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Crosstalk On UA Ch 9 On 767s?  
User currently offlineWestWing From United States of America, joined Feb 2005, 2134 posts, RR: 7
Posted (9 years 6 months 4 weeks 12 hours ago) and read 2299 times:

Hi

I am a A.net newbie and this is my first question. Please be gentle!

On UA 767s when listening to Ch. 9, there is often a very loud
background hum (possibly 400Hz interference(?)).

The hum is only present when the source is the aircraft radios (i.e.,
it is not present during a PA override announcements on Ch. 9).

I have also only heard this on 767s and am convinced it is an
not just a specific airframe.

Anyone have any explanations ? Unshielded cables between the
radios and IFE ?

Thanks



The best time to plant a tree is 40 years ago. The second best time is today.
10 replies: All unread, jump to last
 
User currently offlineSlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 1, posted (9 years 6 months 4 weeks 11 hours ago) and read 2210 times:

Welcome.

I have not heard of this before, but then I never listen to passenger entertainment systems anyway. (big fan of silence here)

Your explanation sounds plausible. I would not expect entertainment systems to be engineered and installed to the same standards as required comm radios. On channel 9 I'd expect that you are eavesdropping on the communication system rather than being an actual part of it.

Someone will pop up with the real answers to your question before long. They might also tell you to use the search function but I don't remember this being asked before.

"be gentle?"
No problem. Just don't argue with the "experts" here. (some are cranky)






Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently offlineWestWing From United States of America, joined Feb 2005, 2134 posts, RR: 7
Reply 2, posted (9 years 6 months 4 weeks 11 hours ago) and read 2182 times:

Thanks, SlamClick, for your response.

I did do a search before posting, (honest).

If it helps anyone, the specific airframe on which I most recently heard this hum was N641UA.


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I understand one is "eavesdropping" on Ch. 9, but, just to clarify, I have never heard this hum on 319/320, 777 or 747s (I am not sure about 757s). Perhaps the IFE eqpmt. on these other airframes have 400 Hz notch rejection filters which suppress it.

thanks



The best time to plant a tree is 40 years ago. The second best time is today.
User currently offlineFSPilot747 From United States of America, joined Oct 1999, 3599 posts, RR: 12
Reply 3, posted (9 years 6 months 4 weeks 11 hours ago) and read 2173 times:

I think I know what you're talking about. It's sort of like a tone that's everpresent whenever the mic button is clicked. I hear it when I'm in the air myself and on the same freq. with airliners.

It's possible that the airline guys can't hear it but everyone else can. But then I'd expect you iron flyers to hear the tone when another airliner comes in on the freq.


User currently offlineDeltaGuy From , joined Dec 1969, posts, RR:
Reply 4, posted (9 years 6 months 4 weeks 10 hours ago) and read 2168 times:

If it's the same hum ya'll are thinking of, I hear it on the Mad Dog in the speakers as the generators whine down, right before the APU grabs control of the bus....or as the engines are being spooled up and the generators are coming on line...I only seem to hear it when the FA's are making a PA, and the speakers are in use....it's an electric sort of whine, kind of how on older cars, the alternator would mess with the car's radio sound.

Never flown UA actually, otherwise I'd be able to know exactly what you're talking about  Smile/happy/getting dizzy

DeltaGuy


User currently offlineWestWing From United States of America, joined Feb 2005, 2134 posts, RR: 7
Reply 5, posted (9 years 6 months 4 weeks 9 hours ago) and read 2124 times:

The hum I am talking of does not seem to be affected or modified by mic keying. When present, it is indeed "everpresent" (in the literal sense of the word). If the cockpit crew elect to not have ATC available on Channel 9 , or switch it off mid-flight (e.g., during a transatlantic crossing), then there is no hum affecting the alternate music "Jazz Session" heard on Channel 9.

The hum can be heard through boarding, pushback, taxi & flight, so it may not be related to a specific source of electric power. It is quite loud, so I am reasonably certain that the cockpit crew do not hear it...it is just heard by the passengers in the cabin tuned to Ch. 9.

rgds



The best time to plant a tree is 40 years ago. The second best time is today.
User currently offlineBicoastal From , joined Dec 1969, posts, RR:
Reply 6, posted (9 years 6 months 4 weeks 8 hours ago) and read 2078 times:

I'm a big Channel 9 fan. I, too, have heard the hum on only the 767. It's actually fairly aggravating. Sometimes I have to turn it off  Sad.

User currently offlineTheiler From United States of America, joined Nov 2001, 633 posts, RR: 1
Reply 7, posted (9 years 6 months 4 weeks 7 hours ago) and read 2072 times:

I know what you are referring to. Both the 75 and 76 seem to exhibit this behavior...

http://www.airliners.net/discussions/tech_ops/read.main/53061/


User currently offlineBrodieBrazil From Canada, joined Nov 2003, 88 posts, RR: 0
Reply 8, posted (9 years 6 months 4 weeks 7 hours ago) and read 2070 times:

i think the whine you guys are talking of is the same one i inquired about a long while back. this thread might help?

http://www.airliners.net/discussions/tech_ops/read.main/87913

i have heard the heavies when i'm flying around on approach/center, and i still hear the hum and wonder


User currently offlineBritPilot777 From United Kingdom, joined Apr 2004, 1075 posts, RR: 2
Reply 9, posted (9 years 6 months 4 weeks 7 hours ago) and read 2043 times:

Hey,

I've noticed it mainly on the 767, once of the 777, but it really does get annoying, strange really.

moheet  Smokin cool



Forever Flight
User currently offlineWestWing From United States of America, joined Feb 2005, 2134 posts, RR: 7
Reply 10, posted (9 years 6 months 3 weeks 6 days 11 hours ago) and read 1906 times:

Thanks for the links to previous threads. I agree what is being heard is probably a 400 Hz frequency (perhaps mixed with some other harmonics). But it is really loud on those 67s !

As for 757s, I did not hear the hum on Ch. 9 on N505UA (configured w/ p.s. cabin layout) .

rgds

WestWing



The best time to plant a tree is 40 years ago. The second best time is today.
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