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Audio Quality Question For VHF ATC  
User currently offlineBOACVC10 From United States of America, joined Jul 2006, 613 posts, RR: 0
Posted (5 years 11 months 2 weeks 6 days 7 hours ago) and read 3754 times:

Disclaimer, I am a ham radio operator, HF, VHF, UHF and also a satcom developer, engineer, so have some familiarity with two-way AM, FM audio communication. .. but not a pilot.

Using a handheld radio, tuned to 118 MHz to 136 MHz I am able to hear ATC ground communication and aircraft communication easily. Given that AM is used, occassionally several transmissions can be heard at the same time on the same frequency, and I am impressed by the professional comm skills of the ATC (my location near KDCA).

My question is multipart:

1) On board aircraft, what is the received quality of the audio transmission ? Is it always 5x9 ?

2) When multiple transmissions are received on the same frequency, how does ATC filter out who is talking, and fast, do they have an indication (sub-carrier identification ?) of who has keyed the mike - or is it upto the skill of the ATC operator.

3) When an ATC communication is sent, I hear the readback almost simultaneously from all the pilots who have had their call sign announced... followed by almost NO delay in the readback - is the audio quality onboard the cockpit that good (speaker -vs- headphone) that it is possible for the pilots who are listening to other chatter, other radios, intra cockpit communication to isolate and respond by keying the mic ? Also, I guess that having a good sharp memory to read back all the details given in a short burst transmission is a typical quality for a pilot right ?

To me, the fluency between TX/RX modes that I hear seems to have no time delay, and I am wondering how could it be so efficient.. I ask, since in HF and VHF radio QSO, it usually takes more than a second or two for each operator to get their radios on the air after being called by a net operator, and also allowing for the possiblity of someone else being on the frequency (listen before sending..)

[I]BOACVC10[I]


Up, up and Away!
9 replies: All unread, jump to last
 
User currently offlineMir From United States of America, joined Jan 2004, 21634 posts, RR: 55
Reply 1, posted (5 years 11 months 2 weeks 6 days 6 hours ago) and read 3746 times:



Quoting BOACVC10 (Thread starter):
1) On board aircraft, what is the received quality of the audio transmission ? Is it always 5x9 ?

As long as you've got line of sight, I've always found it to be very good on the ATC end. Not so much on the pilot end - there can be a few problems here and there, though it's usually a microphone problem rather than a transmission problem.

Quoting BOACVC10 (Thread starter):
2) When multiple transmissions are received on the same frequency, how does ATC filter out who is talking, and fast, do they have an indication (sub-carrier identification ?) of who has keyed the mike - or is it upto the skill of the ATC operator.

It depends. Sometimes you can hear the callsign underneath all the interference. Other times you don't have a clue, and then you have to ask ATC to say again. Generally, it's easier to hear ATC over interference than it is to hear other pilots. Sometimes, pilots will say "blocked", which clues ATC that they got stepped on and they need to repeat themselves.

It's really frustrating when a bunch of people all say "blocked" at the same time.  Smile

Quoting BOACVC10 (Thread starter):
3) When an ATC communication is sent, I hear the readback almost simultaneously from all the pilots who have had their call sign announced... followed by almost NO delay in the readback - is the audio quality onboard the cockpit that good (speaker -vs- headphone) that it is possible for the pilots who are listening to other chatter, other radios, intra cockpit communication to isolate and respond by keying the mic ? Also, I guess that having a good sharp memory to read back all the details given in a short burst transmission is a typical quality for a pilot right ?

We're just that good.  Smile

Sometimes calls do get missed, but when you're flying, you just lock your attention in whenever you hear your callsign (or what you think is your callsign - that's a whole other problem)

Quoting BOACVC10 (Thread starter):
To me, the fluency between TX/RX modes that I hear seems to have no time delay, and I am wondering how could it be so efficient.. I ask, since in HF and VHF radio QSO, it usually takes more than a second or two for each operator to get their radios on the air after being called by a net operator, and also allowing for the possiblity of someone else being on the frequency (listen before sending..)

There is no "listen before talking" when reading back a transmission. The unwritten rule is that if you're waiting to talk and ATC gives an instruction, you wait for it to be read back before you start talking.

Also, if you're listening to an approach frequency, you'll find that most pilots are alert and waiting for instructions because that's the phase of flight when you're expecting a lot of them. If you were to listen to a center frequency you'd probably hear a little more delay between the instructions and the readbacks.

-Mir



7 billion, one nation, imagination...it's a beautiful day
User currently offlineKELPkid From United States of America, joined Nov 2005, 6388 posts, RR: 3
Reply 2, posted (5 years 11 months 2 weeks 6 days 5 hours ago) and read 3731 times:



Quoting BOACVC10 (Thread starter):
Disclaimer, I am a ham radio operator,

So am I  Smile

Quoting BOACVC10 (Thread starter):
Given that AM is used, occassionally several transmissions can be heard at the same time on the same frequency,

Usually (but, of course, not always  Wink ), when this happens with AM modulation, everyone but the simultaneously transmitting stations here a loud squeltch sound, and ATC will usutally come back and say "the last transmission was blocked."

Quoting BOACVC10 (Thread starter):
When an ATC communication is sent, I hear the readback almost simultaneously from all the pilots who have had their call sign announced... followed by almost NO delay in the readback - is the audio quality onboard the cockpit that good

It's usually good enough for the task at hand, I'd say FM modulated audio, full quieting would sound better  Smile

Quoting BOACVC10 (Thread starter):
that it is possible for the pilots who are listening to other chatter, other radios, intra cockpit communication to isolate and respond by keying the mic

When you're expecting a transmission from ATC at certain phases of flight (vectors onto the final approach course, approaching a handoff point, etc), you're listening for ATC...sometimes, on a really busy frequency, I miss a transmmission that I'm not expecting, and it takes ATC a couple of calls to get me (especially in high workload moments, because ATC just becomes background noise, and is, quite frankly, the lowest priority [aviate, navigate, communicate, in that order]).



Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlineJgarrido From Guam, joined Mar 2007, 340 posts, RR: 0
Reply 3, posted (5 years 11 months 2 weeks 5 days 19 hours ago) and read 3677 times:



Quoting BOACVC10 (Thread starter):
2) When multiple transmissions are received on the same frequency, how does ATC filter out who is talking, and fast, do they have an indication (sub-carrier identification ?) of who has keyed the mike - or is it upto the skill of the ATC operator.

If you're lucky (and maybe the two planes are far enough apart?) you can still make out what both planes said. Sometimes you can pick up on a part of a callsign, altitude, fix, etc. and you can use that to get just one of the planes to repeat themselves. E.g. "Aircraft at FL370 say again". After the second or third call I sometimes remember what the voice of certain pilots are and associate them to their plane. It's not something I concentrate on, but subconsciously sometimes I make the right "guess" when I didn't hear the callsign. Also we have a wide variety of nationality's that fly though our airspace so you can make a guess on who called based on the accent.

Quoting BOACVC10 (Thread starter):
3) When an ATC communication is sent, I hear the readback almost simultaneously from all the pilots who have had their call sign announced... followed by almost NO delay in the readback - is the audio quality onboard the cockpit that good (speaker -vs- headphone) that it is possible for the pilots who are listening to other chatter, other radios, intra cockpit communication to isolate and respond by keying the mic ? Also, I guess that having a good sharp memory to read back all the details given in a short burst transmission is a typical quality for a pilot right ?

Maybe I should consider moving back east, because around here it can get very frustrating to repeat one's self. Not to mention everyone with a 3 in their callsign reading back a clearance to JAZ943.  Sad Oh well.


User currently offlineBOACVC10 From United States of America, joined Jul 2006, 613 posts, RR: 0
Reply 4, posted (5 years 11 months 2 weeks 5 days 17 hours ago) and read 3659 times:



Quoting Jgarrido (Reply 3):
If you're lucky (and maybe the two planes are far enough apart?) you can still make out what both planes said. Sometimes you can pick up on a part of a callsign, altitude, fix, etc. and you can use that to get just one of the planes to repeat themselves. E.g. "Aircraft at FL370 say again". After the second or third call I sometimes remember what the voice of certain pilots are and associate them to their plane.

So, comparatively speaking is the dynamic range of VHF AM audio transmission, better, do you all think, than that of a FM transmission (88-108 MHz) or perhaps a digital audio CD player (44.1 kHz BW) ?

If you were to create a scale of audio quality, with PSTN (64 kbps) fixed line quality in the middle, and to the extreme left, CD Quality sound (44 kHz) and HF quality sound to the far right, what would your opinion of VHF onboard *audio* quality be ? Would that be due to the better quality headphones, or use of a better quality radio ? I'm discounting range and TX power here, just focusing on audio quality as perceived by pilots.

BOACVC10



Up, up and Away!
User currently offlineJgarrido From Guam, joined Mar 2007, 340 posts, RR: 0
Reply 5, posted (5 years 11 months 2 weeks 4 days 17 hours ago) and read 3547 times:



Quoting BOACVC10 (Reply 4):

I really am not that qualified give that detailed of an answer. What I would say is that I the quality slightly below an average AM radio station. That is, if I remember what AM radio sounds like. There aren't any AM stations out here so I haven't heard one in a while. However, comparatively speaking the expectation in sound quality is low. If there's some cracking or "pegging" I don't really care as long as I can make out what altitude a plane reported at when he checks in at the boundary of my airspace (250nm) I'm satisfied. I also have a feeling the speakers installed in our loudspeakers, headsets and handsets aren't exactly "audiophile" grade for that same reason.


User currently offlineSCCutler From United States of America, joined Jan 2000, 5520 posts, RR: 28
Reply 6, posted (5 years 11 months 2 weeks 4 hours ago) and read 3406 times:

It is interesting how well I can mentally filter out extraneous stuff on frequency, and suddenly snap to attention when ATC calls me- I always forget, when someone who is not familiar with either flying in general, or my tail number in particular, is flying with me, that they do not know to stop talking when the controller is talking to ME.

We are blessed with exceptionally good controllers here in the DFW area, too- grace under pressure.



...three miles from BRONS, clear for the ILS one five approach...
User currently offlineN353SK From United States of America, joined Jun 2006, 822 posts, RR: 0
Reply 7, posted (5 years 11 months 1 week 6 days 18 hours ago) and read 3385 times:

I've always heard (off the record) that AM is preferential to FM in ATC because with AM, you can hear it when somebody gets stepped on, whereas with FM the receiver just focuses in on the stronger signal.

As for quick readbacks, like others have said pilots frequently already know what they're going to hear. Also, it helps that the mic key button is on the yoke/stick.


User currently offlinePGNCS From United States of America, joined Apr 2007, 2825 posts, RR: 45
Reply 8, posted (5 years 11 months 1 week 6 days 16 hours ago) and read 3373 times:



Quoting BOACVC10 (Thread starter):
1) On board aircraft, what is the received quality of the audio transmission ?

VHF varies from excellent to horrible depending on a myriad of things including range, weather, and condition of antennas (e.g. icing). Sometimes it seems great when you wouldn't expect it to, sometimes it is wretched when you expect it to be great.

Quoting BOACVC10 (Thread starter):
2) When multiple transmissions are received on the same frequency, how does ATC filter out who is talking, and fast, do they have an indication (sub-carrier identification ?) of who has keyed the mike - or is it upto the skill of the ATC operator.

Sometimes they don't. Sometimes you can still make out a transmission when another station is talking, sometimes not. All told most controllers and professional pilots do a good job listening up and figuring it out; if not you ask for the transmission again.

Quoting BOACVC10 (Thread starter):
3) When an ATC communication is sent, I hear the readback almost simultaneously from all the pilots who have had their call sign announced... followed by almost NO delay in the readback - is the audio quality onboard the cockpit that good (speaker -vs- headphone) that it is possible for the pilots who are listening to other chatter, other radios, intra cockpit communication to isolate and respond by keying the mic ? Also, I guess that having a good sharp memory to read back all the details given in a short burst transmission is a typical quality for a pilot right ?

The pilots want to get the reply in as quickly as possible so ATC can get on with their next instruction. Good communication skills are important for pilots.

Quoting Mir (Reply 1):
It's really frustrating when a bunch of people all say "blocked" at the same time.

Yes it is.

Quoting SCCutler (Reply 6):
We are blessed with exceptionally good controllers here in the DFW area, too- grace under pressure.

I'm curious on this one: do you actually fly into DFW proper or a satellite airport, as DFW controllers don't have a particularly good reputation. The multiple arrival and runway changes they are notorious for create a much higher workload for the crews than comparably busy airports (ORD, ATL, etc.) and "grace under pressure" would be the very last moniker I would hang on them. More like "competent but testy."


User currently offlineSCCutler From United States of America, joined Jan 2000, 5520 posts, RR: 28
Reply 9, posted (5 years 11 months 1 week 5 days 4 hours ago) and read 3277 times:



Quoting PGNCS (Reply 8):
Quoting SCCutler (Reply 6):
We are blessed with exceptionally good controllers here in the DFW area, too- grace under pressure.

I'm curious on this one: do you actually fly into DFW proper or a satellite airport, as DFW controllers don't have a particularly good reputation. The multiple arrival and runway changes they are notorious for create a much higher workload for the crews than comparably busy airports (ORD, ATL, etc.) and "grace under pressure" would be the very last moniker I would hang on them. More like "competent but testy."

Ah, I am not a 121 pilot, and I have never yet landed at DFW itself. I am, however, based at ADS, into which one can never fly without sequencing by DFW TRACON, and I use their services every single time I fly, whether VFR or (most often) IFR.

But, what you describe may well be the case, and I'd be without a clue.

I prefer DFW TRACON's service to (for example) Houston's, although the award for best service I have ever gotten is shared between NorCal Approach, and Pensacola (I know, not exactly equivalent).



...three miles from BRONS, clear for the ILS one five approach...
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