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FAA Air Traffic Hearing Radio Stations

C

ChiefEngineer

Okay, Like I need this hassle. I have 6 kids and a loving wife. I have enough on my plate. Last Friday my day was FAA Hell.

I like the FAA, don't get me wrong. It appears airplanes in the SouthWest part of the State were hearing our State wide network feed at 20 some thousand feet. Normally we only broadcast below 10 thousand feet....


The air traffic control center at Indianapolis called the first number they heard, one of our mission programs. They called me, I called the FAA.

Luckily the airplanes were able to hear the towers at Evansville and Indianapolis over our broadcasts. Kind of like airplane musak. The places they heard this were between Terre Haute and Huntingburg, Indiana. The interference was heard on not just one but on all airplanes while in this area during the day Friday starting at around 9am. It went away at 2pm. Planes did not have any reports of the interference outside of this area. I would have expected the same interference on the hevier more congested path between Indy and Dayton for example.

As nothing changed and it went away I have a suspicion it was someone transmitting our internet signal. I didn't think to catch the IP address of people listening at this time. With the busiest air traffic week of the year upon us this could potentially be a mess. (IE - Die Hard, etc) The last thing I want is someone messing with airplanes.

There has been no explanation how an FM signal can be combined to broadcast AM in the air traffic band, and the tech staff at the FAA is working on it. With band pass filters on all our equipment I can't even start to think how this could happen. I know that 80 db down is still some power and line of sight is a possible factor.
 
We should get specific here... Like... was it Indy Intl, INDY CENTER, HUF (Hulman Fld - TH) or another airport authority?
And what frequency was this heard? If you can ascertain who it was, or what freq, thats the place to start IMO.
ATC uses specific frequencies in geographic locations.

Next question is, what feed are they hearing? And what are ALL the sources for the audio that was heard?
 
IndyKennyLee said:
We should get specific here... Like... was it Indy Intl, INDY CENTER, HUF (Hulman Fld - TH) or another airport authority?
And what frequency was this heard? If you can ascertain who it was, or what freq, thats the place to start IMO.
ATC uses specific frequencies in geographic locations.

Next question is, what feed are they hearing? And what are ALL the sources for the audio that was heard?
Click to expand...

And don't forget navaid frequencies. I have heard of audio getting into a VORTAC frequency used to talk to an ATC center on.
 
I heard a pilot transmission about 5:30 this afternoon reporting music on a freq. of 127.5. I was not paying much attention but caught part of what he was saying because I was in a building with with the aircraft radio in the background. There are a ton of freqs. for aircraft both civilian and military. They would make your head swim. I was south of Indianapolis and on the ground so I only heard the air half of the transmission and didn't catch who he was talking to on the ground. This may not be much help but at least you have one freq.
 
127.025 is the frequency. This is the airplane listen frequency for planes to hear air traffic controllers from the tower. This is the main channel that the tower communicates with the airplanes. Main contact has been Indy Center. This was the original contact.

Evansville has a transmitter at the airport and another transmitter at Huntingburg. The pilots use this frequency not only with Evansville,Terre Haute, Louisville, but also Indy. This is all air traffic according to the FAA tech folks. Every plane at 35,000 feet they said today is hearing this in a wide swath. At the Huntingburg and Evansville site they report no noise on the ground. The slope path from 35k feet would allow line of sight to most of the state.

So today I get a call from another tech. I also hear from Greg who is based at Evansville. The interference this day is not Christian music, as last week, but oldies. Turn Turn Turn from the Birds at 9:30 this morning.

Last week the tower could key their transmitter and override the interference. Today the interference could be covered by the tower but had hetrodyne and noise with the tower signal to the plane. I don't really want to say how they handled it today.

Any airplane hears this in a wide line from Huntingburg to Terre Haute, and either side. Since we have no transmitters above 2700 watts this was odd last week. We have several transmitters but most are translators 250 w or less. We have transmitters closer to Evansville but they don't share the programming which has been reported. Our only station S of 465 is at Edinburgh and it is a whopping 20 watts ERP.

Seemingly the interference clears when the overcast turns to sun. This was true Friday and today. Last Fri the interference started 8-9am and ended at 2pm. Today the interference started at the same time and then ended by 11am.

With Christian music being the source last week and pilots copying the phone number... and verification shows this announcement ran on our stations at the time it was heard. This was on station A with multiple translators and internet feed.

Today the feed heard by the planes was oldies. No clear indication the feed was our other set of stations. This is station B with multiple translators and internet feed.

Some of the translators share common sites. I have run several scenarios but can't find a way this can add up. Most of our sites have newer equipment, all solid state except for one tube amp. No common UHF feeds.

A few years ago someone with a tech truck monitored many stations in the state including ours after much less interference was reported and very non specific. This interference has been very clear, enough to identify artists, phone numbers, etc.

I didn't get a call this afternoon but Indy Center has me on speed dial so I am surprised there was no call this afternoon. Different frequency so possibly a different airport? Would like to know where it was? They may not all be talking to each other.

This is the busiest week of the year in the airport world. If you have the capability to listen to 127.025 plug it into your scanner. I have been to several of our sites just to check today. The pilots are listening to AM. Ofcourse all our feeds are FM.
 
ChiefEngineer said:
127.025 is the frequency. This is the airplane listen frequency for planes to hear air traffic controllers from the tower. This is the main channel that the tower communicates with the airplanes. Main contact has been Indy Center. This was the original contact.
Click to expand...

Sounds like you have a mess on your hands. You could have a couple of frequencies mixing together to create a harmonic on that frequency. Time to start turning off transmitters to try and locate one of the offenders. This is not a problem I wish on my worst enemy.
 
I have tried listening on the frequency when the air traffic controllers call but so far they haven't coordianted with planes so I can kill audio, transmitters, etc.
 
I'm 50' from the Oldies translator and the Icom IC-R1500 reveals that nothing is coming from here on 127.075.
 
I checked greensburg and Carthage and Wilkinson. I haven't been to Muncie.
 
It would be interesting to note the common (or at least - the same general locations) of Station "A" and Station "B". Maybe there is nothing wrong with YOUR equipment. If aeroplanes can hear audio "plane" as day, then I would guess that no amount of intermod would cause "perfectly clear audio". Those AM transcievers can only be 5 or 10 Khz wide. I would tend to believe that if they were hearing a "mix", it would be very raspy sounding. My bet is on someone causing this with something that was intended for aircraft transmission. You gotta keep that in mind as well. Track down where someone could possibly hear "A" and "B" together, and then place the one colocation in the bunch, where ATC has complained...

You could also sample all your sites with a spec an to verify that you are clean.
 
Several years ago, the FAA called 104.5 and ordered an immediate shut down due to interference. High altitude flights mainly west of Indy were hearing Gold 104.5 instead of Indianapolis Center.
We asked for permission to switch to the Hawthorne Ave. Aux site, they granted that and the problem was gone. We went through the main plant at Butler with a spectrum analyzer we borrowed from WISH TV and found the site was clean. Three days later, we asked for permission to resume at the main site, while the FAA monitored and contacted aircraft in the affected area to see if we were still giving the planes the best oldies. There was no problem and Dr. what's his name with Great Lakes, gave us permission to stay on as authorized. They caulked it up to atmospherics.
By the way, when they say shut down now -- they are serious.
 
IndyKennyLee said:
Those AM transcievers can only be 5 or 10 Khz wide. I would tend to believe that if they were hearing a "mix", it would be very raspy sounding. My bet is on someone causing this with something that was intended for aircraft transmission.
Click to expand...

Just for the record...we use separate transmitters and receivers. The only transceivers in use are for portable, emergency communications. Most of our receivers have a 25kHz bandwidth. Some are 50kHz.
 
The aircraft radios are not transceivers? I understand the ground units are receivers located at point x or y with a control tower transmitter.

We have had scanners locked on the aircraft frequency and haven't heard from anyone. Hopefully this means the problems have ended.
 
I was assuming the radios on the ground; and those are as you describe. (At x and Y locations; most tower transmitters are located in the immediate vicinity of the airport but not always at the tower) As far as the radios in the aircraft; I think it's safe to say they are transceivers and I know nothing about them.
 
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