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Technical RT and telephone question

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Technical RT and telephone question

Old 30th Jan 2022, 07:35
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Technical RT and telephone question

A controller is at his console and is on the telephone, via headset, to another controller elsewhere for whatever reason. During the course of the telephone call, the controller has to transmit to an aircraft. Would that transmission and the reply from the aircraft be heard by the other controller (i.e. sent down the phone line) or not ? Does it depend on the radio and telephone equipment, the VCCS and how it's all configured ? Thankyou.
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Old 30th Jan 2022, 09:25
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When I was operational (10 years ago) if you transmit to an aircraft while the landlines is open, the ATCO at the other end of the landlines would hear your transmission but would not hear the aircraft's reply.
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Old 30th Jan 2022, 09:27
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It depends on the equipment and how it’s being used. At my current unit any pilot heard down the telephone line would be a sign that the radio is on speaker or turned up so loud in the headset that the telephone mic can pick it up.
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Old 30th Jan 2022, 10:01
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The designer of the comms switching unit could configure it either way round, but I would say that it would be undesirable to combine the whole telephone circuit with the RT voice circuit.

There will be a 2 wire to 4 wire unit in the comms box to separate the incoming 2 wire telephone circuit to feed the received telephone audio to the local headset ear speakers and feed the local headset boom microphone down the telephone line.

The distant telephone user would need to hear if the local ATC had to break-off and transmit on the RT, so it would be useful for the distant user to hear the local ATC boom mic all the time - even when the RT PTT was pressed - so the distant telephone user would know to shut up for a moment. Can't think of a reason to put the received telephone audio onto the local RT voice circuit.

(Hope that makes sense).
.
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Old 30th Jan 2022, 10:16
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Thankyou everyone. Having a system designed so the controller on the other end of the telephone can hear when the other bod is TXing to an aircraft is desirable. Can't have anyone thinking the line has gone dead. But no need for aircraft TX to go down the phone line and vice versa. I suppose any configuration is possible with modern VCCS. When a controller only has a single headset microphone for both RT and telephone, it stands to reason that some shared audio is possible, IYSWIM.
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Old 30th Jan 2022, 10:42
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Shouldn't RT read RTF?
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Old 30th Jan 2022, 10:49
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Originally Posted by TCAS FAN View Post
Shouldn't RT read RTF?
Probably. I'm not in the ATC business so excuse my ignorance. A former ATC friend always uses RTF.
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Old 30th Jan 2022, 21:25
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no, Voice to RT has higher priorty than phone, it shuts it off.
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Old 31st Jan 2022, 22:59
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As to the original question, I guess it's down to the technical setup.

Originally Posted by Mooncrest View Post
Having a system designed so the controller on the other end of the telephone can hear when the other bod is TXing to an aircraft is desirable.
I don't agree with this one though. Would like to hear other controllers opinions.
The risk would be the transmission on freq be mistaken for what it's being discussed at the phone. Also, where's the problem with a clear and quick "standby" to the guy on the phone?
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Old 1st Feb 2022, 07:37
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All the systems I’ve used, including a VOIP VCCS under testing right now, allow the transmissions to be heard by the other controller, but not the incoming aircraft transmissions.
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Old 1st Feb 2022, 17:01
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There are some detailed requirements for ATC communications systems in the UK which are not found in international standards. The UK is sometimes accused of over-engineering things and in this case I think it is with good reason. Amongst other things, there is a requirement (I think, possibly it's a strong recommendation only) for headsets to be available. When headsets are used, the normal operational mode is that when RTF transmissions from aircraft are received they are heard in both ears, if a landline is open then the RTF transmissions are in one ear and the landline in the other. When a landline is open, when the controller talks the person on the other end of the landline(s) hears what is said; this includes anything said while the controller is transmitting to an aircraft. In the old days, when transmitting, the controller also got a low-volume feed into the headset, usually called a sidetone, from a receiver separate from the rest of the comms system. This allowed the controller to detect whether his/her transmissions were actually being broadcast and also to pick up instances of cross-transmission where the controller transmitted at the same time as another station (because they would hear the whine as the two signals interfered with each other).

With the introduction of some VoIP VCCS delays in broadcasting a controller's transmission mean that an off-air sidetone can produce a disconcerting 'echo' in the headset and the sidetone can be derived from the VCCS at a point close to the transmitter - if I understand things correctly, this will continue to provide a nice warm feeling to the controller but, in fact, provides no confirmation that the transmission actually went out and no protection from crossed transmissions which, potentially, could go completely undetected. I have no involvement in the implementation of any such systems but I'd be interested in any thoughts (or corrections to my current understanding) from Gonzo or anyone else with hands-on experience with modern systems.
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Old 1st Feb 2022, 18:49
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I will reserve judgement on VOIP VCCS systems, if youíll allow me.

Yes, delays can be an issue, and a local side tone can be used, if considered appropriate.

I should add that there are ways that a controller can become aware of a crossed transmission.
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Old 2nd Feb 2022, 04:41
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Interesting subject. I remember when EGNM had its own home-built RDCS and TDCS and I had the opportunity to listen in a few times. There was certainly RTF sidetone fed to the headset - I don't know the source. The controller would usually have up to three RTF RX frequencies selected - whichever was also on TX gave the loudest volume which I guess was deliberate. I remember the volume on the external telephone lines was on the low side but the internal intercom between control positions was much louder - it was a simple ring-main system connecting all positions. Now it's a Frequentis VOIP system. I don't know how it compares.

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Old 3rd Feb 2022, 02:38
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Iím in Shannon. When I transmit, I also hear myself in my ears from a receiver co-located with my transmitter (or sometimes from a different receiver for the first second or so, when the black box of the Best Site Selection system we have thinks thatís what I want to hear, for some unexplained reason).

When I have a phone line open, I get radio in one ear and phone in the other. If the controller Iím speaking to on the phone is transmitting on their radios, I hear their transmission but usually not the response from the aircraft (occasionally I hear it weakly in the background, but I suspect thatís just that they have their earphones turned up very loud or they have radio on their speakers as well Ė itís never been loud or clear enough to think itís being relayed from the radio into the phone line). Thatís certainly true for when I talk to other controllers in my unit or Dublin, London, or Scottish
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