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rjsampson
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Cell phone cuts out when aircraft takeoff overhead?

Tue Sep 24, 2019 8:16 am

Asking for a friend and her neighbor:

They live in an apartment right off of the departure end of a GA airport in San Diego (MYF). They claim their cell phone conversations are interrupted when aircraft takeoff overhead (I was the caller when this happened). I was pretty skeptical, and I suggested that it's probably spotty cell service (which they erroneously correlate to departing aircraft).

I visited them the next day to see for myself... it does seem like there's a correlation between one caller and the other, briefly going silent when an aircraft is overhead. For good measure, a neighbor with a different carrier showed a similar phenomenon. I was quite shocked, but I'm still skeptical.

Depending on the placement of cell phone towers relative to their apartment and the departure path of the aircraft: Is this sort of interference even theoretically possible?
"..your eyes will be forever turned skyward, for there.." yeah we know the DaVinci quote. But GA is so dang expensive these days! :(
 
flipdewaf
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Re: Cell phone cuts out when aircraft takeoff overhead?

Tue Sep 24, 2019 3:33 pm

It could be to do with the way the software handles the speaker and the microphone signals including feedback and noise suppression. It could be that the specific frequencies from the aircraft trigger unintended changes in the outputs.

Fred


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Siren
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Re: Cell phone cuts out when aircraft takeoff overhead?

Tue Sep 24, 2019 7:41 pm

Another thought from left field: this could be interference from the doppler radar mounted in the aircraft nose. They put out a huge amount of RF and consumer grade devices are not usually well shielded for that sort of thing...
 
Lemmy
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Re: Cell phone cuts out when aircraft takeoff overhead?

Tue Sep 24, 2019 9:47 pm

Probably caused by the radar altimeter. I know that, very close to an airport, planes flying overhead do disturb over-the-air TV signals. It's annoying.

Maybe someone who knows more about this stuff can comment on whether the wavelengths of radar and cell phones overlap enough to cause problems.

Edit:
departure end of a GA airport in San Diego (MYF).

Doubtful that GA aircraft would have any type of radar. So I'm not sure what's causing it. Did it the type of aircraft flying overhead seem to make a difference?
I am a patient boy ...
 
chimborazo
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Re: Cell phone cuts out when aircraft takeoff overhead?

Wed Sep 25, 2019 4:18 am

Maybe caused by the 100+ people with their phones on concentrated into a metal/carbon with impregnated conductivity strips tube sucking up all the bandwidth on the phone signal as their handsets are on max gain or whatever it’s called trying to keep/find the signal :-)

Actually I have no idea if that would have an effect because although phones are supposed to be off during takeoff and landing... from looking around on my flights and hearing the many pings and bings when coming in to land, it seems many folk cannot bear to be disconnected from the world for those additional few minutes of their flight, until they really are disconnected when the signal goes out of reach.
 
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zeke
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Re: Cell phone cuts out when aircraft takeoff overhead?

Wed Sep 25, 2019 5:23 am

Could the cell tower be fed by a microwave link that the aircraft flight path blocks ?
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
VSMUT
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Re: Cell phone cuts out when aircraft takeoff overhead?

Wed Sep 25, 2019 12:56 pm

Siren wrote:
Another thought from left field: this could be interference from the doppler radar mounted in the aircraft nose. They put out a huge amount of RF and consumer grade devices are not usually well shielded for that sort of thing...


Weather radars are generally supposed to be off on the ground. In my experience, they are only on when really needed (in bad weather, looking for embedded CBs), and would typically be turned off prior to landing.
 
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rjsampson
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Re: Cell phone cuts out when aircraft takeoff overhead?

Wed Sep 25, 2019 10:01 pm

flipdewaf wrote:
It could be that the specific frequencies from the aircraft trigger unintended changes in the outputs.

Fred


I was thinking along those lines, too. There is a localizer antenna very near their apartment, and I wonder if aircraft tuned into the ILS frequency might have something to do with it?
"..your eyes will be forever turned skyward, for there.." yeah we know the DaVinci quote. But GA is so dang expensive these days! :(
 
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Starlionblue
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Re: Cell phone cuts out when aircraft takeoff overhead?

Wed Sep 25, 2019 10:45 pm

VSMUT wrote:
Siren wrote:
Another thought from left field: this could be interference from the doppler radar mounted in the aircraft nose. They put out a huge amount of RF and consumer grade devices are not usually well shielded for that sort of thing...


Weather radars are generally supposed to be off on the ground. In my experience, they are only on when really needed (in bad weather, looking for embedded CBs), and would typically be turned off prior to landing.


What aircraft is this?

Our WX radars are on from taxi out to taxi in.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
BravoOne
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Re: Cell phone cuts out when aircraft takeoff overhead?

Thu Sep 26, 2019 3:07 am

Siren wrote:
Another thought from left field: this could be interference from the doppler radar mounted in the aircraft nose. They put out a huge amount of RF and consumer grade devices are not usually well shielded for that sort of thing...



You got me with that one. What doppler radar are you speaking about?
 
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Siren
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Re: Cell phone cuts out when aircraft takeoff overhead?

Thu Sep 26, 2019 3:14 pm

BravoOne wrote:
Siren wrote:
Another thought from left field: this could be interference from the doppler radar mounted in the aircraft nose. They put out a huge amount of RF and consumer grade devices are not usually well shielded for that sort of thing...



You got me with that one. What doppler radar are you speaking about?


This one: https://en.wikipedia.org/wiki/Pulse-Dop ... -Radar.jpg (EDIT: apparently the forum software doesn't allow linking of images.... oh well)

See this link for more information: https://en.wikipedia.org/wiki/Pulse-Doppler_radar
 
Okie
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Re: Cell phone cuts out when aircraft takeoff overhead?

Thu Sep 26, 2019 3:40 pm

rjsampson wrote:
Asking for a friend and her neighbor:


It is the noise cancelling feature of the phone. It is responding to the noise of the aircraft

Mine does the same when I am around loud equipment.

If it is an iPhone
Go to General Settings
Find the accessibility tab
Swipe down to hearing section
You can toggle NOISE CANCELLATION on and off

I highly recommend leaving it on otherwise the phone will pick up all kinds of background noise instead of just what is being spoken into the microphone.

Okie
 
BravoOne
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Re: Cell phone cuts out when aircraft takeoff overhead?

Thu Sep 26, 2019 4:57 pm

Siren wrote:
BravoOne wrote:
Siren wrote:
Another thought from left field: this could be interference from the doppler radar mounted in the aircraft nose. They put out a huge amount of RF and consumer grade devices are not usually well shielded for that sort of thing...



You got me with that one. What doppler radar are you speaking about?


This one: https://en.wikipedia.org/wiki/Pulse-Dop ... -Radar.jpg (EDIT: apparently the forum software doesn't allow linking of images.... oh well)

See this link for more information: https://en.wikipedia.org/wiki/Pulse-Doppler_radar



Thanks!
 
N47
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Re: Cell phone cuts out when aircraft takeoff overhead?

Thu Sep 26, 2019 5:15 pm

zeke wrote:
Could the cell tower be fed by a microwave link that the aircraft flight path blocks ?


I'm kind of leaning towards this also. Maybe the aircraft causes momentary multipath-fading to the telecomm signal.

Either this, or the post about noise cancellation.

The reason is that filtering has gotten really good now days so that aircraft frequencies and telecomm frequencies are pretty well seperated. Also not a lot of airborne frequencies emit near telecom frequencies (telecomm frequencies are roughly between 700 MHz - 2100 MHz. The UHF systems on aircraft that have antennas on the belly are DME, TCAS, Radar Bacon, and ADS-B, everything else is either VHF or higher than 2.1 GHz (Wx i think maybe somewhere between 8 - 12GHz (i stand to be corrected on this) way above telecomm bands). These systems usually less than 300W (and that's on the high side) but like I said the filtering is pretty good (on both sides) that it shouldn't affect telecomm signal. RFI is highly unlikely in a case like this but certainly not impossible.
 
N47
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Re: Cell phone cuts out when aircraft takeoff overhead?

Thu Sep 26, 2019 5:22 pm

rjsampson wrote:
flipdewaf wrote:
It could be that the specific frequencies from the aircraft trigger unintended changes in the outputs.

Fred


I was thinking along those lines, too. There is a localizer antenna very near their apartment, and I wonder if aircraft tuned into the ILS frequency might have something to do with it?


While that's a good thought, the LOC antennas are VHF from about 108 - 112 MHz they emit around 100 W and the radiation is very directional towards the runway. The aircraft only receives an ILS and does not emit anything else, with that said, if there is a DME associated with the ILS than the aircraft interrogates the DME by emitting ~1GHz pulses of around 100 - 200W. In this case the DME would be most probable to cause any issue.

This is certainly an interesting case, and thanks for sharing!
 
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rjsampson
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Re: Cell phone cuts out when aircraft takeoff overhead?

Thu Sep 26, 2019 10:22 pm

N47 wrote:
While that's a good thought, the LOC antennas are VHF from about 108 - 112 MHz they emit around 100 W and the radiation is very directional towards the runway. The aircraft only receives an ILS and does not emit anything else.


Yes of course... I should have known better (NAV antennae don't emit anything, only receive the constantly projecting, directional LOC signal)

N47 wrote:
with that said, if there is a DME associated with the ILS than the aircraft interrogates the DME by emitting ~1GHz pulses of around 100 - 200W. In this case the DME would be most probable to cause any issue.


That does make more sense, as this is an ILS/DME approach. Quick question: When does the aircraft interrogate the DME antenna? Are they constant pulses pushed out at certain time intervals? Does these pulses happen constantly while tuned into the ILS frequency at all times (even outside of range)? Or is there some sort of internal logic within the system that only makes those interrogations once the ILS/DME is captured by the instruments?
"..your eyes will be forever turned skyward, for there.." yeah we know the DaVinci quote. But GA is so dang expensive these days! :(
 
Woodreau
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Re: Cell phone cuts out when aircraft takeoff overhead?

Fri Sep 27, 2019 3:33 am

I'm leaning toward the noise cancellation software / circuitry on the phones -

Most piston general aviation don't have weather radar or Doppler radar.
Bonus animus sit, ab experientia. Quod salvatum fuerit de malis usu venit judicium.
 
N47
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Re: Cell phone cuts out when aircraft takeoff overhead?

Fri Sep 27, 2019 2:37 pm

rjsampson wrote:
N47 wrote:
While that's a good thought, the LOC antennas are VHF from about 108 - 112 MHz they emit around 100 W and the radiation is very directional towards the runway. The aircraft only receives an ILS and does not emit anything else.


Yes of course... I should have known better (NAV antennae don't emit anything, only receive the constantly projecting, directional LOC signal)

N47 wrote:
with that said, if there is a DME associated with the ILS than the aircraft interrogates the DME by emitting ~1GHz pulses of around 100 - 200W. In this case the DME would be most probable to cause any issue.


That does make more sense, as this is an ILS/DME approach. Quick question: When does the aircraft interrogate the DME antenna? Are they constant pulses pushed out at certain time intervals? Does these pulses happen constantly while tuned into the ILS frequency at all times (even outside of range)? Or is there some sort of internal logic within the system that only makes those interrogations once the ILS/DME is captured by the instruments?


DME pulses come in two Gaussian pairs 12-30 microseconds apart. On the approach phase, DME pulse pairs are spaced out randomly but are continuous. The most interrogations happen when the DME is first tuned until it locks on to the ground stations then the interrogation rate is reduced to something like 50 - 100 pulse pairs per second. DME's are usually paired with VOR or ILS so as soon as the NAV receiver is tuned the interrogations happen so in other words it does not wait until the ILS is captured.

I came across this page which details how you can get signal strength on mobile phone. You may be able to test the theory of RFI or multipath. If you see signal strength change on the mobile phone then it is most likely multipath but may by RFI. If it does not then its likely the noise cancellation circuitry of the phone.

Link: https://www.wilsonamplifiers.com/blog/best-smartphone-apps-to-find-your-mobile-signal-strength/
 
VSMUT
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Re: Cell phone cuts out when aircraft takeoff overhead?

Fri Sep 27, 2019 6:50 pm

Starlionblue wrote:
VSMUT wrote:
Siren wrote:
Another thought from left field: this could be interference from the doppler radar mounted in the aircraft nose. They put out a huge amount of RF and consumer grade devices are not usually well shielded for that sort of thing...


Weather radars are generally supposed to be off on the ground. In my experience, they are only on when really needed (in bad weather, looking for embedded CBs), and would typically be turned off prior to landing.


What aircraft is this?

Our WX radars are on from taxi out to taxi in.


On as in emitting, or just standby with the antenna stabilized?

Radar emissions are really harmful to people on the ground.
 
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Starlionblue
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Re: Cell phone cuts out when aircraft takeoff overhead?

Wed Oct 02, 2019 4:33 am

VSMUT wrote:
Starlionblue wrote:
VSMUT wrote:

Weather radars are generally supposed to be off on the ground. In my experience, they are only on when really needed (in bad weather, looking for embedded CBs), and would typically be turned off prior to landing.


What aircraft is this?

Our WX radars are on from taxi out to taxi in.


On as in emitting, or just standby with the antenna stabilized?

Radar emissions are really harmful to people on the ground.


Well, we can see weather on the departure path before we set takeoff thrust....
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
VSMUT
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Re: Cell phone cuts out when aircraft takeoff overhead?

Wed Oct 02, 2019 5:07 am

Starlionblue wrote:
VSMUT wrote:
Starlionblue wrote:

What aircraft is this?

Our WX radars are on from taxi out to taxi in.


On as in emitting, or just standby with the antenna stabilized?

Radar emissions are really harmful to people on the ground.


Well, we can see weather on the departure path before we set takeoff thrust....


You can do that just before ligning up, if necessary at all.
 
flipdewaf
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Re: Cell phone cuts out when aircraft takeoff overhead?

Mon Oct 07, 2019 5:32 am

rjsampson wrote:
flipdewaf wrote:
It could be that the specific frequencies from the aircraft trigger unintended changes in the outputs.

Fred


I was thinking along those lines, too. There is a localizer antenna very near their apartment, and I wonder if aircraft tuned into the ILS frequency might have something to do with it?

I was thinking only about sound waves and the feedback nothing to do with electromagnetic, I would think it lee likely that the specific parts of the electromagnetic spectrum are well protected but audio is a bit more difficult to do I think, maybe the call isn’t dropped for a few seconds but the speaker cuts out.

Fred


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