? Interference?

[old man emu]

6 hours ago, cscotthendry said:

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

I think someone has dropped himself in!

[cscotthendry]

6 hours ago, RFguy said:

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

 

 

 

 

What about having the iPad within 1 meter of the radio itself. This is the case in just about every cockpit out there.

And yes, I know the radio case is a Faraday shield but I've had this issue on 2 airplanes I've owned so far, 1 home built and one factory.

BTW, I'm an ex USAF avionics tech and I know that RF is like water. It can get into some strange places.

[spacesailor]

SQUELCH,.

The sound of mud between your toes.

The sound of Water in your wellies. LoL

 spacesailor

[RFguy]

Ipads dont emit much energy.  radios are well shielded but they are not completely  'air tight'. the metalwork has gaps.

however radios also have antennas.....

The pickup of an antenna is approx 10,000,000 (yes ,real numbers)   times more sensitive than  energy getting in the gaps.

 

There are two main ways noise gets into aircraft radios

 

1) direct pickup- the antenna can pickup the radiated noise.. IE the radiated noise from a device has enough energy to reach the antenna  and be greater than other noises. Antenna placement AWAY from the cockpit is the real solution here. 

 

2) RF rubbish from the IPAD etc, nearly co-located with the radio, gets onto the outside of the shield of the coaxial cable (closeby) , travels up to the antenna, and, if not well grounded, shielded (which is all a compormise in ANY small airplane) , will 'fold around' and come back to the radio on the 'inside' of the shield.   

 

The RF rubbish from the IPAD- USB charger etc can also travell along its own power lead - the power lead becomes the antenna. 

 

If it is a composite aircraft, its highly likely RF garbage is getting onto the cable and it folds around at the antenna.

 

Also, noise and interference form the cockpit and get onto control cables  , other power wires etc and carry the noise up to the back of the aircraft where your antenna is.

 

 

 

 

 

[Jabiru7252]

Interference can also get in via the power lead to your radio.

[walrus]

Got a multimeter on the engine today..... The engine airbox and throttle body assembly is NOT grounded to the engine block. I don't know if this is by accident or design.

 

The central throttle wire core inside its teflon sleeve, and throttle spindle is not grounded either.

 

 When I touch the throttle spindle, I get ignition/computer noise in my noise cancelling Bose headset,, but not if noise cancelling is turned off.

 

My ignorant speculation is that the throttle wire is radiating RF noise enough for the headset electronics to be affected.

 

I assume at this stage that if  I ground the throttle wire/airbox assembly, the noise will stop, but I want to check with rotax first since the 912iS has two completely separate electrical systems with their own isolated grounds...

[RFguy]

I think It would be isolated from ground by accident. I'd ground it. just a strap over to the block.

[walrus]

Grounding the Airbox stopped the noise.

[RFguy]

excellent.

I will check mine . I would expect isolated, also.  Best be grounded.

 

If other planes have same setup, and don't have the noise troubles, probably points to some other problem, yet unknown.

How well is the engine block bonded to the firewall ? Only path would be probably :

- oil sender return,  ignition  mag grounding, chopped up alternator stator signal. 

 

- IE nothing direct- Only indirectly. I'd like to see an inch wide copper phospher bronze  strap from block to firewall.

 

 

[cscotthendry]

4 hours ago, walrus said:

Grounding the Airbox stopped the noise.

Fantastic!

Thanks for the update.

[walrus]

-2 Aircraft tefzel ground firewall to block - same as for starter +ve as solenoid is a remote separate item, not part of the rotax starter. Hydraulically crimped AN terminals. One common grounding point for the battery and block on the firewall and tied to that is an Aeroelectric (?) grounding block with about 20 spade connectors. All audio and radio are shielded and grounded one end only to that block. All terminals are amphenol diamond grip crimped.