Rotor and Engine Tach. Noise?

[BadAir Express]

I'm having a strange noise coming through my comm. radio. When I disconnected my two stock RAF gauges (rotor and engine tach.) the noise stops. I was wondering if anyone else had troubles and if so what did you do to fix it? Is there a repair center for the RAF gauges?

 

[Harry_S.]

Have not heard of that problem before.

I'm no radioman but may be a problem with circuit routing; together or too close?!


Cheers

 

[helipaddy]

is it on all frequencies of the comm radio?

 

[reelmule]

If gauges are working the problem is most likely as Harry indicated. Adding shielding and grounding to the frame for both instruments may solve the problem. Your comm antt should be shielded.

 

[Sheldon]

Add to the shielding noise reduction such as a bad cap on the ignition system... Ham radio operator and I have chased a lot of ignition noise over the years and that little puppy has been guilty more than once, N the tac just could be helping to transmit it into the cockpit.... BTY they also use them on the alternator too...

 

[WHY]

Hi BadAir Express

When you disconnect the guages do you disconnect them at the guage or at the engine/tach source. If you disconnect them at the guage and this cures the problem then I am lost but if you disconnect them at the source and this cures the problem, then it is for sure the wiring is acting like a antenna and radiating the interference. If this is the problem then what ever cure you use will have to be installed at the source and not at the guage ( not much point trying to kill it after it has already been radiated).

Your ham friend will probably know all about the various methods such as ferrite beads, inline rf chokes and the .oo1 bypass capacitors plus the standard shielded wire.

Tony

 

[BadAir Express]

I appreciate all the responces. Let me add more info... It is on all freq. on the radio. If I turn the squelch up, it only shows up on .05 of all freq. between 118. and 136. When I've done the test, the engine is off. I have a switch that cuts the power wire. Thats the one I've switched off and the noise goes away. I did not shield the power or ground to those guages, however the signal wire from the sending unit and the computer is both shielded. Also my tach's are located one on top of the other and the radio is to thier right. (about 1/2 inch away.) Keep comming with the suggestions, PLEASE!!! Im hopefull!

Thanks Curt

 

[fiveboy]

Might this help?

Might this help?

10,000uF Electrolytic Capacitor
This 10,000uF electrolytic capacitor is an inexpensive and useful addition to your aircraft’s power supply. It can significantly reduce noise signals on your power supply that may be affecting your VHF radio, such as ignition noise or rectifier/regulator noise artifacts.

Note: The capacitor must be installed as close as possible to the noise source, in parallel (across the + and - of the power supply going to the noise source), with very short leads for maximum effect.

Price: $6.50 + shipping from CA

Its the very last item on this page

http://www.mglavionics.com/html/infinity_singles.html

 

[PW_Plack]

If it's strongest on certain frequency multiples, and happens with the engine and its computer stopped, it's probably broadband harmonics of digital clocking pulses generated within the tachs. It might be aggravated by a ground loop. (Yes - you can have too many grounds!)

I've ridden in one other RAF that seemed to have this issue, and the guy just put up with it, so maybe it's common, and just gets ignored by many builders who use their radios only close to airports.

Time to take the tach out of its plastic case and get some aerosol nickel coating for the inside of the plastic? Hmmm...

 

[BadAir Express]

I really appreciate all the suggestions. I will try them all one at a time until I succed. Paul, what did you mean by having to many grounds? and Where do I get this coating spray? And can you take those gauges apart if I need to go to that? Lots of questions; and even more excitement if we are successful.

Thanks all.
Curt

 

[Harry_S.]

I don't know as this will help but, I have never had a bit of noise or static in my radio. In fact, in air to air and air to ground comms. with my machine, The "loud and clear" comment was the answer to my question regarding my transmissions.

I use an ICOM handheld that is mounted apart from the MIP. I have the AAE dipold antenna connected by CX cable to the ICOM. The Sigtronics Intercom is mounted on the aft. cabin wall. The mic cable goes thru the Intercom to the radio. The only items close to the other AC wiring is the power wiring from the breakers to the radio and the intercom.


Cheers

 

[Walter]

Ground loops

Ground loops

Curt,

Grounding should be done with respect to only one point. This means a "star-like" grounding scheme, since all grounding happens at one point. It also means that there should be no "ground loop", since this means something connected to ground at two points, e.g., a shielding connected to ground at the two ends. Every ground loop forms a coil, which will pick-up radio-magnetic energy.

 

[BadAir Express]

I work out of town each week. I can't wait to get back Thursday and try some of the suggestions. I appreciate all of your comments. I'll let you know which one does the trick.

Enjoy the good air! Whip the BadAir into a good flight!
Curt

 

[BadAir Express]

To All.

I tried some of the suggestions. Ferrite beads, eleminating the multiple ground. No luck. I took the back of the gauges off. There is a circut board that is glued into the plastic case. The case is not coated with anything. In talking with some of the local folks, they seamed to think these were so-so gauges and suggested in some upgrades.

I'm intrested in learning about 10,000uF Electrolytic Capacitor. Tell me more.

Thanks again for all the help.

Curt

 

[PW_Plack]

Curt,

The 10,000 uF capacitor is a recommendation which appears to have originated with Xcom for use in the power supply leads to their aircraft transceiver. (See connection diagram here.) The purpose is to protect the radio from voltage spikes which are produced by some alternators and other electrical accessories.

It's not likely to solve your problem, unless the path for the noise reaching the radio is through the power leads. Test this by temporarily powering the gauges from a separate, external 12V power supply or batteries, and see if the noise is gone. (8 AA batteries in series produce 12V, and Radio Shack should have a holder.)

The size of the capacitor required is inversely related to the frequency to be suppressed. Xcom is trying to keep very low-frequency spikes out of the radio. You're trying to keep VHF radio frequencies from escaping the gauges, so your application would require a relatively tiny capacitor. Something along the lines of a .01 uF, directly across the + and - leads right at the back of the gauges, would be plenty big enough, and you might be able to solder them directly to the PC boards inside the cases and still get it shut.

Putting a microprocessor-based gauge in unshielded plastic is poor design practice, especially for use near radios. If replacing them with better-designed instruments is an option, I'd do it.

Any chance you could bring the gauges separately to the meeting next weekend? If so, I'll bring a few things to try.

 

[BadAir Express]

This is a heck of a time to be up. Pushing 50, have to pee, thinking about those stupid gauges and the noise. I'm ready to chuck them. I wouldn't mind upgrading them. I would then have a flawless machine! (O.K. still working the bugs out of the fuel gauge too.) But other than that, My dream is near perfection. I've learned once more, that the field of electronics is just ONE MORE subject that someday I might have the oppertunity to learn. Until then, I'm glad for people like you all!

Any thoughts on a good Rotor and Engine Tach that will work with my existing rotor pickup?

Finially Making Progress with a smile on my face!!!

Curt

 

[BadAir Express]

Sorry Paul, I forgot to add, " Yes, I'll try to bring them with me to our meeting."

 

[PW_Plack]

I hear ya. I've pushed 50 clean over the edge and stood there long enough to watch it fall to a Wiley-Coyote-like *- poof -* !