RFI

[Guest DonC]

Anyone with a J 230 and Becker coms having ignition interference problems? Mine transmit ok but any station over about 30 nm is drowned out by the noise.

 

Tried ferrite beads , shielding , etc , etc.

 

 

[Wilfred]

This is a bit of a problem both here and overseas and is not confined to the comms but seems to be more related to composite aircraft and the lack of a ground plane.

 

Looking at US web sites there are a lot of tips as to things that have been tried with most effective seems to be as detailed below

 

The only radio frequency interference (RFI) problem unique to the Jabiru engines is the result of their choice of a single phase permanent magnet (PM) alternator. It's a good alternator, but three phase is better. When they had trouble with the original system they chucked the better (IMHO) three phase PM ALT and derated to a single phase system. The result is that instead of <1.5 volts DC peak-to-peak ripple current (as dictated by RTCA DO-160) it has a whopping 14 volt ripple! This generates lots of RFI for us Jab drivers to deal with.

 

Fortunately, the fix is simple and cheap. Simply install a computer-grade electrolytic capacitor in thesystem just downstream of the voltage regulator (VR) and you now have a 1.5 VDC or less pk-pk ripple and lots of noises go away! My VR output leads both go to the (+) terminal of the capacitor (filter,

 

suppressor, whatever you want to call it) and then on to the the BAT via an overvoltage protection relay. You can go directly to the battery if you don't have OV protection. It doesn't matter. The (-) post of the capacitor goes to ground.

 

"Computer Grade" capacitors are used because they have machine screw posts to which a ring terminal connection can easily and reliably be secured. They are polar, ie they have a (+) and (-) side, and you don't want to cross them up or you make get a gooey mess where the Capacitor used to be :o)

 

Boyd May wrote:

 

I am a Jabiru J200-400 builder in Australia and have found that a ferrit rings fitted on the kill switch wires and to the main power cable to the Bus Bar are of a help.

 

Some owners have used the NGK DR9EIX Iridium plugs but the factory says not to as they can cause the coils to fail over time We have not done any of the above mods but have gone over all the earths, and, when using the radio when you know you need good power, turn the strobe off.

 

We took our Jab to a guy at Archerfield who also recommended checking the earths very carefully especially the choke , carby heat and throttle cable outers as if they are not earthed they can act as an aerial for the RFI . This made a slight difference.

 

Ii would be interested to hear what any other owners have to say.

 

By the way we use microair comms.

 

 

[Ultralights]

one thing i have always wondered about these new composite aircraft, is, are they primed with a electroconductive paint? all millitary and airliner aircraft composite components, (most of the F18 is composite outer fusealage) are painted in a black conductive paint, it helps restor or keep radio quality and prevent damage in the event of lightning strike as well as electrically bonds the entire airframe.

 

Would such a coating on composite recreational aircraft improve radio quality by providing said ground plane equivelent??

 

 

[Wilfred]

I would not think so for most aircraft.

 

Jab constuction seems just like building a fibreglass boat.

 

 

[Guest Fred Bear]

Interesting comment about the Iridiums as Don at Jabiru engines recommends them and uses them in his own aircraft too.

 

Not recommended for certified aircraft however.

 

 

[Wilfred]

Jabiru specifically advise not to use resistor plugs with their ignition coils. I recently wrote to them on this subject and had this re-confirmed.

 

I was also told that there have been quite a number of coil failures in the states and ST aviation also advises not to use them.

 

if you have any correspondance from Jabiru that is different please post it.

 

 

[Ross]

Hi All

 

I have a tail mounted strobe on my J160 not flying yet and it was interfering with the radio until I shifted the shielded strobe wire to run along the side of the fuselage cone instead of parallel and near the shielded aerial wire which runs up the bottom middle of the fuselage.

 

The two wires do cross in the aft end of the fuselage.

 

I think the strobe power box is made of Aluminium so it may also be a source of interference.

 

The J160 has a dipole aerial. Hence itdoes not require a ground plane.

 

The space between the two pieces of the aerial is critical so I made up a spacer that I placed there until the epoxy holding the aerial in place set.

 

Fibreglass gliders usually have their dipole aerials buried inside the vertical stabiliser but may also have a RFC (radio frequency choke) connecting the two halves in the tail. This allows the aerial to be tested for continuity at the cockpit end with an ohmeter - not a 12 volt battery. (radio shouldbe disconnected from aerial while testing with ohmeter)

 

You do not need the RFC for the aerial to work.

 

The RFCpasses electric current but not radio signals, hence its name.

 

It is only in the circuit so that an ohmeter can be used to test the continuity and resistance of the aerial circuit from cockpit to aerial and back. Over time the resistance should be constant. If it changed the aerial wire is broken or there is a short circuit in the wiring.

 

The J160 kit does not include a RFC for its dipole aerial so cannot be tested for continuity from the cockpit end easily.

 

To do soyou need run an extra temporary wire outside while you are doing the test to connect the other end of each half of the aerial as you test it.

 

The initial test w/o the external connection should show open circuit between inner and outer aerial wires if no RFC is fitted. If you want to fit a RFC find a radioexpert - I am not one.

 

Ground all wires to remove any static charges before reconnecting the aerial to the radio.

 

I am a bit worried about my undercoat paint as it appears to be mildly magnetic (and conductive???) as it picks up on amagnet from the floor after rubbing back but that could be from the abrasive paper used.

 

Might it therefore interfere with radio reception and transmission.

 

Paint is High Fill Imron brand.

 

Any Comments please.

 

Regards

 

Ross

 

 

[Guest danda]

I hope this isn'ta dumb question, However because of composite nature of the aircraft and as it pushes through the air could the body of the aircraft be producing a static charge causing some of the interference?

 

I was thinking back when I was a kid how you would rub a plastic ruler on your shirt and creating static chargeenabling you to pick up a peice of paperjust a thought.

 

Don