muffled comms from london atc
 

Quick question? Is it just me or are London atc all muffled on the r/t. Never used to be the case, but over last couple of months I have noticed the need to turn up the volume on the London frequencies to hear the ground controller, yet airborne users are blasting out loud and clear.

Have you guys and girls changed headsets or something?

Which airport do you experience it at? "London" is a little vague.

I understood this to be the ground controller as in person on the ground, and airborne users as other pilots.
could it be something to do with vccs and new headsets that the tma have had since the move down south?

The VCCS or the headsets not up to scratch... never. Surely that would not be allowed to happen :ugh:

hapzim
 

Please mention it at the time, if possible. It may be something as simple as moving the mike closer to our mouth, or may permit us to check with other aircraft on frequency. We can also report it internally for immediate monitoring and investigation..........if you don't tell us, we won't know.

Hi I have mentioned it more than once over the last couple of months, apparent on most london(swannick) freqs with different controllers male and female. Other aircraft loud and clear as are airfield controllers, so don't believe it's our end.

Muffled requiring more volume and just harder to understand, also approaching departing from different sectors, so not one area.

The headsets in AC Ops room have all been replaced this week. Is it any better?

Say again?

No

To be honest it sounds like you have a narrow freqency filter put on.

Makes everything sound monotone and muffeled and unfortuantely the frequency band is about the same as the engines on a TP. Could do with it a bit broader or moved higher up the freq range.

I presumed it's some sort of bandwidth reducing exercise.

Just a thought from a non atc/aircrew person.

Is this on London TMA freqs or just enroute sectors. If just enroute then wondering if 8.33 khz freqs could be a factor as I understand some freqs have been "converted" and may therefore sound different.

I too have noticed a huge reduction in the quality of transmissions by pretty much all of the UK major units recently (London airways, Manchester app & control freqs), Scottish. I can only describe it as slightly distorted and muffled - As its across the board, my guess is the tech folk have done some sort of countrywide 'upgrade' to the transmitters.

When I was there in the late 90's it always sounded like they were under water compared to where I used to fly.

Reminds me of talking to (or perhaps I should say attempting to communicate) with Casablanca Control in the 1980s. I used to joke that all the controllers there had to come to work with a bucket which they placed over their heads when they went on duty. Very occasionally you would get a clear one - that's because he had forgotten to bring his bucket with him.

It was so bad I decided to file an MOR. The upshot was that the a/c equipment was on frequency (I recall we were on 25 kHz spacing then) but the ground control was slightly off leading to distortion etc.

I have also noticed a reduction in quality in the UK recently. By comparison when you talk to Maastricht or Rhein ATC they seem to be much clearer.

The Sennheiser headsets used in AC (HME 64) are currently being modified with an improved cable made with a steel core instead of the original copper core. This is due to premature headset failure caused by the copper core breaking down.
Those leads don’t like being run over by the ATCO's chairs:ugh:

With regards quality, pls raise it at the time with the controller. Could be a number of reasons. The mic on the headset needs to be 2 finger lengths away from the mouth and facing the mouth!!!
It's not easy to tell which way the mic faces when the wind "sock" is on but it makes a big difference to quality if it's facing the wrong way.

Slight thread creep, but is the London frequency aroung Gibso going to be fixed. I seem to remember it was due to a lack of transmitters that you got the 'head in dustbin' effect

It's definately worth reporting at the time. The least we will do is report it to systems control who can monitor and investigate the situation. If we feel it is a significant reoccuring problem, we can submit an MOR. Unless you tell us about it at the time... we won't know! :cool:

I seem to recall that comments were made (in this forum) when the phenomenon first surfaced shortly after Swanick became operational. It was not unusual to regularly hear comments from crews about the qulaity of transmissions from LATCC. The 'head in a bucket' transmissions didn't go away but crew comments (on frequency) certainly did; I can't recall the last time I heard any crew comment on the transmission quality, possibly because it was so normal that nobody bothered to say anything.

Sometimes the guys and gals in the Iron Toffee Apple at LHR sound like they're talking down a long drain pipe.

Which I suppose they are:bored:

VCCS?
 

I've heard that the VCCS system has had problems with voice quality, but these should have been fixed by a recent update. I suggest that any pilots having problems hearing either tell the controller at the time or (e.g. if the frequency is too busy) file a report. Information is the key to solving this kind of problem.

Audio Quality Investigations
 

There are a number of investigations running presently to look into this issue. NATS Engineering are taking it very seriously. We have to have specific instances reported to us (date, time, frequency, position) to correlate results and look for any patterns that may emerge.

A characteristic that has been uncovered is that a large proportion of aircraft receivers are not set up as well as they could be and where NATS uses two transmitters with off-set carrier frequencies to get as much coverage for a sector as possible, the receiver gets "confused" as to which transmitter to listen to and refuses to lift the mute. This results in apparent 'dead' spots for particular aircraft types using these receivers. There has been a safety bulletin covering this issue describing the symptoms and possible mitigation. Work at a European level is being done to change the receiver specification to eliminate the effect, but will take some time to put into place.

On 8.33kHz use: because a single transmitter is used (at any one time) on a frequency, the reported audio quality has improved, despite a slight reduction in the bandwidth. It can be used to overcome some effects related to the issue I describe above.

Audio level seems to be simply down to microphone position. End to end system checks using calibrated test equipment has shown that the audio levels are correct, but when a microphone is correctly positioned, the problem goes away.

If you would like me to keep you posted here as to progress on these issues, I am pleased to do so as it seems to be more avidly read than any other means of communication!!