KELPkid
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Posts: 5247
Joined: Wed Nov 02, 2005 5:33 am

Where's The 400 HZ "hum"?

Thu Feb 23, 2006 6:19 am

Hi,

anyone remember the not-so-distant past, where in-flight PA announcements and airliner radio transmissions often featured the familiar 400 Hz "hum" in the background? (presumably from the 400 HZ AC electrical bus...).

Either I'm going deaf at the 400 Hz level, or this once familiar airline aviation sound has disappeared? (presumably due to better electronic filtration...)

Anyone know the answer?

Thanks!
Celebrating the birth of KELPkidJR on August 5, 2009 :-)
 
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Starlionblue
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Joined: Fri Feb 27, 2004 9:54 pm

RE: Where's The 400 HZ "hum"?

Thu Feb 23, 2006 6:48 am

Quoting KELPkid (Thread starter):
Either I'm going deaf at the 400 Hz level, or this once familiar airline aviation sound has disappeared? (presumably due to better electronic filtration...)

I think you answered your own question there  Wink
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
timz
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Joined: Fri Sep 17, 1999 7:43 am

RE: Where's The 400 HZ "hum"?

Thu Feb 23, 2006 7:54 am

I just heard it a couple days ago-- some sort of WN 737 I think it was.
 
prebennorholm
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RE: Where's The 400 HZ "hum"?

Thu Feb 23, 2006 8:00 am

If someone has a cure, then please come here and repair SAS's MD'80's.

After 25 years of 400 Hz hum it would be nice to hear what they want to tell us before take-off and landing.

I used to assume that they want to tell roughly the same thing as they tell on their Airbusses.

I always wondered how a plane can be certified for flight with such a lausy PA system. What if there was something important to tell the pax?
Always keep your number of landings equal to your number of take-offs
 
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Starlionblue
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RE: Where's The 400 HZ "hum"?

Thu Feb 23, 2006 8:51 am

Quoting Prebennorholm (Reply 3):

I always wondered how a plane can be certified for flight with such a lausy PA system. What if there was something important to tell the pax?

Yell. Incomprehensible but you can try to get your point across with volume.  Wink
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Buzz
Posts: 694
Joined: Sun Nov 21, 1999 11:44 pm

RE: Where's The 400 HZ "hum"?

Thu Feb 23, 2006 10:23 am

Hi KelpKid, Buzz here. Maybe i'm going deaf also.... i don't hear it so much.
Lst time i really noticed it was when i was wearing a headset and let the dangling cord get close to the External Power cord, it transmitted reasonably well into the headset.
g'nite
 
sccutler
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RE: Where's The 400 HZ "hum"?

Thu Feb 23, 2006 12:10 pm

...I always figured that, when I fly in some of the airspace known for being more "hostile" (ORD Approach comes to mind), I could improve the quality of service if I had a tone generator overlaying a slight 400hz on my audio when transmitting.

I could be the first Bonanza with a 400hz AC bus, and CSD!
...three miles from BRONS, clear for the ILS one five approach...
 
MX757
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RE: Where's The 400 HZ "hum"?

Fri Feb 24, 2006 4:56 am

Quoting Starlionblue (Reply 1):
Quoting KELPkid (Thread starter):
Either I'm going deaf at the 400 Hz level, or this once familiar airline aviation sound has disappeared? (presumably due to better electronic filtration...)

I think you answered your own question there

He did. Most new aircraft have better filtering (Shielding) then older ones.

Here is something a little off subject. If you take a multi-meter into an E&E bay of an aircraft, powered up of course, and set it on Hz you will pick 400 Hz with the leads hanging in free air. The 757 is the best to do it in.
Is it broke...? Yeah I'll fix it.
 
cancidas
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RE: Where's The 400 HZ "hum"?

Fri Feb 24, 2006 11:55 am

when you plug in 400hzand a ground comm headset you're nearly microwaving your brian....
"...cannot the kingdom of salvation take me home."
 
A/c train
Posts: 674
Joined: Sun Jun 10, 2001 7:57 am

RE: Where's The 400 HZ "hum"?

Fri Feb 24, 2006 9:14 pm

improved cable screening, radio filters and checking static wicks is what rids radio interference.

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