Radio noise on Microair M760

[kobusf]

Flying a Jabiru with Microair M760 radio.

The past few flights I started to notice inconsistent radio behaviour. When transmitting, RPM drops. Usually on the ground everything sounds perfect, however when flying and transmitting others struggle to hear me. I also notice that my own voice in the headset is extremely loud, much louder than the normal intercom speech.

I can't understand why it is behaving like this in flight - perhaps noise levels? But then why all of a sudden now? Antenna perhaps faulty and therefore transmission distorted?

I noticed the RPM drop a few months ago, but then noise levels was no issue. I therefore think the 2 might be unrelated.

I am really buffled with this ons and any help would be appreciated.

[weedy]

I have found the Micorair does not like low voltage, and becomes noisy if it does'nt get its 13+ volts. But as u say it might be an aerial issue, broken shielding?
I have recently install a nice fat 22uf Cap which made a big difference (Rotax 914).

Let us know what you find.

[kobusf]

Thank you for the feedback Weedy

Where did you install the CAP?

[weedy]

At the voltage regulator, on the + feeding the battery and to earth.

And it 22,000uf

[ZULU1]

Just make sure its about a 63 Volt cap or more.. dont like smoke in aeries...

Ciao Paul

[kobusf]

Thank you Paul and Weedy.

Will try over week-end.

Paul, just want to ask, if I need to adjust on the radio, does this sound like the Tone or Power Output that needs adjustment?
I presume the problem is too much power as the RPM drops. My assumption is that the high output interfears with RPM meter.

The thing that does bothers me is that this only happens at higher speed with more cockpit noise. Normal idle and taxying is perfect.

[Boer]

Also make sure that your antenna cable doesn't run close to anything that carries voltage - the insulation on your antenna cable might have scuffed through and now a bit of voltage might be influencing your transmission.

[kobusf]

Thank you Boer

[coastwise]

I had radio and rev counter problems at one stage, where the rpm indication dropped whenever I transmitted on the radio. Found corroded and loose ground connections. cleaned and tightened and that was the end of the problem. Bad earthing can cause all sorts of nonsence.

[kobusf]

Thank you Coastwise and everyone else. This all being extremely helpful.