American Airlines and the 400hz hum

[blantonl]

Why is it that every AA aircraft has the 400hz hum on their comms? Is this an MD-80 thing?

 

[scanningisfun]

Why is it that every AA aircraft has the 400hz hum on their comms? Is this an MD-80 thing?

Look at "Uses in aviation"--

Talkower supply - Wikipedia, the free encyclopedia

Also--

Where's The 400 HZ "hum"? — Tech Ops Forum | Airliners.net

"The one thing that is unique about aircraft power supplies (in general) is the use of 400 Hz as a means of minimizing size and weight. Plus you get that great 400 Hz "whine" on the radios instead of 50/60 Hz hum."



Jacob

 

[mass-man]

Try this Lindsay...

Aerospaceweb.org | Ask Us - 400 Hz Electrical Systems

 

[kma371]

I usually notice it more on United aircraft. But very good topic and good links!

 

[jhooten]

It is also in the PA audio when the Captain makes cabin announcements on the MD-80.

 

[datainmotion]

I think I hear it less today than I remember as a kid. Most likely due to better filtering for the RF and AF systems and we don't get too many antiques flying into KDEN.

 

[tylermaule1995]

Yea I always noticed that too. Even when I fly United and your plug headphones into your armrest it makes the 400hz tone. I guess I have a answer to that, I've always wondered.

 

[krokus]

Makes me think of on the aircraft carrier I was stationed on, there was a 400Hz power distribution system, in addition to the 60Hz power system.

The 400Hz transformers were much smaller, and had more of a whine to them.

 

[737mech]

Aircraft 400 noise

Not sure about MD-80's but the 737-300/500 older radios were analog type audio assesory unit style systems and later in production they switched audio integrating to a digital Remote Electronics Unit. We found out the pulse landing light system was very bad for old style systems too much noise. Most of the time noise is fixed by repairing the audio headset wires correctly. They are shielded two wire and three wire bundles that go to the headset plugs and mic plugs. Sometimes mechs forget to repair the shields and just pull it back and away. Thus introducing more noise. And by the way pilots are buying new noise defeating headsets more and more these days. Just a work around I guess? They report noise much less now with digital audio integrating and their own expensive headsets.