LHR approach; muffled audio?

[TCTC]

I wonder whether it is intentional that 119.725 has rather muffled audio compared with most other channels?

[HEATHROW DIRECTOR]

If there was a problem I am sure it would have been noticed and reported. Sounds fine where I am.

[Cough]

TCTC - Given your previous thread starts of LHR Fire/Tower and now approach having distorted/muffled radio, maybe it's not LHR's kit thats to blame....

[HEATHROW DIRECTOR]

I hadn't seen those posts but given that the Heathrow Approach suite is about 50 miles from Heathrow Tower I don't think there's a connection.

[Nimmer]

Anybody listen to Gatwick regularly? We are constantly having to repeat ourselves due to missed calls.

I am convinced the R/T is not clear enough.

[Del Prado]

Gatwick problems might be down to crossing and poor RT discipline on a frequency which has become increasingly busy recently.

Long winded and slowly delivered first calls including every item except what the pilot had for breakfast tend to tie up the frequency for too long (particularly as someone else is sailing through the localiser!)

I've not noticed the quality of the frequency at Gatwick being an issue as much as the RT discipline and if the RT is being tied up more than necessary then there will be more crossed and blocked transmissions.

[JuicyLucy]

The audio quality from Swanwick TC is generally not brilliant, although it better than when LATCC first moved. Mixture of headset and the digital techniques used to send the audio to remote transmitter/receiver sites. Some sectors are better then others, and the newer designs of aircraft radios seem to suffer more. I can now understand the French better than the English!

[EGPFlyer]

I find Essex radar sound quality really bad. The rest of London seems OK

[TCTC]

Many thanks for all the interesting comments.

(It might help the discussion if I humbly delcare my credentials:
B.Sc. Communication Engineering and several decades experience in the technology and use of radio communications).

[TelsBoy]

Ofter there's nowt wrong with the kit, more to do with users' mic positioning that muffles audio.


Have seen pilots who are prcatically eating the mic, others who have it about a foot away, all that can be heard is a whimper above the carrier wave. And ATCOs can hold/wear headsets at all sorts of bizarre positions... but its the CAP670-compliant kit that's blamed...

[Juggler25]

The audio quality from Swanwick TC is generally not brilliant, although it better than when LATCC first moved. Mixture of headset and the digital techniques used to send the audio to remote transmitter/receiver sites. Some sectors are better then others, and the newer designs of aircraft radios seem to suffer more. I can now understand the French better than the English!

Swanwick is moving to VOIP in the next 18 months or so. Who knows if this will be better or worse.

I hate working 787's as their radio quality is awful. I do wonder if it's to do with the composite construction not accentuating the signal as much as metalic construction does?

[Cough]

Juggler -- Have you raised those concerns further up? Can't say I notice any particular 787 effects from our side + also listening to colleagues also flying them...

Genuine Q. Is it all 787's? Or is the audio quality different between operators? (Thinking is this a headset thing, or aircraft radio...)

[le Pingouin]

The 787s of certain operators have a characteristic high pitched background hum - not enough to affect comms but distinctive enough that I know it's a 787 calling just from the sound. Somewhat reminiscent of Thunderbird 2 ;)

[HEATHROW DIRECTOR]

Used to happen on BAC 1-11s too - inverter whine I believe.

[Juggler25]

Genuine Q. Is it all 787's? Or is the audio quality different between operators? (Thinking is this a headset thing, or aircraft radio...)

It's definitely all of them however BA's are worse than others. When BA first got them they did several (training?) flights in and out of Manston and the pilots kept asking me about the RT quality as they were noticing it was worse than what they were expecting from a new aircraft type. It's weird because you can hear them fine but the quality is no way near as good as other aircraft. Strange one...

[Cough]

Interesting - I wonder if its our headsets then as you say we are worse than others. I know there are folk looking at replacements as the Sennheisers that we currently use aren't being made anymore...

[Gonzo]

Concur with Juggler25. One can identify the 787 of certain operators just because of the high pitch whine on the carrier wave, and the speech does sound significantly more muffled than other types.

Upon reflection, I think all 787s have the muffled audio; but add in the whine then in a busy ops room with lots of ambient noise going on, and perhaps a crossed transmission, it gets quite difficult sometimes to understand some of them.

[Eric T Cartman]

@ Heathrow Director
You'll recall, I'm sure, that the BAC1-11 500 series transmissions always ended with a 'Houston Control' type bleep :-)

[chevvron]

Used to happen on BAC 1-11s too - inverter whine I believe.

Worst I've heard is a Chinook.(Rotor gearbox whine so I'm told)

[Brian 48nav]

I was going to post earlier with this retired old git's theory, that when a brand new aircraft off the line leaves the factory and is put through its paces in the air, the test pilots are using a particular make and even quality of headset, and then maybe the customer buys a different make.

I checked this out with the off-spring ( not the Swanwick ATCO, but the Airbus TP ) and it seems for once it my life I was absolutely right!

He used to fly for Richard's airline and says their headsets were so cheap and poor that no decent music fan would ever use one! Add to that,he said, the fact that many pilots take their hats off and go to loudspeaker above a particular FL.

[HEATHROW DIRECTOR]

If anyone on here has worked with Aeroflot or Russian AF in the 60s they'll know what muffled R/T is!

[chevvron]

If anyone on here has worked with Aeroflot or Russian AF in the 60s they'll know what muffled R/T is!

Wasn't helped by them using interpreters who had no aviation knowledge. The interpreter couldn't speak loudly in case he was heard over the RTF, he would just tell the pilot what to say and the pilot would repeat it parrot fashion. I've actually heard an interpreter shout at the pilot when the latter said the wrong thing.

[Uplinker]

With a pre-flying background in broadcast quality comms engineering, my two pence worth:

Please everybody use a windshield on your microphone. If you don't, the receive station hears a breathy/scratchy sound accompanying your speech, along with the 'plosive'sounds: 'B' 'P' etc, which distort your transmissions and makes them less intelligible to the receiver. This will mean you have to repeat yourself more often.

If you don't use a windshield, the microphone will gradually fill up with spit and dust etc which will cause it to reduce and distort the electrical output.

A noise cancelling microphone needs to be close to and directly in front of the mouth to work properly - so that if you pursed your lips, they would touch the windshield. Even if the microphone is a only couple of inches away from the mouth, or below the mouth, the person receiving your transmission will hear mostly background noise - "say again?". Feel the microphone through the windshield to make sure it is facing your mouth and has not twisted to be edge on.

Speak normally but key the PTT a split second before speaking. The transmitter will not transmit instantly you key the switch, but takes a moment to check the transmit circuits and frequency are stable and correct before passing your speech. Unless you wait a split second your first word(s) will be clipped off: "station calling?".

I often get a hard time for saying these things, but it would improve the clarity of comms a lot if we could all follow these easy and simple steps. :ok:

[HEATHROW DIRECTOR]

Professional pilots and ATCOs should know how to use microphones and most use lightweight headsets anyway.

[chevvron]

Windshield? Doesn't get windy in ATC ops rooms unless certain people have eaten curry the night before.

[Dan Dare]

Professional pilots and ATCOs should know how to use microphones

unfortunately pilots/ATCOs don't come with innate knowledge of such things and it is no longer taught so unless it's pointed out to them they never know! Some refuse to believe even when it has been pointed out to them.

I'm grateful for people like Uplinker giving the occasional nudge on the basics :D

Another basic that pilots are sometime guilty of:- using a hand-mic in front of a loudspeaker. OUCH!

[HEATHROW DIRECTOR]

Well, they ought to be familiar with CAP 413 and there are full details of microphone usage there.

[Nimmer]

Who to chat to in the rest room. The person who can quote CAP 413, or the person who has a life???

Answers on a postcard..........

[HEATHROW DIRECTOR]

Good luck with your LCE Nimmer.

[Nimmer]

Get up to date HD called a UCE now!!!

Don't think I have ever been asked anything out of CAP 413, however I need some help getting to sleep will start reading.