Radio noise

[ianboag]

I have a fairly standard J200 and MicroAir 760. Works OK - quite useable - but there's enough noise to be a pain. It's plug noise as far as I can tell - tickety-tick and not a whine. Squelch deals to it most of the time.

 

What do we know? Who has had this problem and dealt to it? Plug lead resistor inserts? Resistor plugs? Super Cheap noise reduction kits? Snake Oil?

 

All ideas gratefully considered ...

 

IB

 

 

[jcruffle]

Ian, do you have a transponder fitted as well? I have a Microair and the noise sounds similar, but it is there only if the transponder is turned on (and some days it is worse than others). Someone once suggested it is the proximity of the VHF to the transponder in the dash. Does anybody else with a factory 230 or similar have the same problem??

 

John

 

 

[Guest AusDarren]

Hi, some years ago I had plug noise affecting the radio in a car I bought.

 

It turned out the Plug leads were close to other leads that went through the firewall,

 

and that was in effect an aerial for plug noise inside the cabin.

 

To rule it out just have a look at the location of the High tension leads, and check they are not cable tied close to anything metal that penetrates the firewall.

 

The bonus is its real easy to check ;).

 

Regards,

 

AusDarren

 

 

[quentas]

I replaced the txp lead with better quality coax and it made a slight difference. I noticed the noise changes depending on where I put my right foot in the cockpit. I suspect the txp is leaking RFI into the power wires for the radio and intercom and some physical separation helps. Adding some chokes may help reduce the noise along with good quality coax and trying to keep the wires apart. That has made it all heaps quieter. Now I can actually hear transmissions on the radio clearly.

 

 

[ianboag]

It seems that a resistor in the plug circuit is considered a good idea. There are resistor inserts for the plug leads and resistor plug caps and resistor plugs. Resistor plugs seem (to me) to be a good way to do it. The standard NGK D9EA would be replaced by the DR9EA. Has anyone done this? Was it useful?

 

 

[brilin_air]

Hi all,

 

we had a similar problem with noise caused by the transponder by the position that our feet were in, it turned out to be an upgrade in the transponder that was required as microair explained that a dry solder joint was responsible inside the unit, once it was sent back and refitted, no further problems, give them a ring at microair we have found them to be terrific to talk to about noise interference, I believe that the transponder antenna has something like 200 volts passing through it when it is activated.

 

All the best

 

Brian

 

 

[Bruce Tuncks]

Hi, I've been wondering about the magneto wires, which in the Jabiru are not the shielded type. A friend who has built more than one plane was amazed that a coaxial wire was not used here, with the outer shield grounded. I wonder if anyone can comment on the possibility of this being a source of noise.

 

cheers, Bruce

 

 

[jetboy]

Brillin air - better check your feet are not glowing in the dark or getting hair on the soles....

 

Nah the transponder is around 200 watts peak, only 2 watts average. But it can put buzzy noises about if everything is not well shielded. Like cellphones its not something thats good to be too close to, nowhere near the safety levels that require the radiation suit for my work.

 

On the subject of plugs and HT leads, it appears new engines now come with inductive supression leads standard, rather than the old red carbon coated plastic ones. I replaced the reds with Bosch leads from Supercheap with good improvements. I also use DR9EA plugs now and that helps a bit too. Because all the plug leads already have resistance, do not add resistor plug caps. The R type plugs are OK, I tested for them and the HT coil is not under any extra stress as long as the gap is kept to min. limits .020"

 

Ralph

 

 

[ianboag]

Resistor plugs/leads/caps etc

 

I found this link interesting

 

Resistor spark plugs - resistor spark plug caps.

 

Rainier Lamers wrote this in 1999. He's Mr MGL - the Stratomaster instrument people. Seems you can add as much resistance as you like and the plug will still fire, although as you add more the plug becomes more likley to fail if contaminated.

 

He says that the aim of resistance in the circuit is to knock back the spark energy and hence the radiated RFI. If that's how it works, then one would think that it doesn't matter whether the resistance is in the leads, caps or plugs .....

 

IB

 

 

[jcruffle]

I found that the antenna leads for the VHF and Transponder were cable-tied together behind the dash. We separated these and ran them away from each other. We also moved the transponder to the right so that the blank was between it and the VHF. So far so good. The noise has all but gone.

 

John

 

 

[jabpilot]

I'm new to this web site so this may be way too late and thus never read, but...

 

Although I concur with the comments made so far, I believe in doing the easy, cheap things first.

 

My Microair 760 (Rel N) had too much background noise straight out of the box. Rod Stiff said "yeah, we've been telling that to Phil (Ainsworth - Microair owner) for ages". It seems that these radios are (were?) factory set with the mic gain a little too high for most powered aircraft. Understandable as gliders drivers are a big customer base for them.

 

To fix my problem I simply inserted a small, scientific style screwdriver into the mic gain pot access hole located in the side of the radio, covered by alfoil, and adjusted the pot attached to the circuit board. WARNING: This sounds simple and is for the very dextrous but BE CAREFULL. A TURN OF LESS THAN 1/16 OF A TURN MADE ALL THE DIFFERENCE. Too much will turn the mic off altogether.

 

Hope this helps.