Antenna terminations, chasing the hum, and baffles

It seems that finding time to work in the shop is difficult this time of year. But today, Eric and I were able to spend the majority of the day working on things. Eric got all but one of the antenna BNC connectors crimped on. We need to order one more BNC connector and we will have all the antennas done.

We also spent a little bit of time troubleshooting the humming that is coming through the intercom. Eric correctly surmised it must be coming from the EFIS system. I think he figured that out because the humming will stop for about 1.5 seconds when a radio source receives. The only channel on the audio panel that will mute when a higher priority audio source comes through is the music input. When Stein wired the audio panel, they used the music input for the audio warning from the EFIS. So with that knowledge we pulled the circuit breaker on the MFD EFIS screen, and low and behold the hum went away.

So we went digging into the MFD connector. We were going to pull the audio pins out to see if we could isolate the source of the hum to the screen itself or some kind of ground loop or induced current in the wiring. Unfortunately we didn’t have the correct pin extractor.

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So we swapped the PFD/MFD screens and the hum became significantly less. We want to do more troubleshooting and ask Garmin and Stein about this, but Eric is leaning toward the actual screen generating the noise. With the screens swapped, the hum is only minimally annoying, and won’t be a show stopper, but we would still like to eliminate it completely. So we will see what we can find out.

While Eric was working on these things, I was working more on making serial number 3 of the baffle system. I cut, fit, bent, and located holes for the horizontal “shelf” pieces of the aft baffle. Everything fits together decently for a pieced together system. I still long for less pieces, and less seams. But the pieces get significantly complicated trying to do this. By making more smaller pieces, I don’t have as much wasted work if I have to make changes. A multiple piece system is certainly going to do the job, but isn’t as elegant as I would usually look to do.

My plan is to get this multi-piece system working, and verify that everything cools properly. Then, after the airplane is flying and we know the cooling works well (and I have time), I will work on making a more elegant, fewer piece system. Next is to secure the pieces to each other and add nut plates. Then we will clean up edges and move on to the baffle seal.

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