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Bosse

Saturated Audio Amplifier causes interefence.

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Hello everyone.

I use an electrec-microphone to record audio from my airplane. It works very well generally.

However, since I think it is fun to record turbulence sounds, servo buzzing, funny comments from bystanders and the microphone output is too weak for that, I decided to install a microphone amplifier. That works great as long as the engine is not running or idling (a glow engine).

When engine runs at higher revs, i get video-interference. I guess it is due to either signal level is too high on TX input, or OP-Amp on amplifier board acts up somehow and causes interference. I have adjusted the amplifier to minimum amplification with some success, but then im back where I started.

I guess I need AGC on the audio amplifier.

Has anyone had this problem and how did you cope with it ?

Best Regards,

Bosse

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Your complaint is somewhat common on nitro models. Even my e-powered Soarstar suffered from video image noise due to the over-driven audio subcarrier. I had to hack the audio preamp to tame it. The usual symptom is horizontal lines in the image that change intensity as the model's RPM changes.

One fix is to damp the engine noise and vibration, at the mic, with foam. If that does not help, then you will have to devise a way to attenuate it electronically at the audio input of the Tx.

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Thanks for your reply.

As it is now, the microphone is located inside the fuselage. I think I will install it somewhere outside, far away from engine, with some foam around it, and point away from airframe..

I might also change the feed-back resistor on the audio-amplifier to lower the gain more than is possible by adjusting the trim-pot.

Best Regards,

Bosse

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