6300 microphone audio interference

Paul Burton

I have been off the air for about one year and when I recently powered up my Flex 6300 everything seems to be working normally except that there is a motorboating sound in my microphone audio (front panel input with a dynamic mike). It has a regular scuffing sound and a background scratching sound. If I unplug the microphone it goes away. CW and digital modes work fine. The interference is there with the RF power at zero, so it's not RF getting into the audio. I'm suspecting a bad A/D converter in the audio input. Anyone have any ideals on this?

Thanks, Paul

Paul Burton

The mike level indicator is jumping around, even when I'm in receive mode, so I don't see RF getting into the mike.

Paul Burton

OK, I disassembled the mike connector again and found a marginal connection on the shield grounding. After fixing this problem the noise has now gone away. So the problem seems to be solved. Thanks for your help.

Paul - AA6Z

John KB4DU

Is the mike active, like mox on, or vox on? What audio setting are you using in SmartSDR?

Paul Burton

Thanks for answering John. Yes, the mike is active. My voice comes through but is accompanied by the interfering sound. I am using MOX to key up the audio (have never used VOX. I'm not sure what you are asking about the audio setting. I have a mike plugged in the front panel. DAX is off. If I enable the level meter on receive, the interfering sound is showing on the level meter.

James Del Principe

Paul, check grounds on the mic. May not be secure. Then, try another mic. Borrow one if you must.

Mike-VA3MW

Please post a screen shot of SmartSDR while this is happening.

Paul Burton

Thanks for the replies. I checked for continuity and shorts on the mike cable and it was ok. I disassembled the mike connector to the rig and the cable was wired to the proper pins with ground. I tried a second mike (similar to the first one) and it exhibited the same behavior. Here is a screen shot of SSDR while it's happening. Note the -30 dB level (which is jumping around).

WX7Y

Just looks to me like your Downward Expander is not on or not set correctly.

Paul Burton

OK, thanks for all the comments on this problem. I suspected the mike cord, so I totally rewired it and found that the ground connection was faulty. After correcting this, it is now working with no interference. I am not using the Downward Expander, but will look into it.

Thanks to all for the help.

Paul - AA6Z

John KB4DU

Unrelated, but I suggest revising the transmit EQ settings for two reasons.

Depending on how your transmit bandwidth is set the boost at 4K and 8k is boosting frequencies that are probably well outside that bandwidth. This can cause clipping and distortion in the transmitted audio. Since the mic level meter is before the eq it may be showing a level below the actual level applied for modulation.

Second, the general rule is to cut before boost. If all the EQ sliders were lowered by the same amount, the curve would be the same with a more accurate level meter indication.

Paul Burton

OK, John. Yes, I have been off the air for a year, and that setting is obviously wrong. I get good audio reports, so didn't really look at the transmit equalization. Thanks for the heads-up.

Paul