A320 ATC Antennas

skywalker92 · Thu Mar 03, 2016 2:59 pm

1) Can any one explain me what is the purpose of yellow color ATC antennas located at forward lower fuselage of the aircraft. Although VHF antennas are the ones use for ATC communication why they are called ATC antennas? As highlighted in the attached diagram what are the 2 ATC mode s antennas? Are they performing the same function as lower fuselage yellow ATC antennas?

2) According to my knowledge TCAS antenna is used to detect proximate traffic vicinity to the aircraft in collaboration with the transponder . Am I correct? Is it the one transmits the 1090 MHZ signal?

thanks a lot!!

Regards,
Skywalker92

Starlionblue · Thu Mar 03, 2016 3:30 pm

Quoting skywalker92 (Thread starter):

1) Can any one explain me what is the purpose of yellow color ATC antennas located at forward lower fuselage of the aircraft. Although VHF antennas are the ones use for ATC communication why they are called ATC antennas? As highlighted in the attached diagram what are the 2 ATC mode s antennas? Are they performing the same function as lower fuselage yellow ATC antennas?

In AirbusLand, the "ATC" system refers to the transponders. VHF is referred to as "VHF". If nothing else, VHF can be used to communicate with other stations than ATC, for example other aircraft or company ops.

Mode S is a transponder mode that transmit a multitude of information to ATC. "Old school" transponder have only Mode A (squawk code) and Mode C (altitude reporting).

Quoting skywalker92 (Thread starter):
2) According to my knowledge TCAS antenna is used to detect proximate traffic vicinity to the aircraft in collaboration with the transponder . Am I correct? Is it the one transmits the 1090 MHZ signal?

It sees the transponders of other aircraft.

As I understand it, the TCAS antenna would receive on 1090, while the ATC antenna would transmit on 1030.

[Edited 2016-03-03 07:52:13]

[Edited 2016-03-03 07:54:13]

skywalker92 · Thu Mar 03, 2016 5:05 pm

Quoting Starlionblue (Reply 1):
VHF can be used to communicate with other stations than ATC, for example other aircraft or company ops.

So what is the frequency that is used to communicate with ATC? and is it done with yellow color ATC antennas?

Quoting Starlionblue (Reply 1):
TCAS antenna would receive on 1090, while the ATC antenna would transmit on 1030.

you are correct, I have made a mistake...

I do not get an answer for this.. What is the purpose of ATC antennas?

boeingfixer · Thu Mar 03, 2016 9:18 pm

Quoting skywalker92 (Reply 2):
I do not get an answer for this.. What is the purpose of ATC antennas?

Don't think of the term ATC as in communications. The ATC antennas are transponder use antennas only.

VHF and HF antennas are used for communications.

Cheers,

John

skywalker92 · Fri Mar 04, 2016 12:58 am

That means VHF and HF antennas are used for communication while all ATC antennas and TCAS antennas are used for transponder tasks??

Starlionblue · Fri Mar 04, 2016 1:00 am

Starting from "first principles", if you will, we communicate with ATC basically in three basic ways.

- Audio control panels for voice. Voice comms use VHF and HF.
- CPDLC for datalink comms. CPDLC also uses VHF and HF (and satcom) to send and receive data.
- ATC system, which is the transponders, for position, altitude and with Mode S a multitude of other data. ADS can be seen as an extension of this, though AFAIK it does not use the transponders..

Importantly, while we talk to ATSUs (Air Traffic Service Units) with both audio and CPDLC, these are not referred to as "ATC systems". "ATC" is the transponders. When we say "ATC?" in the checklist, this refers to setting the transponder.

Quoting boeingfixer (Reply 3):
Quoting skywalker92 (Reply 2):
I do not get an answer for this.. What is the purpose of ATC antennas?

Don't think of the term ATC as in communications. The ATC antennas are transponder use antennas only.

While the ATC antennas communicate, as in respond to transponder interrogations, they are not used for voice comms to an ATSU (Air Traffic Service Unit).

skywalker92 · Fri Mar 04, 2016 3:05 pm

I am pretty ok with that now !
Thanks a lot for your answers...

HAWK21M · Sun Mar 06, 2016 8:25 am

Quoting Starlionblue (Reply 1):

In AirbusLand, the "ATC" system refers to the transponders

Its the same on Boeings too.

Two Antennas for added reliability to the system, as one can be deffered.

skywalker92 · Fri Mar 11, 2016 11:21 am

Do any one explain me about the frequency used in those antennas ...

Regards,
Skywalker92

Starlionblue · Fri Mar 11, 2016 1:45 pm

Quoting skywalker92 (Reply 8):
Do any one explain me about the frequency used in those antennas ...

Didn't we already go through this?

Quoting Starlionblue (Reply 1):
As I understand it, the TCAS antenna would receive on 1090, while the ATC antenna would transmit on 1030.

And you said...

Quoting skywalker92 (Reply 2):
Quoting Starlionblue (Reply 1):
TCAS antenna would receive on 1090, while the ATC antenna would transmit on 1030.

you are correct, I have made a mistake...

skywalker92 · Sun Apr 17, 2016 1:59 pm

got everything starlionblue... thanks a lot..

Transponder uses TCAS antenna to transmit its parameters,those parameters are received by the aircraft at its vicinity. TCAS antenna is not used to transmit details to the ground that means to Secondary Surveillance Radar and ADSB receivers. The details that received by Secondary Surveillance Radar and ADSB receivers are transmitted by ATC antennas located at the aircraft.

TCAS transmits at 1090 MHz and receives at 1030 MHz.
ATC antenna uses same frequencies but their target is not aircrafts at vicinity but Secondary Surveillance Radar at ground.

Is this true? This is what I filtered from this topic and lot of readings in the internet.

skywalker92 · Sat Oct 01, 2016 9:51 am

Al things are here...

http://www.howtheyfly.com/2016/10/autom ... lance.html

Regards,
Skywalker92

RotateAero · Sat Oct 08, 2016 2:24 am

OK.... I think quite a few of your questions have been answered, but I'll throw in what I know. On most (if not all) aircraft, ATC antennas are generally referred to as the system sending Mode A/C or ADS-B information to Air Traffic Control centers. There is "no" voice communication on ATC antennas. VHF or HF "Comm" antenna's are used for voice communications. VHF Comm antennas are usually around 14-18 inches in length and seem to be well suited in removing skin from your scalp. ATC antennas and DME antennas are actually the same. They're short, about 1-1/2 inch. Both the ATC and DME transponders use the exact same frequency. While one is "talking" the others are suppressed.

Now to TCAS. The TCAS antenna is usually fairly flat (about 1/2 inch high) and somewhat round with a diameter close to 6 inches. There are four elements in each TCAS antenna. It "does not" transmit. It compares incoming signal strength on each of the four elements and derives a position "direction" of the transmitting aircraft in relation to your own. This information is used by the TCAS Processor for cockpit display and collision avoidance via signals sent "out" from the ATC transponders.

RotateAero · Sat Oct 08, 2016 2:53 am

A couple things I forgot...... modern ModeS ATC transponders use two antennas each. One up top and one below. DME transponders use only one each and they're mounted on the bottom. So in total, there are six antennas. Two up top and four below. Because of their looks, they're sometimes referred to as "shark's fins."

There is only one TCAS Processor installed, but it has a upper and lower antenna. Each antenna has four separate co-ax cables, one for each element. The processor rack plug has most of the space occupied by the eight co-ax connectors coming in.

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