Radio interference? in Class B airspace

[Vasu Murthy]

So I was on my first SF Bay Tour, with flight following, cleared into SFO Class B and was flying abeam SFO, enjoying the views. As I passed the airport northbound, noise started building in my headphones, and by the time I was flying over Brisbane, the noise had built up so much that I could no longer hear the tower. I called out radio check a couple times, but could not hear the response. I headed straight out of Class B, and the noise continued as I crossed over Golden Gate bridge. I changed frequency to norcal approach, and this time there was no noise. I asked for flight following, and they gave me a new code, and I proceeded on.

Checking LiveATC later on, SFO Tower asked me to head out of Class B after my first radio check call, and tried to raise me a couple of times, and gave up. Two questions:

1) Have you encountered noise like this? What could be the cause? - My passenger also heard it, and only on the tower frequency, north of SFO
2) Should I have told Norcal about my previous squawk code so they'll close the FF?

 

[luvflyin]

So I was on my first SF Bay Tour, with flight following, cleared into SFO Class B and was flying abeam SFO, enjoying the views. As I passed the airport northbound, noise started building in my headphones, and by the time I was flying over brisbane, the noise had built up so much that I could no longer hear the tower. I called out radio check a couple times, but could not hear the response. I headed straight out of Class B, and the noise continued as I crossed over Golden Gate bridge. I changed frequency to norcal approach, and this time there was no noise. I asked for flight following, and they gave me a new code, and I proceeded on.

Checking LiveATC later on, SFO Tower asked me to head out of Class B after my first radio check call, and tried to raise me a couple of times, and gave up. Two questions:

1) Have you encountered noise like this? What could be the cause? - My passenger also heard it, and only on the tower frequency, north of the SFO
2) Should I have told Norcal about my previous squawk code so they'll close the FF?

2) It's not actually a 'closing' of FF. It's always a good idea in a situation like this to let the controller know whats going on. No particular phraseology, just say what happenned. Something like 'I was with the Tower but lost com with them.'

 

[GaryV]

My radios tend to get swamped as I pass the Cedar Hill broadcast towers in the Dallas area. The interference is only bad for a minute or two and so far I can here the tower at KGPM, it’s just noisy.
Gary

 

[Vasu Murthy]

2) It's not actually a 'closing' of FF. It's always a good idea in a situation like this to let the controller know whats going on. No particular phraseology, just say what happenned. Something like 'I was with the Tower but lost com with them.'

Thanks. Generally, what would the tower or center do if they lose comms with an aircraft? Assuming they still had radar contact until I changed squawk. Would the new squawk be available to them?

 

[Vasu Murthy]

My radios tend to get swamped as I pass the Cedar Hill broadcast towers in the Dallas area. The interference is only bad for a minute or two and so far I can here the tower at KGPM, it’s just noisy.
Gary

Thanks. I am beginning to think the issue was with my radios. LiveATC does not have the noise and no one else seem to have reported it, though I was likelt only one at 2000 ft. Is there anything that can cause a radio to generate noise only at certain frequencies?

 

[luvflyin]

Thanks. Generally, what would the tower or center do if they lose comms with an aircraft? Assuming they still had radar contact until I changed squawk. Would the new squawk be available to them?

Yes. If you had told Approach you had been with Tower and lost Com they would probably not have given you a new code. They'd just have called the Tower and said 'we got this guy now.' Tower then could have transferred control of your 'Track' to Approach. There could have been some combination of events that would have resulted in Approach giving you a new code though. Anyway, it's never a good idea to have been working with one Controller and then just 'pop up' with another Controller without explanation if your 'business' with the previous Controller isn't complete.

 

[denverpilot]

Thanks. I am beginning to think the issue was with my radios. LiveATC does not have the noise and no one else seem to have reported it, though I was likelt only one at 2000 ft. Is there anything that can cause a radio to generate noise only at certain frequencies?

Without getting into it deeply, yes. IF mixes and 2B+A or 2A+B but most aviation radios use the same IF as all the others, so quite unlikely.

Usually it’s just crap from the ground transmitters (intentional or unintentional transmitters) in the area and any airplane flying in the same general location will hear it.

If it sticks to a particular airplane, it’s usually on on-board noisemaker.

Try turning everything all the way off (including chargers and any non-certified gadgetry you’ve brought on board in your flight bag, iPad, portable GPS, etc.) other than the single radio and see if it continues.

Some folks have even had problems with antenna placement and parasitic noise from the diodes / transistors in the output stages of ELTs at certain frequencies when the ELT antenna was too close to other antennas and made for a nice intermodulation interference maker.

My King radios in my airplane don’t like something near @jesse ‘s home airport on one of their approach frequencies. Rhythmic opening and closing of the squelch on 123.0, I think it was. Don’t remember. But asking them to use their alternate frequency was always granted and worked fine. All depended on how long I wanted to listen to it.

Can be all sorts of things. An RF engineer friend says, “Passive Intermodulation interference is the devil’s snack food.” He works for FCC these days, hunting interference crap down, amongst other duties which are far more interesting.

 

[Vasu Murthy]

Without getting into it deeply, yes. IF mixes and 2B+A or 2A+B but most aviation radios use the same IF as all the others, so quite unlikely.

Usually it’s just crap from the ground transmitters (intentional or unintentional transmitters) in the area and any airplane flying in the same general location will hear it.

If it sticks to a particular airplane, it’s usually on on-board noisemaker.

Try turning everything all the way off (including chargers and any non-certified gadgetry you’ve brought on board in your flight bag, iPad, portable GPS, etc.) other than the single radio and see if it continues.

Some folks have even had problems with antenna placement and parasitic noise from the diodes / transistors in the output stages of ELTs at certain frequencies when the ELT antenna was too close to other antennas and made for a nice intermodulation interference maker.

My King radios in my airplane don’t like something near @jesse ‘s home airport on one of their approach frequencies. Rhythmic opening and closing of the squelch on 123.0, I think it was. Don’t remember. But asking them to use their alternate frequency was always granted and worked fine. All depended on how long I wanted to listen to it.

Can be all sorts of things. An RF engineer friend says, “Passive Intermodulation interference is the devil’s snack food.” He works for FCC these days, hunting interference crap down, amongst other duties which are far more interesting.

Appreciate it. I'll try turning off electronics next time.

 

[Vasu Murthy]

Appreciate it. I'll try turning off electronics next time.

Interestingly, found an old report of a very similar incident from 1990:

http://www.37000feet.com/report/141...A-experiences-loss-of-communication-frequency

 

[arnoha]

I've flown that path many times. I've not encountered any interference that I couldn't source to the plane. I have in other spots in the Bay Area, though it's often pirate radio, and that's easy to identify (it isn't static).

Most often, I find that I've introduced a noisy USB car charger to the plane. If I drape the Stratus charging cable near the radios, that's often an issue. iPads and Stratus seem to be bigger offenders than phones. I think it's due to the much higher power draw. Not saying that that was your issue, just something to check.

 

[Vasu Murthy]

I've flown that path many times. I've not encountered any interference that I couldn't source to the plane. I have in other spots in the Bay Area, though it's often pirate radio, and that's easy to identify (it isn't static).

Most often, I find that I've introduced a noisy USB car charger to the plane. If I drape the Stratus charging cable near the radios, that's often an issue. iPads and Stratus seem to be bigger offenders than phones. I think it's due to the much higher power draw. Not saying that that was your issue, just something to check.

Thanks. I had two USB chargers in the plane apart from my iPhone, will try turning them off if that happens next time. Really puzzling that the static was still loud on 120.5 over Golden Gate bridge, other frequencies (135.1, 127.8) were clear.

 

[arnoha]

Thanks. I had two USB chargers in the plane apart from my iPhone, will try turning them off if that happens next time. Really puzzling that the static was still loud on 120.5 over Golden Gate bridge, other frequencies (135.1, 127.8) were clear.

Not that surprising. There may be one specific resonating overtone that the radio is picking up and it's a multiple of 120.5. The fact that it was still loud after traveling some distance really suggests the source is in the plane itself, not the ground. Another thing...120.5...that's really close to 121.5, a frequency your ELT uses. Might also be the ELT. There was a thread on that recently here.

 

[Vasu Murthy]

Not that surprising. There may be one specific resonating overtone that the radio is picking up and it's a multiple of 120.5. The fact that it was still loud after traveling some distance really suggests the source is in the plane itself, not the ground. Another thing...120.5...that's really close to 121.5, a frequency your ELT uses. Might also be the ELT. There was a thread on that recently here.

Thanks, hadn't thought of that!

 

[Paulie]

My radios tend to get swamped as I pass the Cedar Hill broadcast towers in the Dallas area. The interference is only bad for a minute or two and so far I can here the tower at KGPM, it’s just noisy.
Gary

Been there, the tower told me to expect to lose them while over the towers.

 

[slacktide]

First of all it's very important that you turn on your ADF radio. Set it to 1010 on your dial, and let the radio frequency energy from K-101 overload your little tuner until it distorts very highly. And right at the point of that extreme distortion, there's the big chairs. I'm not exactly sure, but I think that's where all the sewer water from Oakland goes.

And then, by then, you'll be out of all that distortion, and you'll be looking East, toward the hills, and if it's at night, you'll see the little red lights flashing on my favorite ham radio repeater station -- that's WR6 Automatic Bowel Movement.

And any of you who are into jamming, keep talking, keep jamming, because I'll be listening on my scanner radio, and just maybe...you'll be on the next album.

 

[danhagan]

Have you encountered noise like this? What could be the cause? - My passenger also heard it, and only on the tower frequency, north of SFO

I had it BAD in my Tiger in the SAME spot near the mountain in Class C. Tried everything - here were the avionic's shops maneuvers:

1. Make sure ELT wasn't the cause by disconnecting for one test flight
2. They thought it might be ground interference (it wasn't)
3. Got progressively worse and was happening more often in different locations. Ended up changing coaxial and both antennas (that didn't work)

Turned out it was the squelch break on the KX-155. Volume knob gets loose "side to side" not in and out. Sent radio in for repair ($150) and that solved it. Never used that avionics shops again (there were additional issues besides radio).

 

[Vasu Murthy]

I had it BAD in my Tiger in the SAME spot near the mountain in Class C. Tried everything - here were the avionic's shops maneuvers:

1. Make sure ELT wasn't the cause by disconnecting for one test flight
2. They thought it might be ground interference (it wasn't)
3. Got progressively worse and was happening more often in different locations. Ended up changing coaxial and both antennas (that didn't work)

Turned out it was the squelch break on the KX-155. Volume knob gets loose "side to side" not in and out. Sent radio in for repair ($150) and that solved it. Never used that avionics shops again (there were additional issues besides radio).

Thank you! WIll certainly take a look at it. This Citabria does not have KX-155, but may have similar issues.

 

[Stan Cooper]

I've had VHF aviation band interference apparently caused by leaving my cellphone on when flying over certain geographic areas, and suspect intermod interference from multiple VHF and UHF repeaters on mountain tops (like Grizzly Peak in the Berkeley Hills). When I turn off my cellphone or put it in "airplane mode" the interference ceases.

 

[midwestpa24]

We recently had interference over our CTAF frequency. It would cut in and out with classic rock. We discussed with our FAA tech ops folks, and they figured a radio station somewhere had a "dirty" transmitter. They were to pass it along to their interference people at the FCC. A day or two later it disappeared.

 

[Lindberg]

My radios tend to get swamped as I pass the Cedar Hill broadcast towers in the Dallas area. The interference is only bad for a minute or two and so far I can here the tower at KGPM, it’s just noisy.
Gary

I get it in that area as well. Have been told I need better shielding on the radio.

 

[Bubba236]

Thank you! WIll certainly take a look at it. This Citabria does not have KX-155, but may have similar issues.

I know this post is old, but I have the exact same problem in Class B near KSFO. 120.9 and 120.5. Did you ever figure it out?
Both my radios one on the IFD540 avidyne and the 2nd radio is Dynon. really bad interference to the point with no Audio can be heard. seems like not squelching radios from Sutro Tower. I have brand new panel with new co-ax's and new antennas. Just had the antennas and cable tested by avionics shop and found no trouble. I tried second time in the area with everything turned off or disconnected. (still had audio panel, PFD and ELT) and it was exactly the same.

 

[Doug Reid]

Are you flying close to radio broadcast towers ?

 

[Bubba236]

Are you flying close to radio broadcast towers ?

Yes, that is the only way to do the san francisco bay tour. However, I've been doing this in other airplanes for decades and never have a problem