BAC Question

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N1SQB

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Ok, can someone explain to me why I am hearing Boston Air Center on 135.800 and most aircraft responses on 124.525? Some planes do respond right back on 135.8 but others come in on 124.525 clear as day, NOT an image. I have never encountered this.

Manny
 

ATCTech

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Are you in range to hear the ATC transmitter on 124.525? If not, then the same controller has both frequencies selected with aircraft on both and you're only able to hear the ground-based transmitter on one of them. In Canada we also have the ability to cross-couple frequencies so the aircraft on both (or more) frequencies also hear each other. The FAA may have adopted that technology as well.
 
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slayer816

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What you are hearing happens multiple times a day, all over the country.

The controller is covering more than one sector. The traffic usually doesn't warrant splitting sectors all day long. So only one controller will be handling multiple sectors. He/she does this by the above described method. You can usually figure out which is the "consolidated frequency" by which frequency you hear the aircraft on as well as the controller. The other frequency will just broadcast the controller.

This happens at the enroute level as well as the TRACON level. For example: Boston Tracon does not need 30 sectors open during the midnight shift. You will hear everyone on 133.00 (ID Departure) unless they changed it recently, but the controller will still broadcast on all sectors or a group of sectors.

What you are hearing is the same controller covering the Low sector (135.80) as well as the High sector (124.52). Now depending on the agreement with bordering facilities (NY TRACON for example), they may still hand off aircraft to the same frequency regardless of how ZBW is splitting sectors. It does not matter in this case since the same controller is talking and listening on both frequencies.

This also happens at the local level with the Tower controller working both the "Tower" frequency and the "Ground" frequency. Pilots will contact the ground frequency at all times and there will always be someone there in response. In our case it may be two different people, or one controller covering both.

Hope that helps.
 

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Another reason this scenario takes place from time to time is unscheduled maintenance or external problems with one of the frequencies. For example, if we have interference being reported on a particular frequency the sector may be assigned another frequency temporarily. The original frequency may not be technically taken out of service but is being intensely monitored by maintenance staff. Adjacent sectors, especially in other facilities, sometimes instinctively hand off traffic to the normal frequency for the sector rather than the alternate so the controller keeps both selected and moves traffic to the alternate on an as-needed basis. This might happen for an hour, part of a day or numerous days depending on the activity going on in the background.

Having been directly involved in a great many interference investigations where only airborne aircraft could hear (and hence report) the problem it was always a challenge to keep ATC using the frequency and collecting reports without the problem becoming too severe to continue using the frequency. We'd provide an alternate to the sector and let them decide if or when they needed to move everybody off of the problem frequency. We needed the aircraft to be our "ears" and in most cases they were more than happy to assist, workload on the flight deck permitting.
 

slayer816

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Exactly. Charlotte, NC was having that yesterday. Departing traffic kept hearing a TV or Radio station interfering with the frequencies they were using (ATC couldn't hear it, they relied on the pilots in this case). Also an area may have a dedicated frequency coverage. Our local traffic switches to different frequencies depending on where they may be located, all with the same controller (or not. They have the option).

There are many many scenarios. The most common is to balance traffic load as I mentioned in my first reply, but the reasoning may be one of a thousand. All involving controllers having the ability to talk/listen on multiple frequencies at once. Or just one.
 

N1SQB

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Back to normal!

Thanks for all your responses guys. I learned something new today. Funny thing to hear something different after 30 plus years of ATC traffic monitoring. All is back to normal now. I can hear different controllers and aircraft comms separately on the 124.525 and 135.800 frequencies.

Manny
 
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ATCTech

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You're most welcome Manny, glad we could help. As my tagline says, I've spent 34 years working right in the ATC environment, there's not much I haven't seen, or more correctly, responded to. As slayer816 says, there are a huge number of remote radio sites associated with ATC so just because you hear one frequency doesn't mean you'll hear another affiliated with the same ARTCC or TRACON. In the FAA world they're called RCAG sites, here in Canada we call them PALS, or "peripheral" sites. They're located to provide appropriate coverage for the area, be that "to the ground" or just for mid to high level flight. Frequency assignment coordination within the FAA and with us here north of the border is a complicated and never-ending project.

If you're interested in a little inside info, have a look at this thread:

http://forums.radioreference.com/aircraft-monitoring-forum/317886-moncton-centre-sectors-simulcasts-cross-coupling.html

I posted a couple of pictures with bit of a description of how the ATC voice switch control screen operate, including how frequencies can be cross-coupled to each other.

Bob
 
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JeffDS3

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A similar thing happened to me with my local. EMS dispatch. We have 3 countries using the same dispatch center, with each county on different frequencies. During certain hours when it's slow, they will consolidate a few areas to one dispatcher with them talking out via 2-3 frequencies, but unless your are monitoring the specific county they are talking to, you won't hear a response.
 

N1SQB

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ATCTech, here in CT. we have a repeater in Shelton, a town next to mine. This is the main reason why I can hear both sides of 134.00, 125.575, and only the controller on 128.100 which I am still trying to figure out where the aircraft comms are heard.

Manny
 

AirScan

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Funny thing to hear something different after 30 plus years of ATC traffic monitoring. All is back to normal now. I can hear different controllers and aircraft comms separately on the 124.525 and 135.800 frequencies.
That particular configuration, 135.800 combined with 124.525, has been used for years. Granted during the day shift it's not that common, seems to be used more during the weekends. What time did you hear this ?

There is even a very rarely used 3rd sector they can fit in vertically between 135.800 and 124.525, using 132.300, that from what I've been told it is only needed a few times per year. Although I have noticed they have used 132.300 as a backup frequency on occasion.

On the night shift 135.800/124.525 combine with the other Boston Center Area "C" frequencies to the north 124.85/133.42/126.225/(118.425) where they seem to use both 135.800 and 133.425 as the primaries.

AS
 

movinon

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I noticed that in Midwest City also. I had two scanners going trying to catch the Thunderbirds arriving for a air show some time back.
The tower was communicating with the military guys on one frequency but those transmissions were coming out also on a civilian frequency.
 

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only the controller on 128.100 which I am still trying to figure out where the aircraft comms are heard.
You will find the aircraft on 134.300

AS
 

N1SQB

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That particular configuration, 135.800 combined with 124.525, has been used for years. Granted during the day shift it's not that common, seems to be used more during the weekends. What time did you hear this ?

There is even a very rarely used 3rd sector they can fit in vertically between 135.800 and 124.525, using 132.300, that from what I've been told it is only needed a few times per year. Although I have noticed they have used 132.300 as a backup frequency on occasion.

On the night shift 135.800/124.525 combine with the other Boston Center Area "C" frequencies to the north 124.85/133.42/126.225/(118.425) where they seem to use both 135.800 and 133.425 as the primaries.

AS
Most of my ATC monitoring is in the morning time. I heard it this morning around 9:30 am EST. Sounds like I'm gonna have to listen in at night. LOL

Manny
 

N1SQB

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You will find the aircraft on 134.300

AS
Thanks, but guess what? As I read your post, I tuned in and well, BOTH sides are heard on 128,100, I hear nothing on 134.300. What the heck is going on here...I was NOT hearing the aircraft on this frequency for a while. Now I can hear everything on it. I know I'm not going bonkers...or am I ?????:roll:

Manny
 
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AirScan

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I know I'm not going bonkers...or am I ?????
When traffic is busy the Sectors are split/separate. You will find however a lot of the time the Sectors are combined in which case you will hear the controller on 128.100 and the aircraft on 134.300 as this is usually used as the primary frequency.

Listening now (the sector is covered over at LiveATC) it sounds like the sectors are combined and they are using both 134.300 and 128.100 for aircraft. I suspect they might be in the middle of re-configuring the sectors as for years 134.300 has been used as the primary. Check again a bit later and I bet you will hear all aircraft on 134.300.

AS
 

AirScan

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As I was typing that it seems like they have switched back to all aircraft now on 134.300 (sectors combined). Is this what your are hearing now too ?
 

AirScan

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Yeah they only split off 128.100 as a stand alone sector (aircraft on 128.10) during the busy peak times, I'm guessing around 25% of the time during the day shift.

On the night shift 134.30/(128.100) also takes over for 125.575 (aircraft on 134.300).

AS
 
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ATCTech

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ATCTech, here in CT. we have a repeater in Shelton, a town next to mine. This is the main reason why I can hear both sides of 134.00, 125.575, and only the controller on 128.100 which I am still trying to figure out where the aircraft comms are heard.

Manny
Cool. Just to be perfectly clear, none of these sites are repeaters in the sense we think them for police radios and so forth. They're all discrete frequencies and it's the voice switch equipment used by ATC that allows them to cross-couple frequencies together. You won't see the same frequency used by the same ATC facility (for en route traffic) at multiple locations except in some very specialized situations. We do this in the northern part of Canada where we set up a "ring" of sites that all use the same frequency (for the same sector) and employ a voting receiver system to determine which site is used to transmit to and receive from any particular aircraft. The aircraft can all hear each other because of altitude, but the geographic area needing coverage means that ground based equipment cannot provide coverage from a single site. And we're talking the geographic area equivalent to several U.S. states combined, not a small pocket of territory. (Around Hudson Bay to be specific.)

If you hear the same aircraft on two or more frequencies simultaneously then for sure ATC is cross-coupling frequencies to absorb more airspace into the same sector during quieter hours. Any particular aircraft is only on one of the frequencies but it's being rebroadcast on the others so all the traffic hears everybody else.

BTW Manny, you should be able to find the physical location for each of the frequencies you monitor here (or elsewhere online) which should give you a rough idea of what area the sector is covering at any particular part of the day.

Here's a chart for Toronto ACC which gives each frequency, it's purpose and the location of the radio equipment. With Google Maps or similar at hand it's pretty easy to visualize the approximate coverage for each frequency. Hopefully you can find the same for your area.

http://www.radioreference.com/apps/db/?aid=3965

Bob
 
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N1SQB

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Cool. Just to be perfectly clear, none of these sites are repeaters in the sense we think them for police radios and so forth. They're all discrete frequencies and it's the voice switch equipment used by ATC that allows them to cross-couple frequencies together. You won't see the same frequency used by the same ATC facility (for en route traffic) at multiple locations except in some very specialized situations. We do this in the northern part of Canada where we set up a "ring" of sites that all use the same frequency (for the same sector) and employ a voting receiver system to determine which site is used to transmit to and receive from any particular aircraft. The aircraft can all hear each other because of altitude, but the geographic area needing coverage means that ground based equipment cannot provide coverage from a single site. And we're talking the geographic area equivalent to several U.S. states combined, not a small pocket of territory. (Around Hudson Bay to be specific.)

If you hear the same aircraft on two or more frequencies simultaneously then for sure ATC is cross-coupling frequencies to absorb more airspace into the same sector during quieter hours. Any particular aircraft is only on one of the frequencies but it's being rebroadcast on the others so all the traffic hears everybody else.

BTW Manny, you should be able to find the physical location for each of the frequencies you monitor here (or elsewhere online) which should give you a rough idea of what area the sector is covering at any particular part of the day.

Here's a chart for Toronto ACC which gives each frequency, it's purpose and the location of the radio equipment. With Google Maps or similar at hand it's pretty easy to visualize the approximate coverage for each frequency. Hopefully you can find the same for your area.

Toronto (CZYZ) Scanner Frequencies and Radio Frequency Reference

Bob
Bob;

Thank you and Airscan for all the information you shared today. It's nice to gain a little more insight into the world of ATC. It certainly cleared up a lot of things for me. ATC was going to be my career of choice right after high school. Unfortunately diabetes got in my way.
It couldn't stop me from listening in though! Lol

BTW, is this what you told me to look for?
http://www.radioreference.com/apps/db/?rpt=6&aid=2248


Manny
 
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