seb146
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Air Traffic Control Frequencies

Fri Nov 09, 2018 12:47 am

I have a certificate in broadcasting and had a ham radio licence for a long time, so I understand the different band technologies. Not the right term, but I know 2 Meter ham radio works differently than 10 Meter and FM works differently than AM than shortwave.

I have always thought that, because air traffic control frequencies are near ham radio 2 Meter band, it works the same; that is: line of sight. Being at 35,000 feet has a different line of sight than being on the ground. Are they talking directly to the ATC or is it a repeater system? I would think the repeater system would be painfully slow, so a very strong transmitter?
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GalaxyFlyer
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Re: Air Traffic Control Frequencies

Fri Nov 09, 2018 1:02 am

Remote ATC comm sites relayed to the ATC Centers via landline of microwave. There’s a network called Aeronautical Fixed Telecommunications Network (AFTN) that handles traffic between centers and Flight Information Regions.

https://en.m.wikipedia.org/wiki/Aeronautical_Fixed_Telecommunication_Network

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fr8mech
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Re: Air Traffic Control Frequencies

Fri Nov 09, 2018 1:06 am

They are line-of-sight, no repeaters. A quick look at the AMM (B747-8) tells me the VHF transceiver has minimum of 25 watts of output power.

Is 25 watts powerful? I've no idea, though I do seem to recall that 5 watts was pretty powerful for a CB. Yes, I know that CB and VHF are on different parts of the frequency spectrum.
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Starlionblue
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Re: Air Traffic Control Frequencies

Fri Nov 09, 2018 2:16 am

fr8mech wrote:
They are line-of-sight, no repeaters. A quick look at the AMM (B747-8) tells me the VHF transceiver has minimum of 25 watts of output power.

Is 25 watts powerful? I've no idea, though I do seem to recall that 5 watts was pretty powerful for a CB. Yes, I know that CB and VHF are on different parts of the frequency spectrum.


There are plenty of places that use repeaters on the ground.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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fr8mech
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Re: Air Traffic Control Frequencies

Fri Nov 09, 2018 3:07 am

Starlionblue wrote:
There are plenty of places that use repeaters on the ground.


Really? I find that strange. In all the training I've had surrounding Comm & Nav systems on aircraft, we've never talked about repeaters in the comm system.
When seconds count...the authorities are minutes away.
Unless it's expressly prohibited, it's allowed.
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Woodreau
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Re: Air Traffic Control Frequencies

Fri Nov 09, 2018 3:09 am

As far as I know, there are antenna farms throughout an ATC sector. Sometimes ATC will ask an aircraft to do radio checks, and over the same frequency, they communicate with the aircraft from different transmitters / same frequency.
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GalaxyFlyer
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Re: Air Traffic Control Frequencies

Fri Nov 09, 2018 3:27 am

The repeaters are on the ground, pilot talks to an ATC Remote Communications Outlet, which is then sent via landline or microwave to the center. Some are amazing like on Greenland or in the remotest Africa.

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fr8mech
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Re: Air Traffic Control Frequencies

Fri Nov 09, 2018 5:00 am

Well, well, you learn something new everyday.

So, are the repeaters used to increase the range over the "theoretically optimal" 200NM range, or just to provide coverage where line-of-sight may be impeded by terrain?
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Unless it's expressly prohibited, it's allowed.
You are not entitled to a public safe space.
 
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Starlionblue
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Re: Air Traffic Control Frequencies

Fri Nov 09, 2018 5:13 am

fr8mech wrote:
Well, well, you learn something new everyday.

So, are the repeaters used to increase the range over the "theoretically optimal" 200NM range, or just to provide coverage where line-of-sight may be impeded by terrain?


I think mostly to increase range. Two places I can think of with repeaters are The Philippines and Australia. In Australia you might be talking to Brisbane Center and they'll periodically ask you "change to my frequency xxx.xx". Same station, different frequency in another area, and often the same on shift guy for a long while as you are passed along the frequencies.

Sometimes you receive two repeaters at the same time, one more faintly than the other, giving a bit of an echo chamber effect.
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GalaxyFlyer
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Re: Air Traffic Control Frequencies

Fri Nov 09, 2018 2:41 pm

Same thing across northern Canada with Edmonton.

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seb146
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Re: Air Traffic Control Frequencies

Fri Nov 09, 2018 10:44 pm

Starlionblue wrote:
fr8mech wrote:
Well, well, you learn something new everyday.

So, are the repeaters used to increase the range over the "theoretically optimal" 200NM range, or just to provide coverage where line-of-sight may be impeded by terrain?


I think mostly to increase range. Two places I can think of with repeaters are The Philippines and Australia. In Australia you might be talking to Brisbane Center and they'll periodically ask you "change to my frequency xxx.xx". Same station, different frequency in another area, and often the same on shift guy for a long while as you are passed along the frequencies.

Sometimes you receive two repeaters at the same time, one more faintly than the other, giving a bit of an echo chamber effect.


That was something I also was wondering. When I did ham radio work on 2 meters, I was able to talk into the Mission Ridge repeater from the top of the mountain ridge close to my home town. That was about 150NM. From there, Mission Ridge could be linked to Seattle and Spokane, neither of which I could hear. At the same spot, I could hear FM broadcast station KIOK and their repeater in town and they were a second or two off.
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Starlionblue
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Re: Air Traffic Control Frequencies

Sat Nov 10, 2018 1:50 am

seb146 wrote:
Starlionblue wrote:
fr8mech wrote:
Well, well, you learn something new everyday.

So, are the repeaters used to increase the range over the "theoretically optimal" 200NM range, or just to provide coverage where line-of-sight may be impeded by terrain?


I think mostly to increase range. Two places I can think of with repeaters are The Philippines and Australia. In Australia you might be talking to Brisbane Center and they'll periodically ask you "change to my frequency xxx.xx". Same station, different frequency in another area, and often the same on shift guy for a long while as you are passed along the frequencies.

Sometimes you receive two repeaters at the same time, one more faintly than the other, giving a bit of an echo chamber effect.


That was something I also was wondering. When I did ham radio work on 2 meters, I was able to talk into the Mission Ridge repeater from the top of the mountain ridge close to my home town. That was about 150NM. From there, Mission Ridge could be linked to Seattle and Spokane, neither of which I could hear. At the same spot, I could hear FM broadcast station KIOK and their repeater in town and they were a second or two off.


Yep. That's the way.

Once over the Philippines one of the repeaters went down, but no one noticed for a bit. Then a new plane came on frequency and couldn't reach Manila. So I offered to relay. But now I couldn't get them either! After a few minutes of everyone trying, we noticed we could hear each other but no one could hear Manila. Good times. No huge deal at that time as there was not much weather so we didn't have half a dozen aircraft deviating off the airways.

Manila came back on after a few minutes and sorted us out.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

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